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Commit5c056b0

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Don't elide casting to typmod -1.
Casting a value that's already of a type with a specific typmodto an unspecified typmod doesn't do anything so far as run-timebehavior is concerned. However, it really ought to change theexposed type of the expression to match. Up to now,coerce_type_typmod hasn't bothered with that, which creates gotchasin contexts such as recursive unions. If for example one side ofthe union is numeric(18,3), but it needs to be plain numeric tomatch the other side, there's no direct way to express that.This is easy enough to fix, by inserting a RelabelType to update theexposed type of the expression. However, it's a bit nervous-makingto change this behavior, because it's stood for a really long time.(I strongly suspect that it's like this in part because the logicpre-dates the introduction of RelabelType in 7.0. The commit logmessage for57b30e8 is interesting reading here.) As a compromise,we'll sneak the change into 14beta3, and consider back-patching tostable branches if no complaints emerge in the next three months.Discussion:https://postgr.es/m/CABNQVagu3bZGqiTjb31a8D5Od3fUMs7Oh3gmZMQZVHZ=uWWWfQ@mail.gmail.com
1 parent2642df9 commit5c056b0

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3 files changed

+75
-9
lines changed

3 files changed

+75
-9
lines changed

‎src/backend/parser/parse_coerce.c

Lines changed: 17 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -758,25 +758,33 @@ coerce_type_typmod(Node *node, Oid targetTypeId, int32 targetTypMod,
758758
CoercionPathTypepathtype;
759759
OidfuncId;
760760

761-
/*
762-
* A negative typmod is assumed to mean that no coercion is wanted. Also,
763-
* skip coercion if already done.
764-
*/
765-
if (targetTypMod<0||targetTypMod==exprTypmod(node))
761+
/* Skip coercion if already done */
762+
if (targetTypMod==exprTypmod(node))
766763
returnnode;
767764

765+
/* Suppress display of nested coercion steps */
766+
if (hideInputCoercion)
767+
hide_coercion_node(node);
768+
768769
pathtype=find_typmod_coercion_function(targetTypeId,&funcId);
769770

770771
if (pathtype!=COERCION_PATH_NONE)
771772
{
772-
/* Suppress display of nested coercion steps */
773-
if (hideInputCoercion)
774-
hide_coercion_node(node);
775-
776773
node=build_coercion_expression(node,pathtype,funcId,
777774
targetTypeId,targetTypMod,
778775
ccontext,cformat,location);
779776
}
777+
else
778+
{
779+
/*
780+
* We don't need to perform any actual coercion step, but we should
781+
* apply a RelabelType to ensure that the expression exposes the
782+
* intended typmod.
783+
*/
784+
node=applyRelabelType(node,targetTypeId,targetTypMod,
785+
exprCollation(node),
786+
cformat,location, false);
787+
}
780788

781789
returnnode;
782790
}

‎src/test/regress/expected/expressions.out

Lines changed: 37 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -158,6 +158,43 @@ select count(*) from date_tbl
158158
13
159159
(1 row)
160160

161+
--
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-- Test parsing of a no-op cast to a type with unspecified typmod
163+
--
164+
begin;
165+
create table numeric_tbl (f1 numeric(18,3), f2 numeric);
166+
create view numeric_view as
167+
select
168+
f1, f1::numeric(16,4) as f1164, f1::numeric as f1n,
169+
f2, f2::numeric(16,4) as f2164, f2::numeric as f2n
170+
from numeric_tbl;
171+
\d+ numeric_view
172+
View "public.numeric_view"
173+
Column | Type | Collation | Nullable | Default | Storage | Description
174+
--------+---------------+-----------+----------+---------+---------+-------------
175+
f1 | numeric(18,3) | | | | main |
176+
f1164 | numeric(16,4) | | | | main |
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f1n | numeric | | | | main |
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f2 | numeric | | | | main |
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f2164 | numeric(16,4) | | | | main |
180+
f2n | numeric | | | | main |
181+
View definition:
182+
SELECT numeric_tbl.f1,
183+
numeric_tbl.f1::numeric(16,4) AS f1164,
184+
numeric_tbl.f1::numeric AS f1n,
185+
numeric_tbl.f2,
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numeric_tbl.f2::numeric(16,4) AS f2164,
187+
numeric_tbl.f2 AS f2n
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FROM numeric_tbl;
189+
190+
explain (verbose, costs off) select * from numeric_view;
191+
QUERY PLAN
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-------------------------------------------------------------------------------------------------------------------------------------------------------
193+
Seq Scan on public.numeric_tbl
194+
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
195+
(2 rows)
196+
197+
rollback;
161198
--
162199
-- Tests for ScalarArrayOpExpr with a hashfn
163200
--

‎src/test/regress/sql/expressions.sql

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -66,6 +66,27 @@ select count(*) from date_tbl
6666
selectcount(*)from date_tbl
6767
where f1 not between symmetric'1997-01-01'and'1998-01-01';
6868

69+
70+
--
71+
-- Test parsing of a no-op cast to a type with unspecified typmod
72+
--
73+
begin;
74+
75+
createtablenumeric_tbl (f1numeric(18,3), f2numeric);
76+
77+
createviewnumeric_viewas
78+
select
79+
f1, f1::numeric(16,4)as f1164, f1::numericas f1n,
80+
f2, f2::numeric(16,4)as f2164, f2::numericas f2n
81+
from numeric_tbl;
82+
83+
\d+ numeric_view
84+
85+
explain (verbose, costs off)select*from numeric_view;
86+
87+
rollback;
88+
89+
6990
--
7091
-- Tests for ScalarArrayOpExpr with a hashfn
7192
--

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