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23 results

deparse.c

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    • Tom Lane's avatar
      5b68d816
      Fix contrib/postgres_fdw's remote-estimate representation of array Params. · 5b68d816
      Tom Lane authored
      We were emitting "(SELECT null::typename)", which is usually interpreted
      as a scalar subselect, but not so much in the context "x = ANY(...)".
      This led to remote-side parsing failures when remote_estimate is enabled.
      A quick and ugly fix is to stick in an extra cast step,
      "((SELECT null::typename)::typename)".  The cast will be thrown away as
      redundant by parse analysis, but not before it's done its job of making
      sure the grammar sees the ANY argument as an a_expr rather than a
      select_with_parens.  Per an example from Hannu Krosing.
      5b68d816
      History
      Fix contrib/postgres_fdw's remote-estimate representation of array Params.
      Tom Lane authored
      We were emitting "(SELECT null::typename)", which is usually interpreted
      as a scalar subselect, but not so much in the context "x = ANY(...)".
      This led to remote-side parsing failures when remote_estimate is enabled.
      A quick and ugly fix is to stick in an extra cast step,
      "((SELECT null::typename)::typename)".  The cast will be thrown away as
      redundant by parse analysis, but not before it's done its job of making
      sure the grammar sees the ANY argument as an a_expr rather than a
      select_with_parens.  Per an example from Hannu Krosing.
    deparse.c 48.07 KiB
    /*-------------------------------------------------------------------------
     *
     * deparse.c
     *		  Query deparser for postgres_fdw
     *
     * This file includes functions that examine query WHERE clauses to see
     * whether they're safe to send to the remote server for execution, as
     * well as functions to construct the query text to be sent.  The latter
     * functionality is annoyingly duplicative of ruleutils.c, but there are
     * enough special considerations that it seems best to keep this separate.
     * One saving grace is that we only need deparse logic for node types that
     * we consider safe to send.
     *
     * We assume that the remote session's search_path is exactly "pg_catalog",
     * and thus we need schema-qualify all and only names outside pg_catalog.
     *
     * We do not consider that it is ever safe to send COLLATE expressions to
     * the remote server: it might not have the same collation names we do.
     * (Later we might consider it safe to send COLLATE "C", but even that would
     * fail on old remote servers.)  An expression is considered safe to send only
     * if all collations used in it are traceable to Var(s) of the foreign table.
     * That implies that if the remote server gets a different answer than we do,
     * the foreign table's columns are not marked with collations that match the
     * remote table's columns, which we can consider to be user error.
     *
     * Portions Copyright (c) 2012-2014, PostgreSQL Global Development Group
     *
     * IDENTIFICATION
     *		  contrib/postgres_fdw/deparse.c
     *
     *-------------------------------------------------------------------------
     */
    #include "postgres.h"
    
    #include "postgres_fdw.h"
    
    #include "access/heapam.h"
    #include "access/htup_details.h"
    #include "access/sysattr.h"
    #include "access/transam.h"
    #include "catalog/pg_collation.h"
    #include "catalog/pg_namespace.h"
    #include "catalog/pg_operator.h"
    #include "catalog/pg_proc.h"
    #include "catalog/pg_type.h"
    #include "commands/defrem.h"
    #include "nodes/nodeFuncs.h"
    #include "optimizer/clauses.h"
    #include "optimizer/var.h"
    #include "parser/parsetree.h"
    #include "utils/builtins.h"
    #include "utils/lsyscache.h"
    #include "utils/syscache.h"
    
    
    /*
     * Global context for foreign_expr_walker's search of an expression tree.
     */
    typedef struct foreign_glob_cxt
    {
    	PlannerInfo *root;			/* global planner state */
    	RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
    } foreign_glob_cxt;
    
    /*
     * Local (per-tree-level) context for foreign_expr_walker's search.
     * This is concerned with identifying collations used in the expression.
     */
    typedef enum
    {
    	FDW_COLLATE_NONE,			/* expression is of a noncollatable type */
    	FDW_COLLATE_SAFE,			/* collation derives from a foreign Var */
    	FDW_COLLATE_UNSAFE			/* collation derives from something else */
    } FDWCollateState;
    
    typedef struct foreign_loc_cxt
    {
    	Oid			collation;		/* OID of current collation, if any */
    	FDWCollateState state;		/* state of current collation choice */
    } foreign_loc_cxt;
    
    /*
     * Context for deparseExpr
     */
    typedef struct deparse_expr_cxt
    {
    	PlannerInfo *root;			/* global planner state */
    	RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
    	StringInfo	buf;			/* output buffer to append to */
    	List	  **params_list;	/* exprs that will become remote Params */
    } deparse_expr_cxt;
    
    /*
     * Functions to determine whether an expression can be evaluated safely on
     * remote server.
     */
    static bool foreign_expr_walker(Node *node,
    					foreign_glob_cxt *glob_cxt,
    					foreign_loc_cxt *outer_cxt);
    static bool is_builtin(Oid procid);
    
    /*
     * Functions to construct string representation of a node tree.
     */
    static void deparseTargetList(StringInfo buf,
    				  PlannerInfo *root,
    				  Index rtindex,
    				  Relation rel,
    				  Bitmapset *attrs_used,
    				  List **retrieved_attrs);
    static void deparseReturningList(StringInfo buf, PlannerInfo *root,
    					 Index rtindex, Relation rel,
    					 bool trig_after_row,
    					 List *returningList,
    					 List **retrieved_attrs);
    static void deparseColumnRef(StringInfo buf, int varno, int varattno,
    				 PlannerInfo *root);
    static void deparseRelation(StringInfo buf, Relation rel);
    static void deparseStringLiteral(StringInfo buf, const char *val);
    static void deparseExpr(Expr *expr, deparse_expr_cxt *context);
    static void deparseVar(Var *node, deparse_expr_cxt *context);
    static void deparseConst(Const *node, deparse_expr_cxt *context);
    static void deparseParam(Param *node, deparse_expr_cxt *context);
    static void deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context);
    static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
    static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
    static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
    static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
    static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
    						 deparse_expr_cxt *context);
    static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
    static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
    static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
    static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
    static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
    				 deparse_expr_cxt *context);
    static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
    					   deparse_expr_cxt *context);
    
    
    /*
     * Examine each qual clause in input_conds, and classify them into two groups,
     * which are returned as two lists:
     *	- remote_conds contains expressions that can be evaluated remotely
     *	- local_conds contains expressions that can't be evaluated remotely
     */
    void
    classifyConditions(PlannerInfo *root,
    				   RelOptInfo *baserel,
    				   List *input_conds,
    				   List **remote_conds,
    				   List **local_conds)
    {
    	ListCell   *lc;
    
