cherry pick #21849 to release-4.0 (#21960)

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

Co-authored-by: Zhi Qi <30543181+LittleFall@users.noreply.github.com>
Co-authored-by: Kenan Yao <cauchy1992@gmail.com>

executor/seqtest/prepared_test.go

@@ -741,19 +741,39 @@ func (s *seqTestSuite) TestPreparedIssue8644(c *C) {
 		c.Assert(err, IsNil)
 
 		tk.MustExec("use test")
+
 		tk.MustExec("drop table if exists t")
 		tk.MustExec("create table t(data mediumblob)")
-
-		tk.MustExec(`prepare stmt1 from 'insert t (data) values (?)'`)
-
+		tk.MustExec(`prepare stmt from 'insert t (data) values (?)'`)
 		tk.MustExec(`set @a = 'a'`)
-		tk.MustExec(`execute stmt1 using @a;`)
-
+		tk.MustExec(`execute stmt using @a;`)
 		tk.MustExec(`set @b = 'aaaaaaaaaaaaaaaaaa'`)
-		tk.MustExec(`execute stmt1 using @b;`)
+		tk.MustExec(`execute stmt using @b;`)
 
 		r := tk.MustQuery(`select * from t`)
 		r.Check(testkit.Rows("a", "aaaaaaaaaaaaaaaaaa"))
+
+		tk.MustExec("drop table if exists t")
+		tk.MustExec("create table t(data decimal)")
+		tk.MustExec(`prepare stmt from 'insert t (data) values (?)'`)
+		tk.MustExec(`set @a = '1'`)
+		tk.MustExec(`execute stmt using @a;`)
+		tk.MustExec(`set @b = '11111.11111'`) // '.11111' will be truncated.
+		tk.MustExec(`execute stmt using @b;`)
+
+		r = tk.MustQuery(`select * from t`)
+		r.Check(testkit.Rows("1", "11111"))
+
+		tk.MustExec("drop table if exists t")
+		tk.MustExec("create table t(data decimal(10,3));")
+		tk.MustExec("prepare stmt from 'insert t (data) values (?)';")
+		tk.MustExec("set @a = 1.1;")
+		tk.MustExec("execute stmt using @a;")
+		tk.MustExec("set @b = 11.11;")
+		tk.MustExec("execute stmt using @b;")
+
+		r = tk.MustQuery(`select * from t`)
+		r.Check(testkit.Rows("1.100", "11.110"))
 	}
 }
 

types/field_type.go

@@ -184,7 +184,7 @@ func DefaultParamTypeForValue(value interface{}, tp *FieldType) {
 func hasVariantFieldLength(tp *FieldType) bool {
 	switch tp.Tp {
 	case mysql.TypeLonglong, mysql.TypeVarString, mysql.TypeDouble, mysql.TypeBlob,
-		mysql.TypeBit, mysql.TypeDuration, mysql.TypeNewDecimal, mysql.TypeEnum, mysql.TypeSet:
+		mysql.TypeBit, mysql.TypeDuration, mysql.TypeEnum, mysql.TypeSet:
 		return true
 	}
 	return false