/*-------------------------------------------------------------------------
*
* parse_clause.c
* handle clauses in parser
*
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.82 2001/08/09 18:28:17 petere Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "nodes/makefuncs.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse.h"
#include "parser/parsetree.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parse_target.h"
#include "parser/parse_type.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#define ORDER_CLAUSE 0
#define GROUP_CLAUSE 1
#define DISTINCT_ON_CLAUSE 2
static char *clauseText[] = {"ORDER BY", "GROUP BY", "DISTINCT ON"};
static void extractUniqueColumns(List *common_colnames,
List *src_colnames, List *src_colvars,
List **res_colnames, List **res_colvars);
static Node *transformJoinUsingClause(ParseState *pstate,
List *leftVars, List *rightVars);
static Node *transformJoinOnClause(ParseState *pstate, JoinExpr *j,
List *containedRels);
static RangeTblRef *transformTableEntry(ParseState *pstate, RangeVar *r);
static RangeTblRef *transformRangeSubselect(ParseState *pstate,
RangeSubselect *r);
static Node *transformFromClauseItem(ParseState *pstate, Node *n,
List **containedRels);
static TargetEntry *findTargetlistEntry(ParseState *pstate, Node *node,
List *tlist, int clause);
static List *addTargetToSortList(TargetEntry *tle, List *sortlist,
List *targetlist, char *opname);
static bool exprIsInSortList(Node *expr, List *sortList, List *targetList);
/*
* transformFromClause -
* Process the FROM clause and add items to the query's range table,
* joinlist, and namespace.
*
* Note: we assume that pstate's p_rtable, p_joinlist, and p_namespace lists
* were initialized to NIL when the pstate was created. We will add onto
* any entries already present --- this is needed for rule processing, as
* well as for UPDATE and DELETE.
*
* The range table may grow still further when we transform the expressions
* in the query's quals and target list. (This is possible because in
* POSTQUEL, we allowed references to relations not specified in the
* from-clause. PostgreSQL keeps this extension to standard SQL.)
*/
void
transformFromClause(ParseState *pstate, List *frmList)
{
List *fl;
/*
* The grammar will have produced a list of RangeVars,
* RangeSubselects, and/or JoinExprs. Transform each one (possibly
* adding entries to the rtable), check for duplicate refnames, and
* then add it to the joinlist and namespace.
*/
foreach(fl, frmList)
{
Node *n = lfirst(fl);
List *containedRels;
n = transformFromClauseItem(pstate, n, &containedRels);
checkNameSpaceConflicts(pstate, (Node *) pstate->p_namespace, n);
pstate->p_joinlist = lappend(pstate->p_joinlist, n);
pstate->p_namespace = lappend(pstate->p_namespace, n);
}
}
/*
* setTargetTable
* Add the target relation of INSERT/UPDATE/DELETE to the range table,
* and make the special links to it in the ParseState.
*
* We also open the target relation and acquire a write lock on it.
* This must be done before processing the FROM list, in case the target
* is also mentioned as a source relation --- we want to be sure to grab
* the write lock before any read lock.
*
* If alsoSource is true, add the target to the query's joinlist and
* namespace. For INSERT, we don't want the target to be joined to;
* it's a destination of tuples, not a source. For UPDATE/DELETE,
* we do need to scan or join the target. (NOTE: we do not bother
* to check for namespace conflict; we assume that the namespace was
* initially empty in these cases.)
*
* Returns the rangetable index of the target relation.
*/
int
setTargetTable(ParseState *pstate, char *relname,
bool inh, bool alsoSource)
{
RangeTblEntry *rte;
int rtindex;
/* Close old target; this could only happen for multi-action rules */
if (pstate->p_target_relation != NULL)
heap_close(pstate->p_target_relation, NoLock);
/*
* Open target rel and grab suitable lock (which we will hold till end
* of transaction).
*
* analyze.c will eventually do the corresponding heap_close(), but *not*
* release the lock.
*/
pstate->p_target_relation = heap_openr(relname, RowExclusiveLock);
/*
* Now build an RTE.
*/
rte = addRangeTableEntry(pstate, relname, NULL, inh, false);
pstate->p_target_rangetblentry = rte;
/* assume new rte is at end */
rtindex = length(pstate->p_rtable);
Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
/*
* Override addRangeTableEntry's default checkForRead, and instead
* mark target table as requiring write access.
