expression: unset the flen for string type builtin control (#38845) (#…

…38849)

close #38844

expression/builtin_control.go

@@ -147,7 +147,11 @@ func InferType4ControlFuncs(ctx sessionctx.Context, funcName string, lexp, rexp
 			}
 			flen := maxlen(lhsFlen, rhsFlen) + resultFieldType.GetDecimal() + 1 // account for -1 len fields
 			resultFieldType.SetFlen(mathutil.Min(flen, mysql.MaxDecimalWidth))  // make sure it doesn't overflow
-
+		} else if evalType == types.ETString {
+			lhsLen, rhsLen := lhs.GetFlen(), rhs.GetFlen()
+			if lhsLen != types.UnspecifiedLength && rhsLen != types.UnspecifiedLength {
+				resultFieldType.SetFlen(mathutil.Max(lhsLen, rhsLen))
+			}
 		} else {
 			resultFieldType.SetFlen(maxlen(lhs.GetFlen(), rhs.GetFlen()))
 		}

expression/integration_test.go

@@ -7394,3 +7394,15 @@ func TestIssue31569(t *testing.T) {
 	tk.MustQuery("show warnings").Check([][]interface{}{})
 	tk.MustExec("drop table t")
 }
+
+func TestIfNullParamMarker(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t (c1 varchar(100), c2 varchar(128));")
+	tk.MustExec(`prepare pr1 from "insert into t values(ifnull(?,' '),ifnull(?,' '))";`)
+	tk.MustExec(`set @a='1',@b=repeat('x', 80);`)
+	// Should not report 'Data too long for column' error.
+	tk.MustExec(`execute pr1 using @a,@b;`)
+}