[Enhancement] to_json return null when unsupported (backport #45607)

be/src/exprs/cast_expr.h

@@ -194,7 +194,7 @@ struct CastToString {
     }
 };
 
-StatusOr<ColumnPtr> cast_nested_to_json(const ColumnPtr& column);
+StatusOr<ColumnPtr> cast_nested_to_json(const ColumnPtr& column, bool allow_throw_exception);
 
 // cast column[idx] to coresponding json type.
 StatusOr<std::string> cast_type_to_json_str(const ColumnPtr& column, int idx);

be/src/exprs/cast_expr_json.cpp

@@ -134,7 +134,7 @@ class CastColumnItemVisitor final : public ColumnVisitorAdapter<CastColumnItemVi
         auto val_col = col.values_column();
 
         if (key_col->has_null()) {
-            return Status::NotSupported("key of Map should not be nullable");
+            return Status::NotSupported("key of Map should not be null");
         }
         if (key_col->is_nullable()) {
             key_col = ColumnHelper::as_column<NullableColumn>(key_col)->data_column();
@@ -216,20 +216,38 @@ class CastColumnItemVisitor final : public ColumnVisitorAdapter<CastColumnItemVi
 
 // Cast nested type(including struct/map/* to json)
 // TODO(murphy): optimize the performance with columnwise-casting
-StatusOr<ColumnPtr> cast_nested_to_json(const ColumnPtr& column) {
+StatusOr<ColumnPtr> cast_nested_to_json(const ColumnPtr& column, bool allow_throw_exception) {
     ColumnBuilder<TYPE_JSON> column_builder(column->size());
     vpack::Builder json_builder;
-    for (int row = 0; row < column->size(); row++) {
-        if (column->is_null(row)) {
-            column_builder.append_null();
-            continue;
+    if (allow_throw_exception) {
+        for (int row = 0; row < column->size(); row++) {
+            if (column->is_null(row)) {
+                column_builder.append_null();
+                continue;
+            }
+            json_builder.clear();
+            RETURN_IF_ERROR(CastColumnItemVisitor::cast_datum_to_json(column, row, "", &json_builder));
+            JsonValue json(json_builder.slice());
+            column_builder.append(std::move(json));
         }
-        json_builder.clear();
-        RETURN_IF_ERROR(CastColumnItemVisitor::cast_datum_to_json(column, row, "", &json_builder));
+    } else {
+        for (int row = 0; row < column->size(); row++) {
+            if (column->is_null(row)) {
+                column_builder.append_null();
+                continue;
+            }
+            json_builder.clear();
+            auto st = CastColumnItemVisitor::cast_datum_to_json(column, row, "", &json_builder);
+            if (!st.ok()) {
+                column_builder.append_null();
+                continue;
+            }
 
-        JsonValue json(json_builder.slice());
-        column_builder.append(std::move(json));
+            JsonValue json(json_builder.slice());
+            column_builder.append(std::move(json));
+        }
     }
+
     return column_builder.build(false);
 }
 

be/src/exprs/function_context.cpp

@@ -169,6 +169,10 @@ bool FunctionContext::error_if_overflow() const {
     return _state != nullptr && _state->error_if_overflow();
 }
 
+bool FunctionContext::allow_throw_exception() const {
+    return _state != nullptr && _state->query_options().allow_throw_exception;
+}
+
 void FunctionContext::set_function_state(FunctionStateScope scope, void* ptr) {
     switch (scope) {
     case THREAD_LOCAL:

be/src/exprs/function_context.h

@@ -177,6 +177,8 @@ class FunctionContext {
 
     bool error_if_overflow() const;
 
+    bool allow_throw_exception() const;
+
     std::unique_ptr<NgramBloomFilterState>& get_ngram_state() { return _ngramState; }
 
 private:

be/src/exprs/json_functions.cpp

@@ -1085,7 +1085,7 @@ StatusOr<ColumnPtr> JsonFunctions::_json_keys_without_path(FunctionContext* cont
 
 StatusOr<ColumnPtr> JsonFunctions::to_json(FunctionContext* context, const Columns& columns) {
     RETURN_IF_COLUMNS_ONLY_NULL(columns);
-    return cast_nested_to_json(columns[0]);
+    return cast_nested_to_json(columns[0], context->allow_throw_exception());
 }
 
 } // namespace starrocks

test/sql/test_json/R/to_json

@@ -33,4 +33,12 @@ SELECT to_json(row(1, 1));
 SELECT to_json(NULL);
 -- result:
 None
--- !result
+-- !result
+select /*+SET_VAR(sql_mode='ONLY_FULL_GROUP_BY,ALLOW_THROW_EXCEPTION')*/ to_json(map{null:null});
+-- result:
+E: (1064, 'key of Map should not be null')
+-- !result
+select /*+SET_VAR(sql_mode='ONLY_FULL_GROUP_BY')*/ to_json(map{null:null});
+-- result:
+None
+-- !result

test/sql/test_json/T/to_json

@@ -16,4 +16,7 @@ INSERT INTO t0 VALUES (2, row(1, 1));
 select to_json(c1) from t0 order by c0;
 
 SELECT to_json(row(1, 1));
-SELECT to_json(NULL);
+SELECT to_json(NULL);
+
+select /*+SET_VAR(sql_mode='ONLY_FULL_GROUP_BY,ALLOW_THROW_EXCEPTION')*/ to_json(map{null:null});
+select /*+SET_VAR(sql_mode='ONLY_FULL_GROUP_BY')*/ to_json(map{null:null});