postgres.git / summary / log / commit / refs
commit 5c056b0c2519e602c2e98bace5b16d2ecde6454b
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri Aug 06 21:32:54 2021 +0000
First released in: 15.0, 14.0
Don't elide casting to typmod -1.
Casting a value that's already of a type with a specific typmod
to an unspecified typmod doesn't do anything so far as run-time
behavior is concerned. However, it really ought to change the
exposed type of the expression to match. Up to now,
coerce_type_typmod hasn't bothered with that, which creates gotchas
in contexts such as recursive unions. If for example one side of
the union is numeric(18,3), but it needs to be plain numeric to
match the other side, there's no direct way to express that.
This is easy enough to fix, by inserting a RelabelType to update the
exposed type of the expression. However, it's a bit nervous-making
to change this behavior, because it's stood for a really long time.
(I strongly suspect that it's like this in part because the logic
pre-dates the introduction of RelabelType in 7.0. The commit log
message for 57b30e8e2 is interesting reading here.) As a compromise,
we'll sneak the change into 14beta3, and consider back-patching to
stable branches if no complaints emerge in the next three months.
Discussion: https://postgr.es/m/CABNQVagu3bZGqiTjb31a8D5Od3fUMs7Oh3gmZMQZVHZ=uWWWfQ@mail.gmail.com
src/backend/parser/parse_coerce.c | 26 ++++++++++++++--------
src/test/regress/expected/expressions.out | 37 +++++++++++++++++++++++++++++++
src/test/regress/sql/expressions.sql | 21 ++++++++++++++++++
3 files changed, 75 insertions(+), 9 deletions(-)
diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index 5da72a4c36d..78194afedfb 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -758,25 +758,33 @@ coerce_type_typmod(Node *node, Oid targetTypeId, int32 targetTypMod,
CoercionPathType pathtype;
Oid funcId;
- /*
- * A negative typmod is assumed to mean that no coercion is wanted. Also,
- * skip coercion if already done.
- */
- if (targetTypMod < 0 || targetTypMod == exprTypmod(node))
+ /* Skip coercion if already done */
+ if (targetTypMod == exprTypmod(node))
return node;
+ /* Suppress display of nested coercion steps */
+ if (hideInputCoercion)
+ hide_coercion_node(node);
+
pathtype = find_typmod_coercion_function(targetTypeId, &funcId);
if (pathtype != COERCION_PATH_NONE)
{
- /* Suppress display of nested coercion steps */
- if (hideInputCoercion)
- hide_coercion_node(node);
-
node = build_coercion_expression(node, pathtype, funcId,
targetTypeId, targetTypMod,
ccontext, cformat, location);
}
+ else
+ {
+ /*
+ * We don't need to perform any actual coercion step, but we should
+ * apply a RelabelType to ensure that the expression exposes the
+ * intended typmod.
+ */
+ node = applyRelabelType(node, targetTypeId, targetTypMod,
+ exprCollation(node),
+ cformat, location, false);
+ }
return node;
}
diff --git a/src/test/regress/expected/expressions.out b/src/test/regress/expected/expressions.out
index 84159cb21fc..7b6b0bb4f99 100644
--- a/src/test/regress/expected/expressions.out
+++ b/src/test/regress/expected/expressions.out
@@ -158,6 +158,43 @@ select count(*) from date_tbl
13
(1 row)
+--
+-- Test parsing of a no-op cast to a type with unspecified typmod
+--
+begin;
+create table numeric_tbl (f1 numeric(18,3), f2 numeric);
+create view numeric_view as
+ select
+ f1, f1::numeric(16,4) as f1164, f1::numeric as f1n,
+ f2, f2::numeric(16,4) as f2164, f2::numeric as f2n
+ from numeric_tbl;
+\d+ numeric_view
+ View "public.numeric_view"
+ Column | Type | Collation | Nullable | Default | Storage | Description
+--------+---------------+-----------+----------+---------+---------+-------------
+ f1 | numeric(18,3) | | | | main |
+ f1164 | numeric(16,4) | | | | main |
+ f1n | numeric | | | | main |
+ f2 | numeric | | | | main |
+ f2164 | numeric(16,4) | | | | main |
+ f2n | numeric | | | | main |
+View definition:
+ SELECT numeric_tbl.f1,
+ numeric_tbl.f1::numeric(16,4) AS f1164,
+ numeric_tbl.f1::numeric AS f1n,
+ numeric_tbl.f2,
+ numeric_tbl.f2::numeric(16,4) AS f2164,
+ numeric_tbl.f2 AS f2n
+ FROM numeric_tbl;
+
+explain (verbose, costs off) select * from numeric_view;
+ QUERY PLAN
+-------------------------------------------------------------------------------------------------------------------------------------------------------
+ Seq Scan on public.numeric_tbl
+ Output: numeric_tbl.f1, (numeric_tbl.f1)::numeric(16,4), (numeric_tbl.f1)::numeric, numeric_tbl.f2, (numeric_tbl.f2)::numeric(16,4), numeric_tbl.f2
+(2 rows)
+
+rollback;
--
-- Tests for ScalarArrayOpExpr with a hashfn
--
diff --git a/src/test/regress/sql/expressions.sql b/src/test/regress/sql/expressions.sql
index bf30f415056..e9aa1a0b289 100644
--- a/src/test/regress/sql/expressions.sql
+++ b/src/test/regress/sql/expressions.sql
@@ -66,6 +66,27 @@ select count(*) from date_tbl
select count(*) from date_tbl
where f1 not between symmetric '1997-01-01' and '1998-01-01';
+
+--
+-- Test parsing of a no-op cast to a type with unspecified typmod
+--
+begin;
+
+create table numeric_tbl (f1 numeric(18,3), f2 numeric);
+
+create view numeric_view as
+ select
+ f1, f1::numeric(16,4) as f1164, f1::numeric as f1n,
+ f2, f2::numeric(16,4) as f2164, f2::numeric as f2n
+ from numeric_tbl;
+
+\d+ numeric_view
+
+explain (verbose, costs off) select * from numeric_view;
+
+rollback;
+
+
--
-- Tests for ScalarArrayOpExpr with a hashfn
--
[parent: 2642df9fac09]