*
* If we find an explicit reference to the rel later during parse
* analysis, scanRTEForColumn will change checkForRead to 'true'
* again. That can't happen for INSERT but it is possible for UPDATE
* and DELETE.
*/
rte->checkForRead = false;
rte->checkForWrite = true;
/*
* If UPDATE/DELETE, add table to joinlist and namespace.
*/
if (alsoSource)
addRTEtoQuery(pstate, rte, true, true);
return rtindex;
}
/*
* Simplify InhOption (yes/no/default) into boolean yes/no.
*
* The reason we do things this way is that we don't want to examine the
* SQL_inheritance option flag until parse_analyze is run. Otherwise,
* we'd do the wrong thing with query strings that intermix SET commands
* with queries.
*/
bool
interpretInhOption(InhOption inhOpt)
{
switch (inhOpt)
{
case INH_NO:
return false;
case INH_YES:
return true;
case INH_DEFAULT:
return SQL_inheritance;
}
elog(ERROR, "Bogus InhOption value");
return false; /* keep compiler quiet */
}
/*
* Extract all not-in-common columns from column lists of a source table
*/
static void
extractUniqueColumns(List *common_colnames,
List *src_colnames, List *src_colvars,
List **res_colnames, List **res_colvars)
{
List *new_colnames = NIL;
List *new_colvars = NIL;
List *lnames,
*lvars = src_colvars;
foreach(lnames, src_colnames)
{
char *colname = strVal(lfirst(lnames));
bool match = false;
List *cnames;
foreach(cnames, common_colnames)
{
char *ccolname = strVal(lfirst(cnames));
if (strcmp(colname, ccolname) == 0)
{
match = true;
break;
}
}
if (!match)
{
new_colnames = lappend(new_colnames, lfirst(lnames));
new_colvars = lappend(new_colvars, lfirst(lvars));
}
lvars = lnext(lvars);
}
*res_colnames = new_colnames;
*res_colvars = new_colvars;
}
/* transformJoinUsingClause()
* Build a complete ON clause from a partially-transformed USING list.
* We are given lists of nodes representing left and right match columns.
* Result is a transformed qualification expression.
*/
static Node *
transformJoinUsingClause(ParseState *pstate, List *leftVars, List *rightVars)
{
Node *result = NULL;
List *lvars,
*rvars = rightVars;
/*
* We cheat a little bit here by building an untransformed operator
* tree whose leaves are the already-transformed Vars. This is OK
* because transformExpr() won't complain about already-transformed
* subnodes.
*/
foreach(lvars, leftVars)
{
Node *lvar = (Node *) lfirst(lvars);
Node *rvar = (Node *) lfirst(rvars);
A_Expr *e;
e = makeNode(A_Expr);
e->oper = OP;
e->opname = "=";
e->lexpr = copyObject(lvar);
e->rexpr = copyObject(rvar);
if (result == NULL)
result = (Node *) e;
else
{
A_Expr *a = makeNode(A_Expr);
a->oper = AND;
a->opname = NULL;
a->lexpr = result;
a->rexpr = (Node *) e;
result = (Node *) a;
}
rvars = lnext(rvars);
}
/*
* Since the references are already Vars, and are certainly from the
* input relations, we don't have to go through the same pushups that
* transformJoinOnClause() does. Just invoke transformExpr() to fix
* up the operators, and we're done.
*/
result = transformExpr(pstate, result, EXPR_COLUMN_FIRST);
/*
* We expect the result to yield bool directly, otherwise complain.
* We could try coerce_to_boolean() here, but it seems likely that an
* "=" operator that doesn't return bool is wrong anyway.
*/
if (exprType(result) != BOOLOID)
elog(ERROR, "JOIN/USING clause must return type boolean, not type %s",
format_type_be(exprType(result)));
return result;
} /* transformJoinUsingClause() */
/* transformJoinOnClause()
* Transform the qual conditions for JOIN/ON.
* Result is a transformed qualification expression.
*/
static Node *
transformJoinOnClause(ParseState *pstate, JoinExpr *j,
List *containedRels)
{
Node *result;
List *save_namespace;
List *clause_varnos,
*l;
/*
* This is a tad tricky, for two reasons. First, the namespace that
* the join expression should see is just the two subtrees of the JOIN
* plus any outer references from upper pstate levels. So,
* temporarily set this pstate's namespace accordingly. (We need not
* check for refname conflicts, because transformFromClauseItem()
* already did.) NOTE: this code is OK only because the ON clause
* can't legally alter the namespace by causing implicit relation refs
* to be added.