    	*remote_conds = NIL;
    	*local_conds = NIL;
    
    	foreach(lc, input_conds)
    	{
    		RestrictInfo *ri = (RestrictInfo *) lfirst(lc);
    
    		if (is_foreign_expr(root, baserel, ri->clause))
    			*remote_conds = lappend(*remote_conds, ri);
    		else
    			*local_conds = lappend(*local_conds, ri);
    	}
    }
    
    /*
     * Returns true if given expr is safe to evaluate on the foreign server.
     */
    bool
    is_foreign_expr(PlannerInfo *root,
    				RelOptInfo *baserel,
    				Expr *expr)
    {
    	foreign_glob_cxt glob_cxt;
    	foreign_loc_cxt loc_cxt;
    
    	/*
    	 * Check that the expression consists of nodes that are safe to execute
    	 * remotely.
    	 */
    	glob_cxt.root = root;
    	glob_cxt.foreignrel = baserel;
    	loc_cxt.collation = InvalidOid;
    	loc_cxt.state = FDW_COLLATE_NONE;
    	if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt))
    		return false;
    
    	/* Expressions examined here should be boolean, ie noncollatable */
    	Assert(loc_cxt.collation == InvalidOid);
    	Assert(loc_cxt.state == FDW_COLLATE_NONE);
    
    	/*
    	 * An expression which includes any mutable functions can't be sent over
    	 * because its result is not stable.  For example, sending now() remote
    	 * side could cause confusion from clock offsets.  Future versions might
    	 * be able to make this choice with more granularity.  (We check this last
    	 * because it requires a lot of expensive catalog lookups.)
    	 */
    	if (contain_mutable_functions((Node *) expr))
    		return false;
    
    	/* OK to evaluate on the remote server */
    	return true;
    }
    
    /*
     * Check if expression is safe to execute remotely, and return true if so.
     *
     * In addition, *outer_cxt is updated with collation information.
     *
     * We must check that the expression contains only node types we can deparse,
     * that all types/functions/operators are safe to send (which we approximate
     * as being built-in), and that all collations used in the expression derive
     * from Vars of the foreign table.	Because of the latter, the logic is
     * pretty close to assign_collations_walker() in parse_collate.c, though we
     * can assume here that the given expression is valid.
     */
    static bool
    foreign_expr_walker(Node *node,
    					foreign_glob_cxt *glob_cxt,
    					foreign_loc_cxt *outer_cxt)
    {
    	bool		check_type = true;
    	foreign_loc_cxt inner_cxt;
    	Oid			collation;
    	FDWCollateState state;
    
    	/* Need do nothing for empty subexpressions */
    	if (node == NULL)
    		return true;
    
    	/* Set up inner_cxt for possible recursion to child nodes */
    	inner_cxt.collation = InvalidOid;
    	inner_cxt.state = FDW_COLLATE_NONE;
    
    	switch (nodeTag(node))
    	{
    		case T_Var:
    			{
    				Var		   *var = (Var *) node;
    
    				/*
    				 * If the Var is from the foreign table, we consider its
    				 * collation (if any) safe to use.	If it is from another
    				 * table, we treat its collation the same way as we would a
    				 * Param's collation, ie it's not safe for it to have a
    				 * non-default collation.
    				 */
    				if (var->varno == glob_cxt->foreignrel->relid &&
    					var->varlevelsup == 0)
    				{
    					/* Var belongs to foreign table */
    					collation = var->varcollid;
    					state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
    				}
    				else
    				{
    					/* Var belongs to some other table */
    					if (var->varcollid != InvalidOid &&
    						var->varcollid != DEFAULT_COLLATION_OID)
    						return false;
    
    					/* We can consider that it doesn't set collation */
    					collation = InvalidOid;
    					state = FDW_COLLATE_NONE;
    				}
    			}
    			break;
    		case T_Const:
    			{
    				Const	   *c = (Const *) node;
    
    				/*
    				 * If the constant has nondefault collation, either it's of a
    				 * non-builtin type, or it reflects folding of a CollateExpr;
    				 * either way, it's unsafe to send to the remote.
    				 */
    				if (c->constcollid != InvalidOid &&
    					c->constcollid != DEFAULT_COLLATION_OID)
    					return false;
    
    				/* Otherwise, we can consider that it doesn't set collation */
    				collation = InvalidOid;
    				state = FDW_COLLATE_NONE;
    			}
    			break;
    		case T_Param:
    			{
    				Param	   *p = (Param *) node;
    
    				/*
    				 * Collation handling is same as for Consts.
    				 */
    				if (p->paramcollid != InvalidOid &&
    					p->paramcollid != DEFAULT_COLLATION_OID)
    					return false;
    
    				collation = InvalidOid;
    				state = FDW_COLLATE_NONE;
    			}
    			break;
    		case T_ArrayRef:
    			{
    				ArrayRef   *ar = (ArrayRef *) node;;
    
    				/* Assignment should not be in restrictions. */
    				if (ar->refassgnexpr != NULL)
    					return false;
    
    				/*
    				 * Recurse to remaining subexpressions.  Since the array
    				 * subscripts must yield (noncollatable) integers, they won't
    				 * affect the inner_cxt state.
    				 */
    				if (!foreign_expr_walker((Node *) ar->refupperindexpr,
    										 glob_cxt, &inner_cxt))
    					return false;
    				if (!foreign_expr_walker((Node *) ar->reflowerindexpr,
    										 glob_cxt, &inner_cxt))
    					return false;
    				if (!foreign_expr_walker((Node *) ar->refexpr,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * Array subscripting should yield same collation as input,
    				 * but for safety use same logic as for function nodes.
    				 */
    				collation = ar->refcollid;
    				if (collation == InvalidOid)
    					state = FDW_COLLATE_NONE;
    				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
    						 collation == inner_cxt.collation)
    					state = FDW_COLLATE_SAFE;
    				else
    					state = FDW_COLLATE_UNSAFE;
    			}
    			break;
    		case T_FuncExpr:
    			{
    				FuncExpr   *fe = (FuncExpr *) node;
    
    				/*
    				 * If function used by the expression is not built-in, it
    				 * can't be sent to remote because it might have incompatible
    				 * semantics on remote side.
    				 */
    				if (!is_builtin(fe->funcid))
    					return false;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) fe->args,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * If function's input collation is not derived from a foreign
    				 * Var, it can't be sent to remote.
    				 */
    				if (fe->inputcollid == InvalidOid)
    					 /* OK, inputs are all noncollatable */ ;
    				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
    						 fe->inputcollid != inner_cxt.collation)
    					return false;
    
    				/*
    				 * Detect whether node is introducing a collation not derived
    				 * from a foreign Var.	(If so, we just mark it unsafe for now
    				 * rather than immediately returning false, since the parent
    				 * node might not care.)
    				 */
    				collation = fe->funccollid;
    				if (collation == InvalidOid)
    					state = FDW_COLLATE_NONE;
    				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
    						 collation == inner_cxt.collation)
    					state = FDW_COLLATE_SAFE;
    				else
    					state = FDW_COLLATE_UNSAFE;
    			}
    			break;
    		case T_OpExpr:
    		case T_DistinctExpr:	/* struct-equivalent to OpExpr */
    			{
    				OpExpr	   *oe = (OpExpr *) node;
    
