From fadb48b00e02ccfd152baa80942de30205ab3c4f Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <andrew@dunslane.net>
Date: Tue, 5 Apr 2022 14:09:04 -0400
Subject: PLAN clauses for JSON_TABLE

These clauses allow the user to specify how data from nested paths are
joined, allowing considerable freedom in shaping the tabular output of
JSON_TABLE.

PLAN DEFAULT allows the user to specify the global strategies when
dealing with sibling or child nested paths. The is often sufficient to
achieve the necessary goal, and is considerably simpler than the full
PLAN clause, which allows the user to specify the strategy to be used
for each named nested path.

Nikita Glukhov

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zhihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/7e2cb85d-24cf-4abb-30a5-1a33715959bd@postgrespro.ru
---
 src/backend/utils/adt/ruleutils.c | 50 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

(limited to 'src/backend/utils/adt/ruleutils.c')

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index e6173a9db42..3296ad070ed 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -11169,10 +11169,54 @@ get_json_table_nested_columns(TableFunc *tf, Node *node,
 		 appendStringInfoChar(context->buf, ' ');
 		 appendContextKeyword(context,  "NESTED PATH ", 0, 0, 0);
 		 get_const_expr(n->path, context, -1);
+		 appendStringInfo(context->buf, " AS %s", quote_identifier(n->name));
 		 get_json_table_columns(tf, n, context, showimplicit);
 	}
 }
 
+/*
+ * get_json_table_plan - Parse back a JSON_TABLE plan
+ */
+static void
+get_json_table_plan(TableFunc *tf, Node *node, deparse_context *context,
+					bool parenthesize)
+{
+	if (parenthesize)
+		appendStringInfoChar(context->buf, '(');
+
+	if (IsA(node, JsonTableSibling))
+	{
+		JsonTableSibling *n = (JsonTableSibling *) node;
+
+		get_json_table_plan(tf, n->larg, context,
+							IsA(n->larg, JsonTableSibling) ||
+							castNode(JsonTableParent, n->larg)->child);
+
+		appendStringInfoString(context->buf, n->cross ? " CROSS " : " UNION ");
+
+		get_json_table_plan(tf, n->rarg, context,
+							IsA(n->rarg, JsonTableSibling) ||
+							castNode(JsonTableParent, n->rarg)->child);
+	}
+	else
+	{
+		 JsonTableParent *n = castNode(JsonTableParent, node);
+
+		 appendStringInfoString(context->buf, quote_identifier(n->name));
+
+		 if (n->child)
+		 {
+			appendStringInfoString(context->buf,
+								   n->outerJoin ? " OUTER " : " INNER ");
+			get_json_table_plan(tf, n->child, context,
+								IsA(n->child, JsonTableSibling));
+		 }
+	}
+
+	if (parenthesize)
+		appendStringInfoChar(context->buf, ')');
+}
+
 /*
  * get_json_table_columns - Parse back JSON_TABLE columns
  */
@@ -11301,6 +11345,8 @@ get_json_table(TableFunc *tf, deparse_context *context, bool showimplicit)
 
 	get_const_expr(root->path, context, -1);
 
+	appendStringInfo(buf, " AS %s", quote_identifier(root->name));
+
 	if (jexpr->passing_values)
 	{
 		ListCell   *lc1, *lc2;
@@ -11333,6 +11379,10 @@ get_json_table(TableFunc *tf, deparse_context *context, bool showimplicit)
 
 	get_json_table_columns(tf, root, context, showimplicit);
 
+	appendStringInfoChar(buf, ' ');
+	appendContextKeyword(context, "PLAN ", 0, 0, 0);
+	get_json_table_plan(tf, (Node *) root, context, true);
+
 	if (jexpr->on_error->btype != JSON_BEHAVIOR_EMPTY)
 		get_json_behavior(jexpr->on_error, context, "ERROR");
 
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