*/
save_namespace = pstate->p_namespace;
pstate->p_namespace = makeList2(j->larg, j->rarg);
/* This part is just like transformWhereClause() */
result = transformExpr(pstate, j->quals, EXPR_COLUMN_FIRST);
if (! coerce_to_boolean(pstate, &result))
elog(ERROR, "JOIN/ON clause must return type boolean, not type %s",
format_type_be(exprType(result)));
pstate->p_namespace = save_namespace;
/*
* Second, we need to check that the ON condition doesn't refer to any
* rels outside the input subtrees of the JOIN. It could do that
* despite our hack on the namespace if it uses fully-qualified names.
* So, grovel through the transformed clause and make sure there are
* no bogus references. (Outer references are OK, and are ignored
* here.)
*/
clause_varnos = pull_varnos(result);
foreach(l, clause_varnos)
{
int varno = lfirsti(l);
if (!intMember(varno, containedRels))
{
elog(ERROR, "JOIN/ON clause refers to \"%s\", which is not part of JOIN",
rt_fetch(varno, pstate->p_rtable)->eref->relname);
}
}
freeList(clause_varnos);
return result;
}
/*
* transformTableEntry --- transform a RangeVar (simple relation reference)
*/
static RangeTblRef *
transformTableEntry(ParseState *pstate, RangeVar *r)
{
char *relname = r->relname;
RangeTblEntry *rte;
RangeTblRef *rtr;
/*
* mark this entry to indicate it comes from the FROM clause. In SQL,
* the target list can only refer to range variables specified in the
* from clause but we follow the more powerful POSTQUEL semantics and
* automatically generate the range variable if not specified. However
* there are times we need to know whether the entries are legitimate.
*/
rte = addRangeTableEntry(pstate, relname, r->name,
interpretInhOption(r->inhOpt), true);
/*
* We create a RangeTblRef, but we do not add it to the joinlist or
* namespace; our caller must do that if appropriate.
*/
rtr = makeNode(RangeTblRef);
/* assume new rte is at end */
rtr->rtindex = length(pstate->p_rtable);
Assert(rte == rt_fetch(rtr->rtindex, pstate->p_rtable));
return rtr;
}
/*
* transformRangeSubselect --- transform a sub-SELECT appearing in FROM
*/
static RangeTblRef *
transformRangeSubselect(ParseState *pstate, RangeSubselect *r)
{
List *save_namespace;
List *parsetrees;
Query *query;
RangeTblEntry *rte;
RangeTblRef *rtr;
/*
* We require user to supply an alias for a subselect, per SQL92. To
* relax this, we'd have to be prepared to gin up a unique alias for
* an unlabeled subselect.
*/
if (r->name == NULL)
elog(ERROR, "sub-select in FROM must have an alias");
/*
* Analyze and transform the subquery. This is a bit tricky because
* we don't want the subquery to be able to see any FROM items already
* created in the current query (per SQL92, the scope of a FROM item
* does not include other FROM items). But it does need to be able to
* see any further-up parent states, so we can't just pass a null
* parent pstate link. So, temporarily make the current query level
* have an empty namespace.
*/
save_namespace = pstate->p_namespace;
pstate->p_namespace = NIL;
parsetrees = parse_analyze(r->subquery, pstate);
pstate->p_namespace = save_namespace;
/*
* Check that we got something reasonable. Some of these conditions
* are probably impossible given restrictions of the grammar, but
* check 'em anyway.
*/
if (length(parsetrees) != 1)
elog(ERROR, "Unexpected parse analysis result for subselect in FROM");
query = (Query *) lfirst(parsetrees);
if (query == NULL || !IsA(query, Query))
elog(ERROR, "Unexpected parse analysis result for subselect in FROM");
if (query->commandType != CMD_SELECT)
elog(ERROR, "Expected SELECT query from subselect in FROM");
if (query->resultRelation != 0 || query->into != NULL || query->isPortal)
elog(ERROR, "Subselect in FROM may not have SELECT INTO");
/*
* OK, build an RTE for the subquery.