    				/*
    				 * Similarly, only built-in operators can be sent to remote.
    				 * (If the operator is, surely its underlying function is
    				 * too.)
    				 */
    				if (!is_builtin(oe->opno))
    					return false;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) oe->args,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * If operator's input collation is not derived from a foreign
    				 * Var, it can't be sent to remote.
    				 */
    				if (oe->inputcollid == InvalidOid)
    					 /* OK, inputs are all noncollatable */ ;
    				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
    						 oe->inputcollid != inner_cxt.collation)
    					return false;
    
    				/* Result-collation handling is same as for functions */
    				collation = oe->opcollid;
    				if (collation == InvalidOid)
    					state = FDW_COLLATE_NONE;
    				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
    						 collation == inner_cxt.collation)
    					state = FDW_COLLATE_SAFE;
    				else
    					state = FDW_COLLATE_UNSAFE;
    			}
    			break;
    		case T_ScalarArrayOpExpr:
    			{
    				ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;
    
    				/*
    				 * Again, only built-in operators can be sent to remote.
    				 */
    				if (!is_builtin(oe->opno))
    					return false;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) oe->args,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * If operator's input collation is not derived from a foreign
    				 * Var, it can't be sent to remote.
    				 */
    				if (oe->inputcollid == InvalidOid)
    					 /* OK, inputs are all noncollatable */ ;
    				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
    						 oe->inputcollid != inner_cxt.collation)
    					return false;
    
    				/* Output is always boolean and so noncollatable. */
    				collation = InvalidOid;
    				state = FDW_COLLATE_NONE;
    			}
    			break;
    		case T_RelabelType:
    			{
    				RelabelType *r = (RelabelType *) node;
    
    				/*
    				 * Recurse to input subexpression.
    				 */
    				if (!foreign_expr_walker((Node *) r->arg,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * RelabelType must not introduce a collation not derived from
    				 * an input foreign Var.
    				 */
    				collation = r->resultcollid;
    				if (collation == InvalidOid)
    					state = FDW_COLLATE_NONE;
    				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
    						 collation == inner_cxt.collation)
    					state = FDW_COLLATE_SAFE;
    				else
    					state = FDW_COLLATE_UNSAFE;
    			}
    			break;
    		case T_BoolExpr:
    			{
    				BoolExpr   *b = (BoolExpr *) node;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) b->args,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/* Output is always boolean and so noncollatable. */
    				collation = InvalidOid;
    				state = FDW_COLLATE_NONE;
    			}
    			break;
    		case T_NullTest:
    			{
    				NullTest   *nt = (NullTest *) node;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) nt->arg,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/* Output is always boolean and so noncollatable. */
    				collation = InvalidOid;
    				state = FDW_COLLATE_NONE;
    			}
    			break;
    		case T_ArrayExpr:
    			{
    				ArrayExpr  *a = (ArrayExpr *) node;
    
    				/*
    				 * Recurse to input subexpressions.
    				 */
    				if (!foreign_expr_walker((Node *) a->elements,
    										 glob_cxt, &inner_cxt))
    					return false;
    
    				/*
    				 * ArrayExpr must not introduce a collation not derived from
    				 * an input foreign Var.
    				 */
    				collation = a->array_collid;
    				if (collation == InvalidOid)
    					state = FDW_COLLATE_NONE;
    				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
    						 collation == inner_cxt.collation)
    					state = FDW_COLLATE_SAFE;
    				else
    					state = FDW_COLLATE_UNSAFE;
    			}
    			break;
    		case T_List:
    			{
    				List	   *l = (List *) node;
    				ListCell   *lc;
    
    				/*
    				 * Recurse to component subexpressions.
    				 */
    				foreach(lc, l)
    				{
    					if (!foreign_expr_walker((Node *) lfirst(lc),
    											 glob_cxt, &inner_cxt))
    						return false;
    				}
    
    				/*
    				 * When processing a list, collation state just bubbles up
    				 * from the list elements.
    				 */
    				collation = inner_cxt.collation;
    				state = inner_cxt.state;
    
    				/* Don't apply exprType() to the list. */
    				check_type = false;
    			}
    			break;
    		default:
    
    			/*
    			 * If it's anything else, assume it's unsafe.  This list can be
    			 * expanded later, but don't forget to add deparse support below.
    			 */
    			return false;
    	}
    
    	/*
    	 * If result type of given expression is not built-in, it can't be sent to
    	 * remote because it might have incompatible semantics on remote side.
    	 */
    	if (check_type && !is_builtin(exprType(node)))
    		return false;
    
    	/*
    	 * Now, merge my collation information into my parent's state.
    	 */
    	if (state > outer_cxt->state)
    	{
    		/* Override previous parent state */
    		outer_cxt->collation = collation;
    		outer_cxt->state = state;
    	}
    	else if (state == outer_cxt->state)
    	{
    		/* Merge, or detect error if there's a collation conflict */
    		switch (state)
    		{
    			case FDW_COLLATE_NONE:
    				/* Nothing + nothing is still nothing */
    				break;
    			case FDW_COLLATE_SAFE:
    				if (collation != outer_cxt->collation)
    				{
    					/*
    					 * Non-default collation always beats default.
    					 */
    					if (outer_cxt->collation == DEFAULT_COLLATION_OID)
    					{
    						/* Override previous parent state */
    						outer_cxt->collation = collation;
    					}
    					else if (collation != DEFAULT_COLLATION_OID)
    					{
    						/*
    						 * Conflict; show state as indeterminate.  We don't
    						 * want to "return false" right away, since parent
    						 * node might not care about collation.
    						 */
    						outer_cxt->state = FDW_COLLATE_UNSAFE;
    					}
    				}
    				break;
    			case FDW_COLLATE_UNSAFE:
    				/* We're still conflicted ... */
    				break;
    		}
    	}
    
    	/* It looks OK */
    	return true;
    }
    
    /*
     * Return true if given object is one of PostgreSQL's built-in objects.
     *
     * We use FirstBootstrapObjectId as the cutoff, so that we only consider
     * objects with hand-assigned OIDs to be "built in", not for instance any
     * function or type defined in the information_schema.
     *
     * Our constraints for dealing with types are tighter than they are for
     * functions or operators: we want to accept only types that are in pg_catalog,
     * else format_type might incorrectly fail to schema-qualify their names.
     * (This could be fixed with some changes to format_type, but for now there's
     * no need.)  Thus we must exclude information_schema types.
     *
     * XXX there is a problem with this, which is that the set of built-in
     * objects expands over time.  Something that is built-in to us might not
     * be known to the remote server, if it's of an older version.  But keeping
     * track of that would be a huge exercise.
     */
    static bool
    is_builtin(Oid oid)
    {
    	return (oid < FirstBootstrapObjectId);
    }
    
