From d48428e99aa7435ff72e2df7da05f35363e90ec3 Mon Sep 17 00:00:00 2001
From: Rucha Deodhar <rucha.deodhar@mariadb.com>
Date: Mon, 1 Aug 2022 19:39:09 +0530
Subject: [PATCH] MDEV-27151: JSON_VALUE() does not parse NULL properties
 properly

Analysis: JSON_VALUE() returns "null" string instead of NULL pointer.
Fix: When the type is JSON_VALUE_NULL (which is also a scalar) set
null_value to true and return 0 instead of returning string.
---
 mysql-test/main/func_json.result | 27 +++++++++++++++++++++++++++
 mysql-test/main/func_json.test   | 19 +++++++++++++++++++
 sql/item_jsonfunc.cc             |  7 ++++++-
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/mysql-test/main/func_json.result b/mysql-test/main/func_json.result
index 8e3b47e322a00..2c3cb2f1e7257 100644
--- a/mysql-test/main/func_json.result
+++ b/mysql-test/main/func_json.result
@@ -1016,5 +1016,32 @@ j
 {"ID": "4", "Name": "Betty", "Age": 19}
 drop table t1;
 #
+# MDEV-27151: JSON_VALUE() does not parse NULL properties properly
+#
+#
+# It is correct for JSON_EXTRACT() to give null instead of "NULL" because
+# it returns the json literal that is put inside json.
+# Hence it should return null as in 'null' string and not SQL NULL.
+# JSON_VALUE() returns the "VALUE" so it is correct for it to return SQl NULL
+#
+SELECT NULL;
+NULL
+NULL
+SELECT JSON_VALUE('{"nulltest": null}', '$.nulltest');
+JSON_VALUE('{"nulltest": null}', '$.nulltest')
+NULL
+SELECT 1 + NULL;
+1 + NULL
+NULL
+SELECT 1 + JSON_VALUE('{"nulltest": null}', '$.nulltest');
+1 + JSON_VALUE('{"nulltest": null}', '$.nulltest')
+NULL
+SELECT NULL;
+NULL
+NULL
+SELECT JSON_EXTRACT('{"a":null, "b":10, "c":"null"}', '$.a');
+JSON_EXTRACT('{"a":null, "b":10, "c":"null"}', '$.a')
+null
+#
 # End of 10.3 tests
 #
diff --git a/mysql-test/main/func_json.test b/mysql-test/main/func_json.test
index 16f323a9a56c5..51961c0406aa5 100644
--- a/mysql-test/main/func_json.test
+++ b/mysql-test/main/func_json.test
@@ -627,6 +627,25 @@ SELECT * FROM t1 WHERE JSON_EXTRACT(j, '$.Age')=19;
 
 drop table t1;
 
+--echo #
+--echo # MDEV-27151: JSON_VALUE() does not parse NULL properties properly
+--echo #
+--echo #
+--echo # It is correct for JSON_EXTRACT() to give null instead of "NULL" because
+--echo # it returns the json literal that is put inside json.
+--echo # Hence it should return null as in 'null' string and not SQL NULL.
+--echo # JSON_VALUE() returns the "VALUE" so it is correct for it to return SQl NULL
+--echo #
+
+SELECT NULL;
+SELECT JSON_VALUE('{"nulltest": null}', '$.nulltest');
+SELECT 1 + NULL;
+SELECT 1 + JSON_VALUE('{"nulltest": null}', '$.nulltest');
+
+
+SELECT NULL;
+SELECT JSON_EXTRACT('{"a":null, "b":10, "c":"null"}', '$.a');
+
 --echo #
 --echo # End of 10.3 tests
 --echo #
diff --git a/sql/item_jsonfunc.cc b/sql/item_jsonfunc.cc
index 011cfdc8fd0d7..abbff8c3e9243 100644
--- a/sql/item_jsonfunc.cc
+++ b/sql/item_jsonfunc.cc
@@ -619,6 +619,12 @@ String *Item_func_json_value::val_str(String *str)
   if (json_read_value(&je))
     goto err_return;
 
+  if (je.value_type == JSON_VALUE_NULL)
+  {
+    null_value= 1;
+    return NULL;
+  }
+
   if (unlikely(check_and_get_value(&je, str, &error)))
   {
     if (error)
@@ -1111,7 +1117,6 @@ my_decimal *Item_func_json_extract::val_decimal(my_decimal *to)
       case JSON_VALUE_OBJECT:
       case JSON_VALUE_ARRAY:
       case JSON_VALUE_FALSE:
-      // TODO: fix: NULL should be NULL
       case JSON_VALUE_NULL:
         int2my_decimal(E_DEC_FATAL_ERROR, 0, false/*unsigned_flag*/, to);
         return to;