*/
rte = addRangeTableEntryForSubquery(pstate, query, r->name, true);
/*
* We create a RangeTblRef, but we do not add it to the joinlist or
* namespace; our caller must do that if appropriate.
*/
rtr = makeNode(RangeTblRef);
/* assume new rte is at end */
rtr->rtindex = length(pstate->p_rtable);
Assert(rte == rt_fetch(rtr->rtindex, pstate->p_rtable));
return rtr;
}
/*
* transformFromClauseItem -
* Transform a FROM-clause item, adding any required entries to the
* range table list being built in the ParseState, and return the
* transformed item ready to include in the joinlist and namespace.
* This routine can recurse to handle SQL92 JOIN expressions.
*
* Aside from the primary return value (the transformed joinlist item)
* this routine also returns an integer list of the rangetable indexes
* of all the base relations represented in the joinlist item. This
* list is needed for checking JOIN/ON conditions in higher levels.
*/
static Node *
transformFromClauseItem(ParseState *pstate, Node *n, List **containedRels)
{
if (IsA(n, RangeVar))
{
/* Plain relation reference */
RangeTblRef *rtr;
rtr = transformTableEntry(pstate, (RangeVar *) n);
*containedRels = makeListi1(rtr->rtindex);
return (Node *) rtr;
}
else if (IsA(n, RangeSubselect))
{
/* sub-SELECT is like a plain relation */
RangeTblRef *rtr;
rtr = transformRangeSubselect(pstate, (RangeSubselect *) n);
*containedRels = makeListi1(rtr->rtindex);
return (Node *) rtr;
}
else if (IsA(n, JoinExpr))
{
/* A newfangled join expression */
JoinExpr *j = (JoinExpr *) n;
List *l_containedRels,
*r_containedRels,
*l_colnames,
*r_colnames,
*res_colnames,
*l_colvars,
*r_colvars,
*res_colvars;
/*
* Recursively process the left and right subtrees
*/
j->larg = transformFromClauseItem(pstate, j->larg, &l_containedRels);
j->rarg = transformFromClauseItem(pstate, j->rarg, &r_containedRels);
/*
* Generate combined list of relation indexes
*/
*containedRels = nconc(l_containedRels, r_containedRels);
/*
* Check for conflicting refnames in left and right subtrees. Must
* do this because higher levels will assume I hand back a self-
* consistent namespace subtree.
*/
checkNameSpaceConflicts(pstate, j->larg, j->rarg);
/*
* Extract column name and var lists from both subtrees
*/
if (IsA(j->larg, JoinExpr))
{
/* Make a copy of the subtree's lists so we can modify! */
l_colnames = copyObject(((JoinExpr *) j->larg)->colnames);
l_colvars = copyObject(((JoinExpr *) j->larg)->colvars);
}
else
{
RangeTblEntry *rte;
Assert(IsA(j->larg, RangeTblRef));
rte = rt_fetch(((RangeTblRef *) j->larg)->rtindex,
pstate->p_rtable);
expandRTE(pstate, rte, &l_colnames, &l_colvars);
/* expandRTE returns new lists, so no need for copyObject */
}
if (IsA(j->rarg, JoinExpr))
{
/* Make a copy of the subtree's lists so we can modify! */
r_colnames = copyObject(((JoinExpr *) j->rarg)->colnames);
r_colvars = copyObject(((JoinExpr *) j->rarg)->colvars);
}
else
{
RangeTblEntry *rte;
Assert(IsA(j->rarg, RangeTblRef));
rte = rt_fetch(((RangeTblRef *) j->rarg)->rtindex,
pstate->p_rtable);
expandRTE(pstate, rte, &r_colnames, &r_colvars);
/* expandRTE returns new lists, so no need for copyObject */
}
/*
* Natural join does not explicitly specify columns; must generate
* columns to join. Need to run through the list of columns from
* each table or join result and match up the column names. Use
* the first table, and check every column in the second table for
* a match. (We'll check that the matches were unique later on.)
* The result of this step is a list of column names just like an
* explicitly-written USING list.
*/
if (j->isNatural)
{
List *rlist = NIL;
List *lx,
*rx;
Assert(j->using == NIL); /* shouldn't have USING() too */
foreach(lx, l_colnames)
{
char *l_colname = strVal(lfirst(lx));
Value *m_name = NULL;
foreach(rx, r_colnames)
{
char *r_colname = strVal(lfirst(rx));
if (strcmp(l_colname, r_colname) == 0)
{
m_name = makeString(l_colname);
break;
}
}
/* matched a right column? then keep as join column... */
if (m_name != NULL)
rlist = lappend(rlist, m_name);
}
j->using = rlist;
}
/*
* Now transform the join qualifications, if any.
