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Improve error message for ALTER COLUMN TYPE coercion failure.

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Per recent discussion, the error message for this was actually a trifle
inaccurate, since it said "cannot be cast" which might be incorrect.
Adjust that wording, and add a HINT suggesting that a USING clause might
be needed.
This commit is contained in:
Tom Lane 2012-05-15 12:12:40 -04:00
parent 6593c5b5dc
commit 488c6dd170
2 changed files with 9 additions and 6 deletions
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7
src/backend/commands/tablecmds.c
View File

@ -7315,8 +7315,9 @@ ATPrepAlterColumnType(List **wqueue,
if (transform == NULL)
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("column \"%s\" cannot be cast to type %s",
colName, format_type_be(targettype))));
errmsg("column \"%s\" cannot be cast automatically to type %s",
colName, format_type_be(targettype)),
errhint("Specify a USING expression to perform the conversion.")));
/* Fix collations after all else */
assign_expr_collations(pstate, transform);
@ -7482,7 +7483,7 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
if (defaultexpr == NULL)
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("default for column \"%s\" cannot be cast to type %s",
errmsg("default for column \"%s\" cannot be cast automatically to type %s",
colName, format_type_be(targettype))));
}
else

8
src/test/regress/expected/alter_table.out
View File

@ -1673,7 +1673,8 @@ 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 to type integer
ERROR: column "f1" cannot be cast automatically to type integer
HINT: Specify a USING expression to perform the conversion.
alter table foo alter f1 TYPE varchar(10);
create table anothertab (atcol1 serial8, atcol2 boolean,
constraint anothertab_chk check (atcol1 <= 3));
@ -1688,7 +1689,8 @@ select * from anothertab;
(2 rows)
alter table anothertab alter column atcol1 type boolean; -- fails
ERROR: column "atcol1" cannot be cast to type boolean
ERROR: column "atcol1" cannot be cast automatically to type boolean
HINT: Specify a USING expression to perform the conversion.
alter table anothertab alter column atcol1 type integer;
select * from anothertab;
atcol1 | atcol2
@ -1723,7 +1725,7 @@ select * from anothertab;
alter table anothertab alter column atcol1 type boolean
using case when atcol1 % 2 = 0 then true else false end; -- fails
ERROR: default for column "atcol1" cannot be cast to type boolean
ERROR: default for column "atcol1" cannot be cast automatically to type boolean
alter table anothertab alter column atcol1 drop default;
alter table anothertab alter column atcol1 type boolean
using case when atcol1 % 2 = 0 then true else false end; -- fails