fix(query): fix variant get string function auto cast null to SQL NULL

src/query/functions/src/scalars/variant.rs

@@ -394,8 +394,12 @@ pub fn register(registry: &mut FunctionRegistry) {
                 }
                 match get_by_name(val, name, false) {
                     Some(v) => {
-                        let json_str = cast_to_string(&v);
-                        output.push(&json_str);
+                        if is_null(&v) {
+                            output.push_null();
+                        } else {
+                            let json_str = cast_to_string(&v);
+                            output.push(&json_str);
+                        }
                     }
                     None => output.push_null(),
                 }
@@ -419,8 +423,12 @@ pub fn register(registry: &mut FunctionRegistry) {
                 } else {
                     match get_by_index(val, idx as usize) {
                         Some(v) => {
-                            let json_str = cast_to_string(&v);
-                            output.push(&json_str);
+                            if is_null(&v) {
+                                output.push_null();
+                            } else {
+                                let json_str = cast_to_string(&v);
+                                output.push(&json_str);
+                            }
                         }
                         None => {
                             output.push_null();
@@ -632,7 +640,7 @@ pub fn register(registry: &mut FunctionRegistry) {
                                 let mut out_offsets = Vec::new();
                                 match get_by_path(&buf, json_path, &mut out_buf, &mut out_offsets) {
                                     Ok(()) => {
-                                        if out_offsets.is_empty() {
+                                        if out_offsets.is_empty() || is_null(&out_buf) {
                                             output.push_null();
                                         } else {
                                             let json_str = cast_to_string(&out_buf);

src/query/functions/tests/it/scalars/testdata/variant.txt

@@ -900,6 +900,15 @@ output domain  : {"{\"b\":2}"..="{\"b\":2}"}
 output         : '{"b":2}'
 
 
+ast            : json_extract_path_text('{"a":null}', 'a')
+raw expr       : json_extract_path_text('{"a":null}', 'a')
+checked expr   : json_extract_path_text<String, String>("{\"a\":null}", "a")
+optimized expr : NULL
+output type    : String NULL
+output domain  : {NULL}
+output         : NULL
+
+
 ast            : json_extract_path_text(s, k)
 raw expr       : json_extract_path_text(s::String, k::String)
 checked expr   : json_extract_path_text<String, String>(s, k)
@@ -3283,6 +3292,15 @@ output domain  : {NULL}
 output         : NULL
 
 
+ast            : parse_json('{"k":null}')->>'k'
+raw expr       : get_string(parse_json('{"k":null}'), 'k')
+checked expr   : get_string<Variant, String>(parse_json<String>("{\"k\":null}"), "k")
+optimized expr : NULL
+output type    : String NULL
+output domain  : {NULL}
+output         : NULL
+
+
 ast            : CAST(('a', 'b') AS VARIANT)->>'2'
 raw expr       : get_string(CAST(tuple('a', 'b') AS Variant), '2')
 checked expr   : get_string<Variant, String>(to_variant<T0=Tuple(String, String)><T0>(tuple<String, String>("a", "b")), "2")

src/query/functions/tests/it/scalars/variant.rs

@@ -326,6 +326,7 @@ fn test_get_string_arrow_op(file: &mut impl Write) {
     run_ast(file, "parse_json('[1,2,3,4]')->>(2+3)", &[]);
     run_ast(file, "parse_json('{\"k\":\"v\"}')->>'k'", &[]);
     run_ast(file, "parse_json('{\"k\":\"v\"}')->>'x'", &[]);
+    run_ast(file, "parse_json('{\"k\":null}')->>'k'", &[]);
     run_ast(file, "CAST(('a', 'b') AS VARIANT)->>'2'", &[]);
 
     run_ast(file, "parse_json(s)->>i", &[
@@ -471,6 +472,7 @@ fn test_json_extract_path_text(file: &mut impl Write) {
     );
     run_ast(file, "json_extract_path_text('{\"a\":{\"b\":2}}', 'a')", &[
     ]);
+    run_ast(file, "json_extract_path_text('{\"a\":null}', 'a')", &[]);
 
     run_ast(file, "json_extract_path_text(s, k)", &[
         (

tests/sqllogictests/suites/query/functions/02_0051_function_semi_structureds_get.test

@@ -92,13 +92,18 @@ NULL
 query T
 select parse_json('{"aa": null, "aA": 2, "Aa": 3}')->>'aa'
 ----
-null
+NULL
 
 query T
 select parse_json(null)->>'aa'
 ----
 NULL
 
+query T
+select parse_json('{"key1":null}')->>'key1'
+----
+NULL
+
 query T
 select parse_json('[2.71, 3.14]')[0]
 ----
@@ -201,6 +206,10 @@ select json_extract_path_text('{"customer":{"id": 1, "name":"databend", "extras"
 ----
 {"customer":{"extras":["ext","test"],"id":1,"name":"databend"}}
 
+query T
+select json_extract_path_text('{"attr":null}', 'attr')
+----
+NULL
 
 query T
 select NULL#>'{0}'