*/
res_colnames = NIL;
res_colvars = NIL;
if (j->using)
{
/*
* JOIN/USING (or NATURAL JOIN, as transformed above).
* Transform the list into an explicit ON-condition, and
* generate a list of result columns.
*/
List *ucols = j->using;
List *l_usingvars = NIL;
List *r_usingvars = NIL;
List *ucol;
Assert(j->quals == NULL); /* shouldn't have ON() too */
foreach(ucol, ucols)
{
char *u_colname = strVal(lfirst(ucol));
List *col;
Node *l_colvar,
*r_colvar,
*colvar;
int ndx;
int l_index = -1;
int r_index = -1;
ndx = 0;
foreach(col, l_colnames)
{
char *l_colname = strVal(lfirst(col));
if (strcmp(l_colname, u_colname) == 0)
{
if (l_index >= 0)
elog(ERROR, "Common column name \"%s\" appears more than once in left table", u_colname);
l_index = ndx;
}
ndx++;
}
if (l_index < 0)
elog(ERROR, "JOIN/USING column \"%s\" not found in left table",
u_colname);
ndx = 0;
foreach(col, r_colnames)
{
char *r_colname = strVal(lfirst(col));
if (strcmp(r_colname, u_colname) == 0)
{
if (r_index >= 0)
elog(ERROR, "Common column name \"%s\" appears more than once in right table", u_colname);
r_index = ndx;
}
ndx++;
}
if (r_index < 0)
elog(ERROR, "JOIN/USING column \"%s\" not found in right table",
u_colname);
l_colvar = nth(l_index, l_colvars);
l_usingvars = lappend(l_usingvars, l_colvar);
r_colvar = nth(r_index, r_colvars);
r_usingvars = lappend(r_usingvars, r_colvar);
res_colnames = lappend(res_colnames,
nth(l_index, l_colnames));
switch (j->jointype)
{
case JOIN_INNER:
case JOIN_LEFT:
colvar = l_colvar;
break;
case JOIN_RIGHT:
colvar = r_colvar;
break;
default:
{
/* Need COALESCE(l_colvar, r_colvar) */
CaseExpr *c = makeNode(CaseExpr);
CaseWhen *w = makeNode(CaseWhen);
NullTest *n = makeNode(NullTest);
n->arg = l_colvar;
n->nulltesttype = IS_NOT_NULL;
w->expr = (Node *) n;
w->result = l_colvar;
c->args = makeList1(w);
c->defresult = r_colvar;
colvar = transformExpr(pstate, (Node *) c,
EXPR_COLUMN_FIRST);
break;
}
}
res_colvars = lappend(res_colvars, colvar);
}
j->quals = transformJoinUsingClause(pstate,
l_usingvars,
r_usingvars);
}
else if (j->quals)
{
/* User-written ON-condition; transform it */
j->quals = transformJoinOnClause(pstate, j, *containedRels);
}
else
{
/* CROSS JOIN: no quals */
}
/* Add remaining columns from each side to the output columns */
extractUniqueColumns(res_colnames,
l_colnames, l_colvars,
&l_colnames, &l_colvars);
extractUniqueColumns(res_colnames,
r_colnames, r_colvars,
&r_colnames, &r_colvars);
res_colnames = nconc(res_colnames, l_colnames);
res_colvars = nconc(res_colvars, l_colvars);
res_colnames = nconc(res_colnames, r_colnames);
res_colvars = nconc(res_colvars, r_colvars);
/*
* Process alias (AS clause), if any.