    
    /*
     * Construct a simple SELECT statement that retrieves desired columns
     * of the specified foreign table, and append it to "buf".	The output
     * contains just "SELECT ... FROM tablename".
     *
     * We also create an integer List of the columns being retrieved, which is
     * returned to *retrieved_attrs.
     */
    void
    deparseSelectSql(StringInfo buf,
    				 PlannerInfo *root,
    				 RelOptInfo *baserel,
    				 Bitmapset *attrs_used,
    				 List **retrieved_attrs)
    {
    	RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
    	Relation	rel;
    
    	/*
    	 * Core code already has some lock on each rel being planned, so we can
    	 * use NoLock here.
    	 */
    	rel = heap_open(rte->relid, NoLock);
    
    	/*
    	 * Construct SELECT list
    	 */
    	appendStringInfoString(buf, "SELECT ");
    	deparseTargetList(buf, root, baserel->relid, rel, attrs_used,
    					  retrieved_attrs);
    
    	/*
    	 * Construct FROM clause
    	 */
    	appendStringInfoString(buf, " FROM ");
    	deparseRelation(buf, rel);
    
    	heap_close(rel, NoLock);
    }
    
    /*
     * Emit a target list that retrieves the columns specified in attrs_used.
     * This is used for both SELECT and RETURNING targetlists.
     *
     * The tlist text is appended to buf, and we also create an integer List
     * of the columns being retrieved, which is returned to *retrieved_attrs.
     */
    static void
    deparseTargetList(StringInfo buf,
    				  PlannerInfo *root,
    				  Index rtindex,
    				  Relation rel,
    				  Bitmapset *attrs_used,
    				  List **retrieved_attrs)
    {
    	TupleDesc	tupdesc = RelationGetDescr(rel);
    	bool		have_wholerow;
    	bool		first;
    	int			i;
    
    	*retrieved_attrs = NIL;
    
    	/* If there's a whole-row reference, we'll need all the columns. */
    	have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
    								  attrs_used);
    
    	first = true;
    	for (i = 1; i <= tupdesc->natts; i++)
    	{
    		Form_pg_attribute attr = tupdesc->attrs[i - 1];
    
    		/* Ignore dropped attributes. */
    		if (attr->attisdropped)
    			continue;
    
    		if (have_wholerow ||
    			bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
    						  attrs_used))
    		{
    			if (!first)
    				appendStringInfoString(buf, ", ");
    			first = false;
    
    			deparseColumnRef(buf, rtindex, i, root);
    
    			*retrieved_attrs = lappend_int(*retrieved_attrs, i);
    		}
    	}
    
    	/*
    	 * Add ctid if needed.	We currently don't support retrieving any other
    	 * system columns.
    	 */
    	if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
    					  attrs_used))
    	{
    		if (!first)
    			appendStringInfoString(buf, ", ");
    		first = false;
    
    		appendStringInfoString(buf, "ctid");
    
    		*retrieved_attrs = lappend_int(*retrieved_attrs,
    									   SelfItemPointerAttributeNumber);
    	}
    
    	/* Don't generate bad syntax if no undropped columns */
    	if (first)
    		appendStringInfoString(buf, "NULL");
    }
    
    /*
     * Deparse WHERE clauses in given list of RestrictInfos and append them to buf.
     *
     * baserel is the foreign table we're planning for.
     *
     * If no WHERE clause already exists in the buffer, is_first should be true.
     *
     * If params is not NULL, it receives a list of Params and other-relation Vars
     * used in the clauses; these values must be transmitted to the remote server
     * as parameter values.
     *
     * If params is NULL, we're generating the query for EXPLAIN purposes,
     * so Params and other-relation Vars should be replaced by dummy values.
     */
    void
    appendWhereClause(StringInfo buf,
    				  PlannerInfo *root,
    				  RelOptInfo *baserel,
    				  List *exprs,
    				  bool is_first,
    				  List **params)
    {
    	deparse_expr_cxt context;
    	int			nestlevel;
    	ListCell   *lc;
    
    	if (params)
    		*params = NIL;			/* initialize result list to empty */
    
    	/* Set up context struct for recursion */
    	context.root = root;
    	context.foreignrel = baserel;
    	context.buf = buf;
    	context.params_list = params;
    
    	/* Make sure any constants in the exprs are printed portably */
    	nestlevel = set_transmission_modes();
    
    	foreach(lc, exprs)
    	{
    		RestrictInfo *ri = (RestrictInfo *) lfirst(lc);
    
    		/* Connect expressions with "AND" and parenthesize each condition. */
    		if (is_first)
    			appendStringInfoString(buf, " WHERE ");
    		else
    			appendStringInfoString(buf, " AND ");
    
    		appendStringInfoChar(buf, '(');
    		deparseExpr(ri->clause, &context);
    		appendStringInfoChar(buf, ')');
    
    		is_first = false;
    	}
    
    	reset_transmission_modes(nestlevel);
    }
    
    /*
     * deparse remote INSERT statement
     *
     * The statement text is appended to buf, and we also create an integer List
     * of the columns being retrieved by RETURNING (if any), which is returned
     * to *retrieved_attrs.
     */
    void
    deparseInsertSql(StringInfo buf, PlannerInfo *root,
    				 Index rtindex, Relation rel,
    				 List *targetAttrs, List *returningList,
    				 List **retrieved_attrs)
    {
    	AttrNumber	pindex;
    	bool		first;
    	ListCell   *lc;
    
    	appendStringInfoString(buf, "INSERT INTO ");
    	deparseRelation(buf, rel);
    
    	if (targetAttrs)
    	{
    		appendStringInfoChar(buf, '(');
    
    		first = true;
    		foreach(lc, targetAttrs)
    		{
    			int			attnum = lfirst_int(lc);
    
    			if (!first)
    				appendStringInfoString(buf, ", ");
    			first = false;
    
    			deparseColumnRef(buf, rtindex, attnum, root);
    		}
    
    		appendStringInfoString(buf, ") VALUES (");
    
    		pindex = 1;
    		first = true;
    		foreach(lc, targetAttrs)
    		{
    			if (!first)
    				appendStringInfoString(buf, ", ");
    			first = false;
    
    			appendStringInfo(buf, "$%d", pindex);
    			pindex++;
    		}
    
    		appendStringInfoChar(buf, ')');
    	}
    	else
    		appendStringInfoString(buf, " DEFAULT VALUES");
    
    	deparseReturningList(buf, root, rtindex, rel,
    					   rel->trigdesc && rel->trigdesc->trig_insert_after_row,
    						 returningList, retrieved_attrs);
    }
    
