This is an automated cherry-pick of pingcap#61080

Signed-off-by: ti-chi-bot <[email protected]>
Signed-off-by: xhe <[email protected]>

Author: xhebox

cmd/explaintest/t/new_character_set.test

@@ -67,3 +67,14 @@ set names utf8mb4;
 set @@character_set_client=gbk;
 set @@character_set_connection=gbk;
 select hex('一a'), '一a';
+
+-- 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;
+create table t61085 (a char(255) charset gbk);
+insert into t61085 values ('AAA');
+set SESSION sql_mode = '';
+--error 1105
+select * from t61085 where a = cast(0x41414180424242 as char charset gbk);
+DROP TABLE t61085;

server/util.go

@@ -385,7 +385,7 @@ func (d *resultEncoder) encodeData(src []byte) []byte {
 }
 
 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))
 	}