*/
if (j->alias)
{
/*
* If a column alias list is specified, substitute the alias
* names into my output-column list
*/
if (j->alias->attrs != NIL)
{
if (length(j->alias->attrs) != length(res_colnames))
elog(ERROR, "Column alias list for \"%s\" has wrong number of entries (need %d)",
j->alias->relname, length(res_colnames));
res_colnames = j->alias->attrs;
}
}
j->colnames = res_colnames;
j->colvars = res_colvars;
return (Node *) j;
}
else
elog(ERROR, "transformFromClauseItem: unexpected node (internal error)"
"\n\t%s", nodeToString(n));
return NULL; /* can't get here, just keep compiler
* quiet */
}
/*
* transformWhereClause -
* transforms the qualification and make sure it is of type Boolean
*/
Node *
transformWhereClause(ParseState *pstate, Node *clause)
{
Node *qual;
if (clause == NULL)
return NULL;
qual = transformExpr(pstate, clause, EXPR_COLUMN_FIRST);
if (! coerce_to_boolean(pstate, &qual))
elog(ERROR, "WHERE clause must return type boolean, not type %s",
format_type_be(exprType(qual)));
return qual;
}
/*
* findTargetlistEntry -
* Returns the targetlist entry matching the given (untransformed) node.
* If no matching entry exists, one is created and appended to the target
* list as a "resjunk" node.
*
* node the ORDER BY, GROUP BY, or DISTINCT ON expression to be matched
* tlist the existing target list (NB: this will never be NIL, which is a
* good thing since we'd be unable to append to it if it were...)
* clause identifies clause type being processed.
*/
static TargetEntry *
findTargetlistEntry(ParseState *pstate, Node *node, List *tlist, int clause)
{
TargetEntry *target_result = NULL;
List *tl;
Node *expr;
/*----------
* Handle two special cases as mandated by the SQL92 spec:
*
* 1. Bare ColumnName (no qualifier or subscripts)
* For a bare identifier, we search for a matching column name
* in the existing target list. Multiple matches are an error
* unless they refer to identical values; for example,
* we allow SELECT a, a FROM table ORDER BY a
* but not SELECT a AS b, b FROM table ORDER BY b
* If no match is found, we fall through and treat the identifier
* as an expression.
* For GROUP BY, it is incorrect to match the grouping item against
* targetlist entries: according to SQL92, an identifier in GROUP BY
* is a reference to a column name exposed by FROM, not to a target
* list column. However, many implementations (including pre-7.0
* PostgreSQL) accept this anyway. So for GROUP BY, we look first
* to see if the identifier matches any FROM column name, and only
* try for a targetlist name if it doesn't. This ensures that we
* adhere to the spec in the case where the name could be both.
* DISTINCT ON isn't in the standard, so we can do what we like there;
* we choose to make it work like ORDER BY, on the rather flimsy
* grounds that ordinary DISTINCT works on targetlist entries.
*
* 2. IntegerConstant
* This means to use the n'th item in the existing target list.
* Note that it would make no sense to order/group/distinct by an
* actual constant, so this does not create a conflict with our
* extension to order/group by an expression.
* GROUP BY column-number is not allowed by SQL92, but since
* the standard has no other behavior defined for this syntax,
* we may as well accept this common extension.
*
* Note that pre-existing resjunk targets must not be used in either case,
* since the user didn't write them in his SELECT list.
*
* If neither special case applies, fall through to treat the item as
* an expression.
*----------
*/
if (IsA(node, Ident) && ((Ident *) node)->indirection == NIL)
{
char *name = ((Ident *) node)->name;
if (clause == GROUP_CLAUSE)
{
/*
* In GROUP BY, we must prefer a match against a FROM-clause
* column to one against the targetlist. Look to see if there
* is a matching column. If so, fall through to let
* transformExpr() do the rest. NOTE: if name could refer
* ambiguously to more than one column name exposed by FROM,
* colnameToVar will elog(ERROR). That's just what we want
* here.
*/
if (colnameToVar(pstate, name) != NULL)
name = NULL;
}
if (name != NULL)
{
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
Resdom *resnode = tle->resdom;
if (!resnode->resjunk &&
strcmp(resnode->resname, name) == 0)
{
if (target_result != NULL)
{
if (!equal(target_result->expr, tle->expr))
elog(ERROR, "%s '%s' is ambiguous",
clauseText[clause], name);
}
else
target_result = tle;
/* Stay in loop to check for ambiguity */
}
}
if (target_result != NULL)
return target_result; /* return the first match */
}
}
if (IsA(node, A_Const))
{
Value *val = &((A_Const *) node)->val;
int targetlist_pos = 0;
int target_pos;
if (!IsA(val, Integer))
elog(ERROR, "Non-integer constant in %s", clauseText[clause]);
target_pos = intVal(val);
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
Resdom *resnode = tle->resdom;
if (!resnode->resjunk)
{
if (++targetlist_pos == target_pos)
return tle; /* return the unique match */
}
}
elog(ERROR, "%s position %d is not in target list",
clauseText[clause], target_pos);
}
/*
* Otherwise, we have an expression (this is a Postgres extension not
* found in SQL92). Convert the untransformed node to a transformed
* expression, and search for a match in the tlist. NOTE: it doesn't
* really matter whether there is more than one match. Also, we are
* willing to match a resjunk target here, though the above cases must
* ignore resjunk targets.
