From 1a36bc9dba8eae90963a586d37b6457b32b2fed4 Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <andrew@dunslane.net>
Date: Thu, 3 Mar 2022 13:11:14 -0500
Subject: SQL/JSON query functions

This introduces the SQL/JSON functions for querying JSON data using
jsonpath expressions. The functions are:

JSON_EXISTS()
JSON_QUERY()
JSON_VALUE()

All of these functions only operate on jsonb. The workaround for now is
to cast the argument to jsonb.

JSON_EXISTS() tests if the jsonpath expression applied to the jsonb
value yields any values. JSON_VALUE() must return a single value, and an
error occurs if it tries to return multiple values. JSON_QUERY() must
return a json object or array, and there are various WRAPPER options for
handling scalar or multi-value results. Both these functions have
options for handling EMPTY and ERROR conditions.

Nikita Glukhov

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

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
---
 src/backend/optimizer/path/costsize.c |  3 ++-
 src/backend/optimizer/util/clauses.c  | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

(limited to 'src/backend/optimizer')

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 1b07ea392d9..679d8ed597e 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -4547,7 +4547,8 @@ cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
 			 IsA(node, SQLValueFunction) ||
 			 IsA(node, XmlExpr) ||
 			 IsA(node, CoerceToDomain) ||
-			 IsA(node, NextValueExpr))
+			 IsA(node, NextValueExpr) ||
+			 IsA(node, JsonExpr))
 	{
 		/* Treat all these as having cost 1 */
 		context->total.per_tuple += cpu_operator_cost;
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index e1147c431e6..e381ae512a2 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -28,6 +28,7 @@
 #include "catalog/pg_type.h"
 #include "executor/executor.h"
 #include "executor/functions.h"
+#include "executor/execExpr.h"
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -52,6 +53,7 @@
 #include "utils/fmgroids.h"
 #include "utils/json.h"
 #include "utils/jsonb.h"
+#include "utils/jsonpath.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/syscache.h"
@@ -405,6 +407,24 @@ contain_mutable_functions_walker(Node *node, void *context)
 		/* Check all subnodes */
 	}
 
+	if (IsA(node, JsonExpr))
+	{
+		JsonExpr   *jexpr = castNode(JsonExpr, node);
+		Const	   *cnst;
+
+		if (!IsA(jexpr->path_spec, Const))
+			return true;
+
+		cnst = castNode(Const, jexpr->path_spec);
+
+		Assert(cnst->consttype == JSONPATHOID);
+		if (cnst->constisnull)
+			return false;
+
+		return jspIsMutable(DatumGetJsonPathP(cnst->constvalue),
+							jexpr->passing_names, jexpr->passing_values);
+	}
+
 	if (IsA(node, SQLValueFunction))
 	{
 		/* all variants of SQLValueFunction are stable */
@@ -876,6 +896,18 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context)
 								 context, 0);
 	}
 
+	/* JsonExpr is parallel-unsafe if subtransactions can be used. */
+	else if (IsA(node, JsonExpr))
+	{
+		JsonExpr  *jsexpr = (JsonExpr *) node;
+
+		if (ExecEvalJsonNeedsSubTransaction(jsexpr, NULL))
+		{
+			context->max_hazard = PROPARALLEL_UNSAFE;
+			return true;
+		}
+	}
+
 	/* Recurse to check arguments */
 	return expression_tree_walker(node,
 								  max_parallel_hazard_walker,
-- 
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