    /*
     * deparse remote UPDATE statement
     *
     * The statement text is appended to buf, and we also create an integer List
     * of the columns being retrieved by RETURNING (if any), which is returned
     * to *retrieved_attrs.
     */
    void
    deparseUpdateSql(StringInfo buf, PlannerInfo *root,
    				 Index rtindex, Relation rel,
    				 List *targetAttrs, List *returningList,
    				 List **retrieved_attrs)
    {
    	AttrNumber	pindex;
    	bool		first;
    	ListCell   *lc;
    
    	appendStringInfoString(buf, "UPDATE ");
    	deparseRelation(buf, rel);
    	appendStringInfoString(buf, " SET ");
    
    	pindex = 2;					/* ctid is always the first param */
    	first = true;
    	foreach(lc, targetAttrs)
    	{
    		int			attnum = lfirst_int(lc);
    
    		if (!first)
    			appendStringInfoString(buf, ", ");
    		first = false;
    
    		deparseColumnRef(buf, rtindex, attnum, root);
    		appendStringInfo(buf, " = $%d", pindex);
    		pindex++;
    	}
    	appendStringInfoString(buf, " WHERE ctid = $1");
    
    	deparseReturningList(buf, root, rtindex, rel,
    					   rel->trigdesc && rel->trigdesc->trig_update_after_row,
    						 returningList, retrieved_attrs);
    }
    
    /*
     * deparse remote DELETE statement
     *
     * The statement text is appended to buf, and we also create an integer List
     * of the columns being retrieved by RETURNING (if any), which is returned
     * to *retrieved_attrs.
     */
    void
    deparseDeleteSql(StringInfo buf, PlannerInfo *root,
    				 Index rtindex, Relation rel,
    				 List *returningList,
    				 List **retrieved_attrs)
    {
    	appendStringInfoString(buf, "DELETE FROM ");
    	deparseRelation(buf, rel);
    	appendStringInfoString(buf, " WHERE ctid = $1");
    
    	deparseReturningList(buf, root, rtindex, rel,
    					   rel->trigdesc && rel->trigdesc->trig_delete_after_row,
    						 returningList, retrieved_attrs);
    }
    
    /*
     * Add a RETURNING clause, if needed, to an INSERT/UPDATE/DELETE.
     */
    static void
    deparseReturningList(StringInfo buf, PlannerInfo *root,
    					 Index rtindex, Relation rel,
    					 bool trig_after_row,
    					 List *returningList,
    					 List **retrieved_attrs)
    {
    	Bitmapset  *attrs_used = NULL;
    
    	if (trig_after_row)
    	{
    		/* whole-row reference acquires all non-system columns */
    		attrs_used =
    			bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber);
    	}
    
    	if (returningList != NIL)
    	{
    		/*
    		 * We need the attrs, non-system and system, mentioned in the local
    		 * query's RETURNING list.
    		 */
    		pull_varattnos((Node *) returningList, rtindex,
    					   &attrs_used);
    	}
    
    	if (attrs_used != NULL)
    	{
    		appendStringInfoString(buf, " RETURNING ");
    		deparseTargetList(buf, root, rtindex, rel, attrs_used,
    						  retrieved_attrs);
    	}
    	else
    		*retrieved_attrs = NIL;
    }
    
    /*
     * Construct SELECT statement to acquire size in blocks of given relation.
     *
     * Note: we use local definition of block size, not remote definition.
     * This is perhaps debatable.
     *
     * Note: pg_relation_size() exists in 8.1 and later.
     */
    void
    deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
    {
    	StringInfoData relname;
    
    	/* We'll need the remote relation name as a literal. */
    	initStringInfo(&relname);
    	deparseRelation(&relname, rel);
    
    	appendStringInfoString(buf, "SELECT pg_catalog.pg_relation_size(");
    	deparseStringLiteral(buf, relname.data);
    	appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
    }
    
    /*
     * Construct SELECT statement to acquire sample rows of given relation.
     *
     * SELECT command is appended to buf, and list of columns retrieved
     * is returned to *retrieved_attrs.
     */
    void
    deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
    {
    	Oid			relid = RelationGetRelid(rel);
    	TupleDesc	tupdesc = RelationGetDescr(rel);
    	int			i;
    	char	   *colname;
    	List	   *options;
    	ListCell   *lc;
    	bool		first = true;
    
    	*retrieved_attrs = NIL;
    
    	appendStringInfoString(buf, "SELECT ");
    	for (i = 0; i < tupdesc->natts; i++)
    	{
    		/* Ignore dropped columns. */
    		if (tupdesc->attrs[i]->attisdropped)
    			continue;
    
    		if (!first)
    			appendStringInfoString(buf, ", ");
    		first = false;
    
    		/* Use attribute name or column_name option. */
    		colname = NameStr(tupdesc->attrs[i]->attname);
    		options = GetForeignColumnOptions(relid, i + 1);
    
    		foreach(lc, options)
    		{
    			DefElem    *def = (DefElem *) lfirst(lc);
    
    			if (strcmp(def->defname, "column_name") == 0)
    			{
    				colname = defGetString(def);
    				break;
    			}
    		}
    
    		appendStringInfoString(buf, quote_identifier(colname));
    
    		*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
    	}
    
    	/* Don't generate bad syntax for zero-column relation. */
    	if (first)
    		appendStringInfoString(buf, "NULL");
    
    	/*
    	 * Construct FROM clause
    	 */
    	appendStringInfoString(buf, " FROM ");
    	deparseRelation(buf, rel);
    }
    
    /*
     * Construct name to use for given column, and emit it into buf.
     * If it has a column_name FDW option, use that instead of attribute name.
     */
    static void
    deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root)
    {
    	RangeTblEntry *rte;
    	char	   *colname = NULL;
    	List	   *options;
    	ListCell   *lc;
    
    	/* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
    	Assert(!IS_SPECIAL_VARNO(varno));
    
    	/* Get RangeTblEntry from array in PlannerInfo. */
    	rte = planner_rt_fetch(varno, root);
    
    	/*
    	 * If it's a column of a foreign table, and it has the column_name FDW
    	 * option, use that value.
    	 */
    	options = GetForeignColumnOptions(rte->relid, varattno);
    	foreach(lc, options)
    	{
    		DefElem    *def = (DefElem *) lfirst(lc);
    
    		if (strcmp(def->defname, "column_name") == 0)
    		{
    			colname = defGetString(def);
    			break;
    		}
    	}
    
    	/*
    	 * If it's a column of a regular table or it doesn't have column_name FDW
    	 * option, use attribute name.
    	 */
    	if (colname == NULL)
    		colname = get_relid_attribute_name(rte->relid, varattno);
    
    	appendStringInfoString(buf, quote_identifier(colname));
    }
    
    /*
     * Append remote name of specified foreign table to buf.
     * Use value of table_name FDW option (if any) instead of relation's name.
     * Similarly, schema_name FDW option overrides schema name.
     */
    static void
    deparseRelation(StringInfo buf, Relation rel)
    {
    	ForeignTable *table;
    	const char *nspname = NULL;
    	const char *relname = NULL;
    	ListCell   *lc;
    