*/
expr = transformExpr(pstate, node, EXPR_COLUMN_FIRST);
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
if (equal(expr, tle->expr))
return tle;
}
/*
* If no matches, construct a new target entry which is appended to
* the end of the target list. This target is given resjunk = TRUE so
* that it will not be projected into the final tuple.
*/
target_result = transformTargetEntry(pstate, node, expr, NULL, true);
lappend(tlist, target_result);
return target_result;
}
/*
* transformGroupClause -
* transform a Group By clause
*
*/
List *
transformGroupClause(ParseState *pstate, List *grouplist, List *targetlist)
{
List *glist = NIL,
*gl;
foreach(gl, grouplist)
{
TargetEntry *tle;
tle = findTargetlistEntry(pstate, lfirst(gl),
targetlist, GROUP_CLAUSE);
/* avoid making duplicate grouplist entries */
if (!exprIsInSortList(tle->expr, glist, targetlist))
{
GroupClause *grpcl = makeNode(GroupClause);
grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
grpcl->sortop = any_ordering_op(tle->resdom->restype);
glist = lappend(glist, grpcl);
}
}
return glist;
}
/*
* transformSortClause -
* transform an ORDER BY clause
*/
List *
transformSortClause(ParseState *pstate,
List *orderlist,
List *targetlist)
{
List *sortlist = NIL;
List *olitem;
foreach(olitem, orderlist)
{
SortGroupBy *sortby = lfirst(olitem);
TargetEntry *tle;
tle = findTargetlistEntry(pstate, sortby->node,
targetlist, ORDER_CLAUSE);
sortlist = addTargetToSortList(tle, sortlist, targetlist,
sortby->useOp);
}
return sortlist;
}
/*
* transformDistinctClause -
* transform a DISTINCT or DISTINCT ON clause
*
* Since we may need to add items to the query's sortClause list, that list
* is passed by reference. We might also need to add items to the query's
* targetlist, but we assume that cannot be empty initially, so we can
* lappend to it even though the pointer is passed by value.
*/
List *
transformDistinctClause(ParseState *pstate, List *distinctlist,
List *targetlist, List **sortClause)
{
List *result = NIL;
List *slitem;
List *dlitem;
/* No work if there was no DISTINCT clause */
if (distinctlist == NIL)
return NIL;
if (lfirst(distinctlist) == NIL)
{
/* We had SELECT DISTINCT */
/*
* All non-resjunk elements from target list that are not already
* in the sort list should be added to it. (We don't really care
* what order the DISTINCT fields are checked in, so we can leave
* the user's ORDER BY spec alone, and just add additional sort
* keys to it to ensure that all targetlist items get sorted.)
*/
*sortClause = addAllTargetsToSortList(*sortClause, targetlist);
/*
* Now, DISTINCT list consists of all non-resjunk sortlist items.
* Actually, all the sortlist items had better be non-resjunk!
* Otherwise, user wrote SELECT DISTINCT with an ORDER BY item
* that does not appear anywhere in the SELECT targetlist, and we
* can't implement that with only one sorting pass...
*/
foreach(slitem, *sortClause)
{
SortClause *scl = (SortClause *) lfirst(slitem);
TargetEntry *tle = get_sortgroupclause_tle(scl, targetlist);
if (tle->resdom->resjunk)
elog(ERROR, "For SELECT DISTINCT, ORDER BY expressions must appear in target list");
else
result = lappend(result, copyObject(scl));
}
}
else
{
/* We had SELECT DISTINCT ON (expr, ...) */
/*
* If the user writes both DISTINCT ON and ORDER BY, then the two
* expression lists must match (until one or the other runs out).
