[fix](function) JSON_EXTRACT_STRING should return NULL instead of the string 'null' when encountering a NULL value (#51516)

mrhhsg · Your Name · commit a8365ffecc40 · 2025-06-07T13:16:10.000Z
### What problem does this PR solve?

Previously, when JSON_EXTRACT_STRING encountered a NULL input value or
path, it returned the string "null" instead of a proper SQL NULL value.
This behavior could lead to incorrect query results and confusion in
downstream processing that expects NULL to be represented as an actual
null value rather than a literal string.

This commit adjusts the logic to ensure that JSON_EXTRACT_STRING returns
NULL in such cases, aligning with SQL semantics and improving
compatibility with systems that rely on strict null-handling behavior.
diff --git a/be/src/vec/functions/function_jsonb.cpp b/be/src/vec/functions/function_jsonb.cpp
@@ -793,7 +793,7 @@ struct JsonbExtractStringImpl {
                         std::string_view(str_value->getBlob(), str_value->length()), i, res_data,
                         res_offsets);
             } else if (value->isNull()) {
-                StringOP::push_value_string("null", i, res_data, res_offsets);
+                StringOP::push_null_string(i, res_data, res_offsets, null_map);
             } else if (value->isTrue()) {
                 StringOP::push_value_string("true", i, res_data, res_offsets);
             } else if (value->isFalse()) {
diff --git a/be/test/vec/function/function_jsonb_test.cpp b/be/test/vec/function/function_jsonb_test.cpp
@@ -667,7 +667,7 @@ TEST(FunctionJsonbTEST, JsonbExtractStringTest) {
     // json_extract root
     DataSet data_set = {
             {{Null(), STRING("$")}, Null()},
-            {{STRING("null"), STRING("$")}, STRING("null")},
+            {{STRING("null"), STRING("$")}, Null()},
             {{STRING("true"), STRING("$")}, STRING("true")},
             {{STRING("false"), STRING("$")}, STRING("false")},
             {{STRING("100"), STRING("$")}, STRING("100")},                                 //int8
@@ -751,7 +751,7 @@ TEST(FunctionJsonbTEST, JsonbExtractStringTest) {
             {{STRING(R"(["abc", "def"])"), STRING("$[1]")}, STRING("def")},   // string array
             {{STRING(R"(["abc", "def"])"), STRING("$[2]")}, Null()},          // string array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[0]")},
-             STRING("null")}, // multi type array
+             Null()}, // multi type array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[1]")},
              STRING("true")}, // multi type array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[2]")},
@@ -1521,7 +1521,7 @@ TEST(FunctionJsonbTEST, GetJSONSTRINGTest) {
     // get json from root
     DataSet data_set = {
             {{Null(), STRING("$")}, Null()},
-            {{STRING("null"), STRING("$")}, STRING("null")},
+            {{STRING("null"), STRING("$")}, Null()},
             {{STRING("true"), STRING("$")}, STRING("true")},
             {{STRING("false"), STRING("$")}, STRING("false")},
             {{STRING("100"), STRING("$")}, STRING("100")},                                 //int8
@@ -1605,7 +1605,7 @@ TEST(FunctionJsonbTEST, GetJSONSTRINGTest) {
             {{STRING(R"(["abc", "def"])"), STRING("$[1]")}, STRING("def")},   // string array
             {{STRING(R"(["abc", "def"])"), STRING("$[2]")}, Null()},          // string array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[0]")},
-             STRING("null")}, // multi type array
+             Null()}, // multi type array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[1]")},
              STRING("true")}, // multi type array
             {{STRING(R"([null, true, false, 100, 6.18, "abc"])"), STRING("$[2]")},
diff --git a/regression-test/data/json_p0/test_json_load_and_function.out b/regression-test/data/json_p0/test_json_load_and_function.out
@@ -783,7 +783,7 @@
 
 -- !select --
 1	\N	\N
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -884,7 +884,7 @@
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 26	\N	\N
@@ -7023,7 +7023,7 @@ false
 34	{"":1,"ab":"v1"," ":"v1","  ":2}	\N
 
