From ae6ae424b502afcc514a2ce14de476a9714b6a75 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 12 Jun 2015 11:54:03 -0400
Subject: [PATCH] Improve error message and hint for ALTER COLUMN TYPE
can't-cast failure.
We already tried to improve this once, but the "improved" text was rather
off-target if you had provided a USING clause. Also, it seems helpful
to provide the exact text of a suggested USING clause, so users can just
copy-and-paste it when needed. Per complaint from Keith Rarick and a
suggestion from Merlin Moncure.
Back-patch to 9.2 where the current wording was adopted.
---
src/backend/commands/tablecmds.c | 25 ++++++++++++++++++-----
src/test/regress/expected/alter_table.out | 7 +++++--
src/test/regress/sql/alter_table.sql | 1 +
3 files changed, 26 insertions(+), 7 deletions(-)
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index d3833d7570f..2900f47fb72 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -7266,11 +7266,26 @@ ATPrepAlterColumnType(List **wqueue,
COERCE_IMPLICIT_CAST,
-1);
if (transform == NULL)
- ereport(ERROR,
- (errcode(ERRCODE_DATATYPE_MISMATCH),
- errmsg("column \"%s\" cannot be cast automatically to type %s",
- colName, format_type_be(targettype)),
- errhint("Specify a USING expression to perform the conversion.")));
+ {
+ /* error text depends on whether USING was specified or not */
+ if (def->raw_default != NULL)
+ ereport(ERROR,
+ (errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("result of USING clause for column \"%s\""
+ " cannot be cast automatically to type %s",
+ colName, format_type_be(targettype)),
+ errhint("You might need to add an explicit cast.")));
+ else
+ ereport(ERROR,
+ (errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("column \"%s\" cannot be cast automatically to type %s",
+ colName, format_type_be(targettype)),
+ /* translator: USING is SQL, don't translate it */
+ errhint("You might need to specify \"USING %s::%s\".",
+ quote_identifier(colName),
+ format_type_with_typemod(targettype,
+ targettypmod))));
+ }
/* Fix collations after all else */
assign_expr_collations(pstate, transform);
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index 812020357c1..edf72a74e6e 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -1689,7 +1689,7 @@ select f3,max(f1) from foo group by f3;
-- Simple tests for alter table column type
alter table foo alter f1 TYPE integer; -- fails
ERROR: column "f1" cannot be cast automatically to type integer
-HINT: Specify a USING expression to perform the conversion.
+HINT: You might need to specify "USING f1::integer".
alter table foo alter f1 TYPE varchar(10);
create table anothertab (atcol1 serial8, atcol2 boolean,
constraint anothertab_chk check (atcol1 <= 3));
@@ -1705,7 +1705,10 @@ select * from anothertab;
alter table anothertab alter column atcol1 type boolean; -- fails
ERROR: column "atcol1" cannot be cast automatically to type boolean
-HINT: Specify a USING expression to perform the conversion.
+HINT: You might need to specify "USING atcol1::boolean".
+alter table anothertab alter column atcol1 type boolean using atcol1::int; -- fails
+ERROR: result of USING clause for column "atcol1" cannot be cast automatically to type boolean
+HINT: You might need to add an explicit cast.
alter table anothertab alter column atcol1 type integer;
select * from anothertab;
atcol1 | atcol2
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 15d339a5f01..55744bfa3d6 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -1174,6 +1174,7 @@ insert into anothertab (atcol1, atcol2) values (default, false);
select * from anothertab;
alter table anothertab alter column atcol1 type boolean; -- fails
+alter table anothertab alter column atcol1 type boolean using atcol1::int; -- fails
alter table anothertab alter column atcol1 type integer;
select * from anothertab;
--
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