* Otherwise the ORDER BY requires a different sort order than the
* DISTINCT does, and we can't implement that with only one sort
* pass (and if we do two passes, the results will be rather
* unpredictable). However, it's OK to have more DISTINCT ON
* expressions than ORDER BY expressions; we can just add the
* extra DISTINCT values to the sort list, much as we did above
* for ordinary DISTINCT fields.
*
* Actually, it'd be OK for the common prefixes of the two lists to
* match in any order, but implementing that check seems like more
* trouble than it's worth.
*/
List *nextsortlist = *sortClause;
foreach(dlitem, distinctlist)
{
TargetEntry *tle;
tle = findTargetlistEntry(pstate, lfirst(dlitem),
targetlist, DISTINCT_ON_CLAUSE);
if (nextsortlist != NIL)
{
SortClause *scl = (SortClause *) lfirst(nextsortlist);
if (tle->resdom->ressortgroupref != scl->tleSortGroupRef)
elog(ERROR, "SELECT DISTINCT ON expressions must match initial ORDER BY expressions");
result = lappend(result, copyObject(scl));
nextsortlist = lnext(nextsortlist);
}
else
{
*sortClause = addTargetToSortList(tle, *sortClause,
targetlist, NULL);
/*
* Probably, the tle should always have been added at the
* end of the sort list ... but search to be safe.
*/
foreach(slitem, *sortClause)
{
SortClause *scl = (SortClause *) lfirst(slitem);
if (tle->resdom->ressortgroupref == scl->tleSortGroupRef)
{
result = lappend(result, copyObject(scl));
break;
}
}
if (slitem == NIL)
elog(ERROR, "transformDistinctClause: failed to add DISTINCT ON clause to target list");
}
}
}
return result;
}
/*
* addAllTargetsToSortList
* Make sure all non-resjunk targets in the targetlist are in the
* ORDER BY list, adding the not-yet-sorted ones to the end of the list.
* This is typically used to help implement SELECT DISTINCT.
*
* Returns the updated ORDER BY list.
*/
List *
addAllTargetsToSortList(List *sortlist, List *targetlist)
{
List *i;
foreach(i, targetlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(i);
if (!tle->resdom->resjunk)
sortlist = addTargetToSortList(tle, sortlist, targetlist, NULL);
}
return sortlist;
}
/*
* addTargetToSortList
* If the given targetlist entry isn't already in the ORDER BY list,
* add it to the end of the list, using the sortop with given name
* or any available sort operator if opname == NULL.
*
* Returns the updated ORDER BY list.
*/
static List *
addTargetToSortList(TargetEntry *tle, List *sortlist, List *targetlist,
char *opname)
{
/* avoid making duplicate sortlist entries */
if (!exprIsInSortList(tle->expr, sortlist, targetlist))
{
SortClause *sortcl = makeNode(SortClause);
sortcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
if (opname)
sortcl->sortop = compatible_oper_opid(opname,
tle->resdom->restype,
tle->resdom->restype,
false);
else
sortcl->sortop = any_ordering_op(tle->resdom->restype);
sortlist = lappend(sortlist, sortcl);
}
return sortlist;
}
/*
* assignSortGroupRef
* Assign the targetentry an unused ressortgroupref, if it doesn't
* already have one. Return the assigned or pre-existing refnumber.
*
* 'tlist' is the targetlist containing (or to contain) the given targetentry.
*/
Index
assignSortGroupRef(TargetEntry *tle, List *tlist)
{
Index maxRef;
List *l;
if (tle->resdom->ressortgroupref) /* already has one? */
return tle->resdom->ressortgroupref;
/* easiest way to pick an unused refnumber: max used + 1 */
maxRef = 0;
foreach(l, tlist)
{
Index ref = ((TargetEntry *) lfirst(l))->resdom->ressortgroupref;
if (ref > maxRef)
maxRef = ref;
}
tle->resdom->ressortgroupref = maxRef + 1;
return tle->resdom->ressortgroupref;
}
/*
* exprIsInSortList
* Is the given expression already in the sortlist?
* Note we will say 'yes' if it is equal() to any sortlist item,
* even though that might be a different targetlist member.
*
* Works for both SortClause and GroupClause lists.
*/
static bool
exprIsInSortList(Node *expr, List *sortList, List *targetList)
{
List *i;
foreach(i, sortList)
{
SortClause *scl = (SortClause *) lfirst(i);
if (equal(expr, get_sortgroupclause_expr(scl, targetList)))
return true;
}
return false;
}