Fix deparsing FETCH FIRST <expr> ROWS WITH TIES

In the grammar, <expr> is a c_expr, which accepts only a limited set
of integer literals and simple expressions without parens. The
deparsing logic didn't quite match the grammar rule, and failed to use
parens e.g. for "5::bigint".

To fix, always surround the expression with parens. Would be nice to
omit the parens in simple cases, but unfortunately it's non-trivial to
detect such simple cases. Even if the expression is a simple literal
123 in the original query, after parse analysis it becomes a FuncExpr
with COERCE_IMPLICIT_CAST rather than a simple Const.

Reported-by: yonghao lee
Backpatch-through: 13
Discussion: https://www.postgresql.org/message-id/18929-077d6b7093b176e2@postgresql.org

3 files changed, 31 insertions, 4 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 467b08198b8..3d6e6bdbfd2 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -5956,9 +5956,19 @@ get_select_query_def(Query *query, deparse_context *context)
 	{
 		if (query->limitOption == LIMIT_OPTION_WITH_TIES)
 		{
+			/*
+			 * The limitCount arg is a c_expr, so it needs parens. Simple
+			 * literals and function expressions would not need parens, but
+			 * unfortunately it's hard to tell if the expression will be
+			 * printed as a simple literal like 123 or as a typecast
+			 * expression, like '-123'::int4. The grammar accepts the former
+			 * without quoting, but not the latter.
+			 */
 			appendContextKeyword(context, " FETCH FIRST ",
 								 -PRETTYINDENT_STD, PRETTYINDENT_STD, 0);
+			appendStringInfoChar(buf, '(');
 			get_rule_expr(query->limitCount, context, false);
+			appendStringInfoChar(buf, ')');
 			appendStringInfoString(buf, " ROWS WITH TIES");
 		}
 		else
diff --git a/src/test/regress/expected/limit.out b/src/test/regress/expected/limit.out
index f4267c002d7..e3bcc680653 100644
--- a/src/test/regress/expected/limit.out
+++ b/src/test/regress/expected/limit.out
@@ -647,7 +647,7 @@ View definition:
   WHERE thousand < 995
   ORDER BY thousand
  OFFSET 10
- FETCH FIRST 5 ROWS WITH TIES;
+ FETCH FIRST (5) ROWS WITH TIES;
 
 CREATE VIEW limit_thousand_v_2 AS SELECT thousand FROM onek WHERE thousand < 995
 		ORDER BY thousand OFFSET 10 FETCH FIRST 5 ROWS ONLY;
@@ -679,10 +679,10 @@ View definition:
    FROM onek
   WHERE thousand < 995
   ORDER BY thousand
- FETCH FIRST (NULL::integer + 1) ROWS WITH TIES;
+ FETCH FIRST ((NULL::integer + 1)) ROWS WITH TIES;
 
 CREATE VIEW limit_thousand_v_4 AS SELECT thousand FROM onek WHERE thousand < 995
-		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+		ORDER BY thousand FETCH FIRST (5::bigint) ROWS WITH TIES;
 \d+ limit_thousand_v_4
                       View "public.limit_thousand_v_4"
   Column  |  Type   | Collation | Nullable | Default | Storage | Description 
@@ -693,6 +693,20 @@ View definition:
    FROM onek
   WHERE thousand < 995
   ORDER BY thousand
+ FETCH FIRST (5::bigint) ROWS WITH TIES;
+
+CREATE VIEW limit_thousand_v_5 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+\d+ limit_thousand_v_5
+                      View "public.limit_thousand_v_5"
+  Column  |  Type   | Collation | Nullable | Default | Storage | Description 
+----------+---------+-----------+----------+---------+---------+-------------
+ thousand | integer |           |          |         | plain   | 
+View definition:
+ SELECT thousand
+   FROM onek
+  WHERE thousand < 995
+  ORDER BY thousand
  LIMIT ALL;
 
 -- leave these views
diff --git a/src/test/regress/sql/limit.sql b/src/test/regress/sql/limit.sql
index 6f0cda98701..603910fe6d1 100644
--- a/src/test/regress/sql/limit.sql
+++ b/src/test/regress/sql/limit.sql
@@ -196,6 +196,9 @@ CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
 		ORDER BY thousand FETCH FIRST (NULL+1) ROWS WITH TIES;
 \d+ limit_thousand_v_3
 CREATE VIEW limit_thousand_v_4 AS SELECT thousand FROM onek WHERE thousand < 995
-		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+		ORDER BY thousand FETCH FIRST (5::bigint) ROWS WITH TIES;
 \d+ limit_thousand_v_4
+CREATE VIEW limit_thousand_v_5 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+\d+ limit_thousand_v_5
 -- leave these views