v2-0002-SQL-JSON-Fix-default-ON-ERROR-behavior-for-JSON_T.patch

From 5b891dac2b2781296ab9971a17f8ec0c586ebb1e Mon Sep 17 00:00:00 2001
From: Amit Langote <amitlan@postgresql.org>
Date: Fri, 30 Aug 2024 12:19:50 +0900
Subject: [PATCH v2 2/4] SQL/JSON: Fix default ON ERROR behavior for JSON_TABLE

Use EMPTY ARRAY instead of EMPTY.

This change does not affect the runtime behavior of JSON_TABLE(),
which continues to return an empty relation ON ERROR. It only alters
whether the default ON ERROR behavior is shown in the deparsed output.

Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
---
 src/backend/parser/parse_expr.c               |  4 +--
 src/backend/utils/adt/ruleutils.c             |  2 +-
 .../regress/expected/sqljson_jsontable.out    | 33 +++++++++++++++++++
 src/test/regress/sql/sqljson_jsontable.sql    |  6 ++++
 4 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 56e413da9f..36c1b7a88f 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -4603,13 +4603,13 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
 			}
 
 			/*
-			 * Assume EMPTY ON ERROR when ON ERROR is not specified.
+			 * Assume EMPTY ARRAY ON ERROR when ON ERROR is not specified.
 			 *
 			 * ON EMPTY cannot be specified at the top level but it can be for
 			 * the individual columns.
 			 */
 			jsexpr->on_error = transformJsonBehavior(pstate, func->on_error,
-													 JSON_BEHAVIOR_EMPTY,
+													 JSON_BEHAVIOR_EMPTY_ARRAY,
 													 jsexpr->returning);
 			break;
 
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index b31be31321..0aa090be20 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -11875,7 +11875,7 @@ get_json_table(TableFunc *tf, deparse_context *context, bool showimplicit)
 	get_json_table_columns(tf, castNode(JsonTablePathScan, tf->plan), context,
 						   showimplicit);
 
-	if (jexpr->on_error->btype != JSON_BEHAVIOR_EMPTY)
+	if (jexpr->on_error->btype != JSON_BEHAVIOR_EMPTY_ARRAY)
 		get_json_behavior(jexpr->on_error, context, "ERROR");
 
 	if (PRETTY_INDENT(context))
diff --git a/src/test/regress/expected/sqljson_jsontable.out b/src/test/regress/expected/sqljson_jsontable.out
index 721e01d6ad..f25d03bc77 100644
--- a/src/test/regress/expected/sqljson_jsontable.out
+++ b/src/test/regress/expected/sqljson_jsontable.out
@@ -1132,3 +1132,36 @@ ERROR:  invalid ON ERROR behavior for column "a"
 LINE 1: ...M JSON_TABLE(jsonb '1', '$' COLUMNS (a int exists empty obje...
                                                              ^
 DETAIL:  Only ERROR, TRUE, FALSE, or UNKNOWN is allowed in ON ERROR for EXISTS columns.
+-- Test JSON_TABLE() deparsing -- don't emit default ON ERROR behavior
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$'));
+                                             QUERY PLAN                                              
+-----------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS json_table_path_0 COLUMNS (a text PATH '$'))
+(3 rows)
+
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') EMPTY ON ERROR);
+                                             QUERY PLAN                                              
+-----------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS json_table_path_0 COLUMNS (a text PATH '$'))
+(3 rows)
+
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') EMPTY ARRAY ON ERROR);
+                                             QUERY PLAN                                              
+-----------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS json_table_path_0 COLUMNS (a text PATH '$'))
+(3 rows)
+
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') ERROR ON ERROR);
+                                                                   QUERY PLAN                                                                   
+------------------------------------------------------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS json_table_path_0 COLUMNS (a text PATH '$' NULL ON EMPTY NULL ON ERROR) ERROR ON ERROR)
+(3 rows)
+
diff --git a/src/test/regress/sql/sqljson_jsontable.sql b/src/test/regress/sql/sqljson_jsontable.sql
index 38992316f5..932a3ecf59 100644
--- a/src/test/regress/sql/sqljson_jsontable.sql
+++ b/src/test/regress/sql/sqljson_jsontable.sql
@@ -542,3 +542,9 @@ SELECT * FROM JSON_TABLE(jsonb '1', '$' COLUMNS (a int) NULL ON ERROR);
 SELECT * FROM JSON_TABLE(jsonb '1', '$' COLUMNS (a int true on empty));
 SELECT * FROM JSON_TABLE(jsonb '1', '$' COLUMNS (a int omit quotes true on error));
 SELECT * FROM JSON_TABLE(jsonb '1', '$' COLUMNS (a int exists empty object on error));
+
+-- Test JSON_TABLE() deparsing -- don't emit default ON ERROR behavior
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$'));
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') EMPTY ON ERROR);
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') EMPTY ARRAY ON ERROR);
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') ERROR ON ERROR);
-- 
2.43.0