server: replace instead of truncate encoded result (#61080) (#61195)

close #61085

Author: ti-chi-bot

pkg/server/internal/column/result_encoder.go

@@ -124,7 +124,7 @@ func (d *ResultEncoder) EncodeData(src []byte) []byte {
 
 // EncodeWith encodes bytes with the given encoding.
 func (d *ResultEncoder) EncodeWith(src []byte, enc charset.Encoding) []byte {
-	data, err := enc.Transform(d.buffer, src, charset.OpEncode)
+	data, err := enc.Transform(d.buffer, src, charset.OpEncodeReplace)
 	if err != nil {
 		logutil.BgLogger().Debug("encode error", zap.Error(err))
 	}

tests/integrationtest/r/new_character_set.result

@@ -112,3 +112,16 @@ set names utf8mb4;
 show variables like 'collation_connection';
 Variable_name	Value
 collation_connection	utf8mb4_bin
+set character_set_results = "gbk";
+select cast(0x414141E280A9424242 as char charset utf8mb4);
+cast(0x414141E280A9424242 as char charset utf8mb4)
+AAA?BBB
+SET character_set_results = @undefined_var;
+DROP TABLE if exists t61085;
+create table t61085 (a char(255) charset gbk);
+insert into t61085 values ('AAA');
+set SESSION sql_mode = '';
+select * from t61085 where a = cast(0x41414180424242 as char charset gbk);
+a
+AAA
+DROP TABLE t61085;

tests/integrationtest/t/new_character_set.test

@@ -83,3 +83,14 @@ show variables like 'collation_connection';
 set default_collation_for_utf8mb4 = default;
 set names utf8mb4;
 show variables like 'collation_connection';
+
+# Bug#61085: https://github.com/pingcap/tidb/issues/61085 should replace instead of truncation for result charset
+set character_set_results = "gbk";
+select cast(0x414141E280A9424242 as char charset utf8mb4);
+SET character_set_results = @undefined_var;
+DROP TABLE if exists t61085;
+create table t61085 (a char(255) charset gbk);
+insert into t61085 values ('AAA');
+set SESSION sql_mode = '';
+select * from t61085 where a = cast(0x41414180424242 as char charset gbk);
+DROP TABLE t61085;