    	/* obtain additional catalog information. */
    	table = GetForeignTable(RelationGetRelid(rel));
    
    	/*
    	 * Use value of FDW options if any, instead of the name of object itself.
    	 */
    	foreach(lc, table->options)
    	{
    		DefElem    *def = (DefElem *) lfirst(lc);
    
    		if (strcmp(def->defname, "schema_name") == 0)
    			nspname = defGetString(def);
    		else if (strcmp(def->defname, "table_name") == 0)
    			relname = defGetString(def);
    	}
    
    	/*
    	 * Note: we could skip printing the schema name if it's pg_catalog, but
    	 * that doesn't seem worth the trouble.
    	 */
    	if (nspname == NULL)
    		nspname = get_namespace_name(RelationGetNamespace(rel));
    	if (relname == NULL)
    		relname = RelationGetRelationName(rel);
    
    	appendStringInfo(buf, "%s.%s",
    					 quote_identifier(nspname), quote_identifier(relname));
    }
    
    /*
     * Append a SQL string literal representing "val" to buf.
     */
    static void
    deparseStringLiteral(StringInfo buf, const char *val)
    {
    	const char *valptr;
    
    	/*
    	 * Rather than making assumptions about the remote server's value of
    	 * standard_conforming_strings, always use E'foo' syntax if there are any
    	 * backslashes.  This will fail on remote servers before 8.1, but those
    	 * are long out of support.
    	 */
    	if (strchr(val, '\\') != NULL)
    		appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
    	appendStringInfoChar(buf, '\'');
    	for (valptr = val; *valptr; valptr++)
    	{
    		char		ch = *valptr;
    
    		if (SQL_STR_DOUBLE(ch, true))
    			appendStringInfoChar(buf, ch);
    		appendStringInfoChar(buf, ch);
    	}
    	appendStringInfoChar(buf, '\'');
    }
    
    /*
     * Deparse given expression into context->buf.
     *
     * This function must support all the same node types that foreign_expr_walker
     * accepts.
     *
     * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
     * scheme: anything more complex than a Var, Const, function call or cast
     * should be self-parenthesized.
     */
    static void
    deparseExpr(Expr *node, deparse_expr_cxt *context)
    {
    	if (node == NULL)
    		return;
    
    	switch (nodeTag(node))
    	{
    		case T_Var:
    			deparseVar((Var *) node, context);
    			break;
    		case T_Const:
    			deparseConst((Const *) node, context);
    			break;
    		case T_Param:
    			deparseParam((Param *) node, context);
    			break;
    		case T_ArrayRef:
    			deparseArrayRef((ArrayRef *) node, context);
    			break;
    		case T_FuncExpr:
    			deparseFuncExpr((FuncExpr *) node, context);
    			break;
    		case T_OpExpr:
    			deparseOpExpr((OpExpr *) node, context);
    			break;
    		case T_DistinctExpr:
    			deparseDistinctExpr((DistinctExpr *) node, context);
    			break;
    		case T_ScalarArrayOpExpr:
    			deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
    			break;
    		case T_RelabelType:
    			deparseRelabelType((RelabelType *) node, context);
    			break;
    		case T_BoolExpr:
    			deparseBoolExpr((BoolExpr *) node, context);
    			break;
    		case T_NullTest:
    			deparseNullTest((NullTest *) node, context);
    			break;
    		case T_ArrayExpr:
    			deparseArrayExpr((ArrayExpr *) node, context);
    			break;
    		default:
    			elog(ERROR, "unsupported expression type for deparse: %d",
    				 (int) nodeTag(node));
    			break;
    	}
    }
    
    /*
     * Deparse given Var node into context->buf.
     *
     * If the Var belongs to the foreign relation, just print its remote name.
     * Otherwise, it's effectively a Param (and will in fact be a Param at
     * run time).  Handle it the same way we handle plain Params --- see
     * deparseParam for comments.
     */
    static void
    deparseVar(Var *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    
    	if (node->varno == context->foreignrel->relid &&
    		node->varlevelsup == 0)
    	{
    		/* Var belongs to foreign table */
    		deparseColumnRef(buf, node->varno, node->varattno, context->root);
    	}
    	else
    	{
    		/* Treat like a Param */
    		if (context->params_list)
    		{
    			int			pindex = 0;
    			ListCell   *lc;
    
    			/* find its index in params_list */
    			foreach(lc, *context->params_list)
    			{
    				pindex++;
    				if (equal(node, (Node *) lfirst(lc)))
    					break;
    			}
    			if (lc == NULL)
    			{
    				/* not in list, so add it */
    				pindex++;
    				*context->params_list = lappend(*context->params_list, node);
    			}
    
    			printRemoteParam(pindex, node->vartype, node->vartypmod, context);
    		}
    		else
    		{
    			printRemotePlaceholder(node->vartype, node->vartypmod, context);
    		}
    	}
    }
    
    /*
     * Deparse given constant value into context->buf.
     *
     * This function has to be kept in sync with ruleutils.c's get_const_expr.
     */
    static void
    deparseConst(Const *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	Oid			typoutput;
    	bool		typIsVarlena;
    	char	   *extval;
    	bool		isfloat = false;
    	bool		needlabel;
    
    	if (node->constisnull)
    	{
    		appendStringInfoString(buf, "NULL");
    		appendStringInfo(buf, "::%s",
    						 format_type_with_typemod(node->consttype,
    												  node->consttypmod));
    		return;
    	}
    
    	getTypeOutputInfo(node->consttype,
    					  &typoutput, &typIsVarlena);
    	extval = OidOutputFunctionCall(typoutput, node->constvalue);
    
    	switch (node->consttype)
    	{
    		case INT2OID:
    		case INT4OID:
    		case INT8OID:
    		case OIDOID:
    		case FLOAT4OID:
    		case FLOAT8OID:
    		case NUMERICOID:
    			{
    				/*
    				 * No need to quote unless it's a special value such as 'NaN'.
    				 * See comments in get_const_expr().
    				 */
    				if (strspn(extval, "0123456789+-eE.") == strlen(extval))
    				{
    					if (extval[0] == '+' || extval[0] == '-')
    						appendStringInfo(buf, "(%s)", extval);
    					else
    						appendStringInfoString(buf, extval);
    					if (strcspn(extval, "eE.") != strlen(extval))
    						isfloat = true; /* it looks like a float */
    				}
    				else
    					appendStringInfo(buf, "'%s'", extval);
    			}
    			break;
    		case BITOID:
    		case VARBITOID:
    			appendStringInfo(buf, "B'%s'", extval);
    			break;
    		case BOOLOID:
    			if (strcmp(extval, "t") == 0)
    				appendStringInfoString(buf, "true");
    			else
    				appendStringInfoString(buf, "false");
    			break;
    		default:
    			deparseStringLiteral(buf, extval);
    			break;
    	}
    
