expression,json: make the behavior of JSON_VALID consistent (#57496) (

#57505)

close #56293

pkg/expression/builtin_json.go

@@ -1038,7 +1038,8 @@ func (b *builtinJSONValidOthersSig) Clone() builtinFunc {
 // evalInt evals a builtinJSONValidOthersSig.
 // See https://dev.mysql.com/doc/refman/5.7/en/json-attribute-functions.html#function_json-valid
 func (b *builtinJSONValidOthersSig) evalInt(ctx EvalContext, row chunk.Row) (val int64, isNull bool, err error) {
-	return 0, false, nil
+	datum, err := b.args[0].Eval(ctx, row)
+	return 0, datum.IsNull(), err
 }
 
 type jsonArrayAppendFunctionClass struct {

tests/integrationtest/r/expression/json.result

@@ -765,3 +765,9 @@ Error 3853 (22032): Invalid JSON type in argument 1 to function json_schema_vali
 select json_type(cast(cast('2024' as year) as json));
 json_type(cast(cast('2024' as year) as json))
 UNSIGNED INTEGER
+drop table if exists t;
+create table t(j json, str varchar(255), other int);
+insert into t values (NULL, NULL, NULL);
+select json_valid(j), json_valid(str), json_valid(other) from t;
+json_valid(j)	json_valid(str)	json_valid(other)
+NULL	NULL	NULL

tests/integrationtest/t/expression/json.test

@@ -484,3 +484,9 @@ SELECT JSON_SCHEMA_VALID('{"properties": {"a": {"exclusiveMinimum": true}}}', '{
 # TestIssue54494
 # https://github.com/pingcap/tidb/issues/54494
 select json_type(cast(cast('2024' as year) as json));
+
+# TestJSONValidForNull
+drop table if exists t;
+create table t(j json, str varchar(255), other int);
+insert into t values (NULL, NULL, NULL);
+select json_valid(j), json_valid(str), json_valid(other) from t;