From e5f6493e3584ea7eec1f992f87639e7f186ae03e Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 6 Aug 2021 17:32:54 -0400 Subject: [PATCH] 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 5da72a4c36..78194afedf 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 5944dfd5e1..54ef7213d1 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 b3fd1b5ecb..6836503735 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 --