    	/*
    	 * Append ::typename unless the constant will be implicitly typed as the
    	 * right type when it is read in.
    	 *
    	 * XXX this code has to be kept in sync with the behavior of the parser,
    	 * especially make_const.
    	 */
    	switch (node->consttype)
    	{
    		case BOOLOID:
    		case INT4OID:
    		case UNKNOWNOID:
    			needlabel = false;
    			break;
    		case NUMERICOID:
    			needlabel = !isfloat || (node->consttypmod >= 0);
    			break;
    		default:
    			needlabel = true;
    			break;
    	}
    	if (needlabel)
    		appendStringInfo(buf, "::%s",
    						 format_type_with_typemod(node->consttype,
    												  node->consttypmod));
    }
    
    /*
     * Deparse given Param node.
     *
     * If we're generating the query "for real", add the Param to
     * context->params_list if it's not already present, and then use its index
     * in that list as the remote parameter number.  During EXPLAIN, there's
     * no need to identify a parameter number.
     */
    static void
    deparseParam(Param *node, deparse_expr_cxt *context)
    {
    	if (context->params_list)
    	{
    		int			pindex = 0;
    		ListCell   *lc;
    
    		/* find its index in params_list */
    		foreach(lc, *context->params_list)
    		{
    			pindex++;
    			if (equal(node, (Node *) lfirst(lc)))
    				break;
    		}
    		if (lc == NULL)
    		{
    			/* not in list, so add it */
    			pindex++;
    			*context->params_list = lappend(*context->params_list, node);
    		}
    
    		printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
    	}
    	else
    	{
    		printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
    	}
    }
    
    /*
     * Deparse an array subscript expression.
     */
    static void
    deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	ListCell   *lowlist_item;
    	ListCell   *uplist_item;
    
    	/* Always parenthesize the expression. */
    	appendStringInfoChar(buf, '(');
    
    	/*
    	 * Deparse referenced array expression first.  If that expression includes
    	 * a cast, we have to parenthesize to prevent the array subscript from
    	 * being taken as typename decoration.	We can avoid that in the typical
    	 * case of subscripting a Var, but otherwise do it.
    	 */
    	if (IsA(node->refexpr, Var))
    		deparseExpr(node->refexpr, context);
    	else
    	{
    		appendStringInfoChar(buf, '(');
    		deparseExpr(node->refexpr, context);
    		appendStringInfoChar(buf, ')');
    	}
    
    	/* Deparse subscript expressions. */
    	lowlist_item = list_head(node->reflowerindexpr);	/* could be NULL */
    	foreach(uplist_item, node->refupperindexpr)
    	{
    		appendStringInfoChar(buf, '[');
    		if (lowlist_item)
    		{
    			deparseExpr(lfirst(lowlist_item), context);
    			appendStringInfoChar(buf, ':');
    			lowlist_item = lnext(lowlist_item);
    		}
    		deparseExpr(lfirst(uplist_item), context);
    		appendStringInfoChar(buf, ']');
    	}
    
    	appendStringInfoChar(buf, ')');
    }
    
    /*
     * Deparse a function call.
     */
    static void
    deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	HeapTuple	proctup;
    	Form_pg_proc procform;
    	const char *proname;
    	bool		use_variadic;
    	bool		first;
    	ListCell   *arg;
    
    	/*
    	 * If the function call came from an implicit coercion, then just show the
    	 * first argument.
    	 */
    	if (node->funcformat == COERCE_IMPLICIT_CAST)
    	{
    		deparseExpr((Expr *) linitial(node->args), context);
    		return;
    	}
    
    	/*
    	 * If the function call came from a cast, then show the first argument
    	 * plus an explicit cast operation.
    	 */
    	if (node->funcformat == COERCE_EXPLICIT_CAST)
    	{
    		Oid			rettype = node->funcresulttype;
    		int32		coercedTypmod;
    
    		/* Get the typmod if this is a length-coercion function */
    		(void) exprIsLengthCoercion((Node *) node, &coercedTypmod);
    
    		deparseExpr((Expr *) linitial(node->args), context);
    		appendStringInfo(buf, "::%s",
    						 format_type_with_typemod(rettype, coercedTypmod));
    		return;
    	}
    
    	/*
    	 * Normal function: display as proname(args).
    	 */
    	proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(node->funcid));
    	if (!HeapTupleIsValid(proctup))
    		elog(ERROR, "cache lookup failed for function %u", node->funcid);
    	procform = (Form_pg_proc) GETSTRUCT(proctup);
    
    	/* Check if need to print VARIADIC (cf. ruleutils.c) */
    	use_variadic = node->funcvariadic;
    
    	/* Print schema name only if it's not pg_catalog */
    	if (procform->pronamespace != PG_CATALOG_NAMESPACE)
    	{
    		const char *schemaname;
    
    		schemaname = get_namespace_name(procform->pronamespace);
    		appendStringInfo(buf, "%s.", quote_identifier(schemaname));
    	}
    
    	/* Deparse the function name ... */
    	proname = NameStr(procform->proname);
    	appendStringInfo(buf, "%s(", quote_identifier(proname));
    	/* ... and all the arguments */
    	first = true;
    	foreach(arg, node->args)
    	{
    		if (!first)
    			appendStringInfoString(buf, ", ");
    		if (use_variadic && lnext(arg) == NULL)
    			appendStringInfoString(buf, "VARIADIC ");
    		deparseExpr((Expr *) lfirst(arg), context);
    		first = false;
    	}
    	appendStringInfoChar(buf, ')');
    
    	ReleaseSysCache(proctup);
    }
    
    /*
     * Deparse given operator expression.	To avoid problems around
     * priority of operations, we always parenthesize the arguments.
     */
    static void
    deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	HeapTuple	tuple;
    	Form_pg_operator form;
    	char		oprkind;
    	ListCell   *arg;
    
    	/* Retrieve information about the operator from system catalog. */
    	tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    	if (!HeapTupleIsValid(tuple))
    		elog(ERROR, "cache lookup failed for operator %u", node->opno);
    	form = (Form_pg_operator) GETSTRUCT(tuple);
    	oprkind = form->oprkind;
    
    	/* Sanity check. */
    	Assert((oprkind == 'r' && list_length(node->args) == 1) ||
    		   (oprkind == 'l' && list_length(node->args) == 1) ||
    		   (oprkind == 'b' && list_length(node->args) == 2));
    
    	/* Always parenthesize the expression. */
    	appendStringInfoChar(buf, '(');
    
    	/* Deparse left operand. */
    	if (oprkind == 'r' || oprkind == 'b')
    	{
    		arg = list_head(node->args);
    		deparseExpr(lfirst(arg), context);
    		appendStringInfoChar(buf, ' ');
    	}
    
    	/* Deparse operator name. */
    	deparseOperatorName(buf, form);
    
