expression: fix unexpected error msg for cast string to decimal

expression/builtin_cast.go

@@ -1440,7 +1440,11 @@ func (b *builtinCastStringAsDecimalSig) evalDecimal(row chunk.Row) (res *types.M
 	res = new(types.MyDecimal)
 	sc := b.ctx.GetSessionVars().StmtCtx
 	if !(b.inUnion && mysql.HasUnsignedFlag(b.tp.GetFlag()) && isNegative) {
-		err = sc.HandleTruncate(res.FromString([]byte(val)))
+		err = res.FromString([]byte(val))
+		if err == types.ErrTruncated {
+			err = types.ErrTruncatedWrongVal.GenWithStackByArgs("DECIMAL", []byte(val))
+		}
+		err = sc.HandleTruncate(err)
 		if err != nil {
 			return res, false, err
 		}

tests/integrationtest/r/expression/cast.result

@@ -78,3 +78,13 @@ select cast(col4 as time(31)) from t where col1 is null;
 Error 1426 (42000): Too big precision 31 specified for column 'CAST'. Maximum is 6.
 select cast(col5 as time(31)) from t where col1 is null;
 Error 1426 (42000): Too big precision 31 specified for column 'CAST'. Maximum is 6.
+drop table if exists t1;
+create table t1 (c1 text);
+insert into t1 values ('a');
+update t1 set c1 = cast('61qw' as decimal);
+Error 1292 (22007): Truncated incorrect DECIMAL value: '61qw'
+select cast('61qw' as decimal);
+cast('61qw' as decimal)
+61
+Level	Code	Message
+Warning	1292	Truncated incorrect DECIMAL value: '61qw'

tests/integrationtest/t/expression/cast.test

@@ -45,3 +45,13 @@ select cast(col3 as time(31)) from t where col1 is null;
 select cast(col4 as time(31)) from t where col1 is null;
 -- error 1426
 select cast(col5 as time(31)) from t where col1 is null;
+
+# TestCastErrMsg
+drop table if exists t1;
+create table t1 (c1 text);
+insert into t1 values ('a');
+--error 1292
+update t1 set c1 = cast('61qw' as decimal);
+--enable_warnings
+select cast('61qw' as decimal);
+--disable_warnings