Fix deparsing FETCH FIRST <expr> ROWS WITH TIES

In the grammar, <expr> is a c_expr, which accepts only a limited set
of simple constants and 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

1 files changed, 10 insertions, 0 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index de586d8da3c..660bf69a023 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -5300,9 +5300,19 @@ 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, ')');
 			appendStringInfo(buf, " ROWS WITH TIES");
 		}
 		else