    	/* Deparse right operand. */
    	if (oprkind == 'l' || oprkind == 'b')
    	{
    		arg = list_tail(node->args);
    		appendStringInfoChar(buf, ' ');
    		deparseExpr(lfirst(arg), context);
    	}
    
    	appendStringInfoChar(buf, ')');
    
    	ReleaseSysCache(tuple);
    }
    
    /*
     * Print the name of an operator.
     */
    static void
    deparseOperatorName(StringInfo buf, Form_pg_operator opform)
    {
    	char	   *opname;
    
    	/* opname is not a SQL identifier, so we should not quote it. */
    	opname = NameStr(opform->oprname);
    
    	/* Print schema name only if it's not pg_catalog */
    	if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
    	{
    		const char *opnspname;
    
    		opnspname = get_namespace_name(opform->oprnamespace);
    		/* Print fully qualified operator name. */
    		appendStringInfo(buf, "OPERATOR(%s.%s)",
    						 quote_identifier(opnspname), opname);
    	}
    	else
    	{
    		/* Just print operator name. */
    		appendStringInfoString(buf, opname);
    	}
    }
    
    /*
     * Deparse IS DISTINCT FROM.
     */
    static void
    deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    
    	Assert(list_length(node->args) == 2);
    
    	appendStringInfoChar(buf, '(');
    	deparseExpr(linitial(node->args), context);
    	appendStringInfoString(buf, " IS DISTINCT FROM ");
    	deparseExpr(lsecond(node->args), context);
    	appendStringInfoChar(buf, ')');
    }
    
    /*
     * Deparse given ScalarArrayOpExpr expression.	To avoid problems
     * around priority of operations, we always parenthesize the arguments.
     */
    static void
    deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	HeapTuple	tuple;
    	Form_pg_operator form;
    	Expr	   *arg1;
    	Expr	   *arg2;
    
    	/* Retrieve information about the operator from system catalog. */
    	tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    	if (!HeapTupleIsValid(tuple))
    		elog(ERROR, "cache lookup failed for operator %u", node->opno);
    	form = (Form_pg_operator) GETSTRUCT(tuple);
    
    	/* Sanity check. */
    	Assert(list_length(node->args) == 2);
    
    	/* Always parenthesize the expression. */
    	appendStringInfoChar(buf, '(');
    
    	/* Deparse left operand. */
    	arg1 = linitial(node->args);
    	deparseExpr(arg1, context);
    	appendStringInfoChar(buf, ' ');
    
    	/* Deparse operator name plus decoration. */
    	deparseOperatorName(buf, form);
    	appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");
    
    	/* Deparse right operand. */
    	arg2 = lsecond(node->args);
    	deparseExpr(arg2, context);
    
    	appendStringInfoChar(buf, ')');
    
    	/* Always parenthesize the expression. */
    	appendStringInfoChar(buf, ')');
    
    	ReleaseSysCache(tuple);
    }
    
    /*
     * Deparse a RelabelType (binary-compatible cast) node.
     */
    static void
    deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
    {
    	deparseExpr(node->arg, context);
    	if (node->relabelformat != COERCE_IMPLICIT_CAST)
    		appendStringInfo(context->buf, "::%s",
    						 format_type_with_typemod(node->resulttype,
    												  node->resulttypmod));
    }
    
    /*
     * Deparse a BoolExpr node.
     *
     * Note: by the time we get here, AND and OR expressions have been flattened
     * into N-argument form, so we'd better be prepared to deal with that.
     */
    static void
    deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	const char *op = NULL;		/* keep compiler quiet */
    	bool		first;
    	ListCell   *lc;
    
    	switch (node->boolop)
    	{
    		case AND_EXPR:
    			op = "AND";
    			break;
    		case OR_EXPR:
    			op = "OR";
    			break;
    		case NOT_EXPR:
    			appendStringInfoString(buf, "(NOT ");
    			deparseExpr(linitial(node->args), context);
    			appendStringInfoChar(buf, ')');
    			return;
    	}
    
    	appendStringInfoChar(buf, '(');
    	first = true;
    	foreach(lc, node->args)
    	{
    		if (!first)
    			appendStringInfo(buf, " %s ", op);
    		deparseExpr((Expr *) lfirst(lc), context);
    		first = false;
    	}
    	appendStringInfoChar(buf, ')');
    }
    
    /*
     * Deparse IS [NOT] NULL expression.
     */
    static void
    deparseNullTest(NullTest *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    
    	appendStringInfoChar(buf, '(');
    	deparseExpr(node->arg, context);
    	if (node->nulltesttype == IS_NULL)
    		appendStringInfoString(buf, " IS NULL)");
    	else
    		appendStringInfoString(buf, " IS NOT NULL)");
    }
    
    /*
     * Deparse ARRAY[...] construct.
     */
    static void
    deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	bool		first = true;
    	ListCell   *lc;
    
    	appendStringInfoString(buf, "ARRAY[");
    	foreach(lc, node->elements)
    	{
    		if (!first)
    			appendStringInfoString(buf, ", ");
    		deparseExpr(lfirst(lc), context);
    		first = false;
    	}
    	appendStringInfoChar(buf, ']');
    
    	/* If the array is empty, we need an explicit cast to the array type. */
    	if (node->elements == NIL)
    		appendStringInfo(buf, "::%s",
    						 format_type_with_typemod(node->array_typeid, -1));
    }
    
    /*
     * Print the representation of a parameter to be sent to the remote side.
     *
     * Note: we always label the Param's type explicitly rather than relying on
     * transmitting a numeric type OID in PQexecParams().  This allows us to
     * avoid assuming that types have the same OIDs on the remote side as they
     * do locally --- they need only have the same names.
     */
    static void
    printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
    				 deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	char	   *ptypename = format_type_with_typemod(paramtype, paramtypmod);
    
    	appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
    }
    
    /*
     * Print the representation of a placeholder for a parameter that will be
     * sent to the remote side at execution time.
     *
     * This is used when we're just trying to EXPLAIN the remote query.
     * We don't have the actual value of the runtime parameter yet, and we don't
     * want the remote planner to generate a plan that depends on such a value
     * anyway.	Thus, we can't do something simple like "$1::paramtype".
     * Instead, we emit "((SELECT null::paramtype)::paramtype)".
     * In all extant versions of Postgres, the planner will see that as an unknown
     * constant value, which is what we want.  This might need adjustment if we
     * ever make the planner flatten scalar subqueries.  Note: the reason for the
     * apparently useless outer cast is to ensure that the representation as a
     * whole will be parsed as an a_expr and not a select_with_parens; the latter
     * would do the wrong thing in the context "x = ANY(...)".
     */
    static void
    printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
    					   deparse_expr_cxt *context)
    {
    	StringInfo	buf = context->buf;
    	char	   *ptypename = format_type_with_typemod(paramtype, paramtypmod);
    
    	appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
    }