SQL/JSON: Fix JSON_TABLE() column deparsing

The deparsing code in get_json_expr_options() unnecessarily emitted
the default column-specific ON ERROR / EMPTY behavior when the
top-level ON ERROR behavior in JSON_TABLE was set to ERROR. Fix that
by not overriding the column-specific default, determined based on
the column's JsonExprOp in get_json_table_columns(), with
JSON_BEHAVIOR_ERROR when that is the top-level ON ERROR behavior.

Note that this only removes redundancy; the current deparsing output
is not incorrect, just redundant.

Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

Author: amitlan

src/backend/utils/adt/ruleutils.c

@@ -11719,7 +11719,6 @@ get_json_table_columns(TableFunc *tf, JsonTablePathScan *scan,
 					   bool showimplicit)
 {
 	StringInfo	buf = context->buf;
-	JsonExpr   *jexpr = castNode(JsonExpr, tf->docexpr);
 	ListCell   *lc_colname;
 	ListCell   *lc_coltype;
 	ListCell   *lc_coltypmod;
@@ -11772,6 +11771,10 @@ get_json_table_columns(TableFunc *tf, JsonTablePathScan *scan,
 		if (ordinality)
 			continue;
 
+		/*
+		 * Set default_behavior to guide get_json_expr_options() on whether to
+		 * to emit the ON ERROR / EMPTY clauses.
+		 */
 		if (colexpr->op == JSON_EXISTS_OP)
 		{
 			appendStringInfoString(buf, " EXISTS");
@@ -11795,9 +11798,6 @@ get_json_table_columns(TableFunc *tf, JsonTablePathScan *scan,
 			default_behavior = JSON_BEHAVIOR_NULL;
 		}
 
-		if (jexpr->on_error->btype == JSON_BEHAVIOR_ERROR)
-			default_behavior = JSON_BEHAVIOR_ERROR;
-
 		appendStringInfoString(buf, " PATH ");
 
 		get_json_path_spec(colexpr->path_spec, context, showimplicit);

src/test/regress/expected/sqljson_jsontable.out

@@ -1132,3 +1132,21 @@ ERROR:  invalid ON ERROR behavior for column "a"
 LINE 1: ...M JSON_TABLE(jsonb '1', '$' COLUMNS (a int exists empty obje...
                                                              ^
 DETAIL:  Only ERROR, TRUE, FALSE, or UNKNOWN is allowed in ON ERROR for EXISTS columns.
+-- Test JSON_TABLE() column deparsing -- don't emit default ON ERROR / EMPTY
+-- behavior
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' 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 '$') ERROR ON ERROR);
+                                                     QUERY PLAN                                                     
+--------------------------------------------------------------------------------------------------------------------
+ Table Function Scan on "json_table"  (cost=0.01..1.00 rows=100 width=32)
+   Output: a
+   Table Function Call: JSON_TABLE('"a"'::jsonb, '$' AS json_table_path_0 COLUMNS (a text PATH '$') ERROR ON ERROR)
+(3 rows)
+

src/test/regress/sql/sqljson_jsontable.sql

@@ -542,3 +542,8 @@ 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() column deparsing -- don't emit default ON ERROR / EMPTY
+-- behavior
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$'));
+EXPLAIN VERBOSE SELECT * from JSON_TABLE('"a"', '$' COLUMNS (a text PATH '$') ERROR ON ERROR);