 -- !select --
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -7118,7 +7118,7 @@ false
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 27	{"k1":"v1","k2":200}	{"k1":"v1","k2":200}
diff --git a/regression-test/data/json_p0/test_json_load_unique_key_and_function.out b/regression-test/data/json_p0/test_json_load_unique_key_and_function.out
@@ -619,7 +619,7 @@
 
 -- !select --
 1	\N	\N
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -702,7 +702,7 @@
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 26	\N	\N
diff --git a/regression-test/data/jsonb_p0/test_jsonb_load_and_function.out b/regression-test/data/jsonb_p0/test_jsonb_load_and_function.out
@@ -925,7 +925,7 @@
 
 -- !jsonb_extract_string_select --
 1	\N	\N
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -1026,7 +1026,7 @@
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 26	\N	\N
diff --git a/regression-test/data/jsonb_p0/test_jsonb_load_unique_key_and_function.out b/regression-test/data/jsonb_p0/test_jsonb_load_unique_key_and_function.out
@@ -734,7 +734,7 @@
 
 -- !jsonb_extract_string_select --
 1	\N	\N
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -817,7 +817,7 @@
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 26	\N	\N
diff --git a/regression-test/data/nereids_function_p0/scalar_function/J.out b/regression-test/data/nereids_function_p0/scalar_function/J.out
@@ -827,7 +827,7 @@
 
 -- !jsonb_extract_string_select --
 1	\N	\N
-2	null	null
+2	null	\N
 3	true	true
 4	false	false
 5	100	100
@@ -919,7 +919,7 @@
 13	[]	\N
 14	[123,456]	123
 15	["abc","def"]	abc
-16	[null,true,false,100,6.18,"abc"]	null
+16	[null,true,false,100,6.18,"abc"]	\N
 17	[{"k1":"v41","k2":400},1,"a",3.14]	{"k1":"v41","k2":400}
 18	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}	{"k1":"v31","k2":300,"a1":[{"k1":"v41","k2":400},1,"a",3.14]}
 26	\N	\N
diff --git a/regression-test/data/query_p0/sql_functions/json_functions/test_json_extract.out b/regression-test/data/query_p0/sql_functions/json_functions/test_json_extract.out
@@ -0,0 +1,22 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql_string1 --
+v31
+
+-- !sql_string2 --
+\N
+
+-- !sql_string3 --
+\N
+
+-- !sql_string4 --
+1234.56
+
+-- !sql_string5 --
+2025-06-05 14:47:01
+
+-- !sql_string6 --
+\N
+
+-- !sql_string7 --
+\N
+
diff --git a/regression-test/suites/query_p0/sql_functions/json_functions/test_json_extract.groovy b/regression-test/suites/query_p0/sql_functions/json_functions/test_json_extract.groovy
@@ -0,0 +1,31 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+suite("test_json_extract") {
+    qt_sql_string1 """ SELECT JSON_EXTRACT_STRING('{"k1":"v31","k2":300}', '\$.k1'); """
+    qt_sql_string2 """ SELECT JSON_EXTRACT_STRING(null, '\$.k1'); """
+    qt_sql_string3 """ SELECT JSON_EXTRACT_STRING('{"k1":"v31","k2":300}', NULL); """
+    qt_sql_string4 """ SELECT JSON_EXTRACT_STRING('{"k1":"v31","k2":{"sub_key": 1234.56}}', '\$.k2.sub_key'); """
+    qt_sql_string5 """ SELECT JSON_EXTRACT_STRING(json_array("abc", 123, STR_TO_DATE('2025-06-05 14:47:01', '%Y-%m-%d %H:%i:%s')), '\$.[2]'); """
+    qt_sql_string6 """ SELECT JSON_EXTRACT_STRING('{"k1":"v31","k2": null}', '\$.k2'); """
+    qt_sql_string7 """ SELECT JSON_EXTRACT_STRING('{"k1":"v31","k2":300}', '\$.k3'); """
+
+    test {
+        sql """ SELECT JSON_EXTRACT_STRING('{"id": 123, "name": "doris"}', '\$.'); """
+        exception "Invalid Json Path for value: \$."
+    }
+}
