planner, executor: fix tp.Flen size when union with castIntAsString (#…

…8442) (#8491)

executor/executor_test.go

@@ -1062,6 +1062,12 @@ func (s *testSuite) TestUnion(c *C) {
 	tk.MustExec("CREATE TABLE t2 (a int not null, b char (10) not null)")
 	tk.MustExec("insert into t2 values(1,'a'),(2,'b'),(3,'c'),(3,'c')")
 	tk.MustQuery("select a from t1 union select a from t1 order by (select a+1);").Check(testkit.Rows("1", "2", "3"))
+
+	// #issue 8231
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec("CREATE TABLE t1 (uid int(1))")
+	tk.MustExec("INSERT INTO t1 SELECT 150")
+	tk.MustQuery("SELECT 'a' UNION SELECT uid FROM t1 order by 1 desc;").Check(testkit.Rows("a", "150"))
 }
 
 func (s *testSuite) TestNeighbouringProj(c *C) {

plan/logical_plan_builder.go

@@ -630,6 +630,9 @@ func joinFieldType(a, b *types.FieldType) *types.FieldType {
 	resultTp.Decimal = mathutil.Max(a.Decimal, b.Decimal)
 	// `Flen - Decimal` is the fraction before '.'
 	resultTp.Flen = mathutil.Max(a.Flen-a.Decimal, b.Flen-b.Decimal) + resultTp.Decimal
+	if resultTp.EvalType() != types.ETInt && (a.EvalType() == types.ETInt || b.EvalType() == types.ETInt) && resultTp.Flen < mysql.MaxIntWidth {
+		resultTp.Flen = mysql.MaxIntWidth
+	}
 	resultTp.Charset = a.Charset
 	resultTp.Collate = a.Collate
 	expression.SetBinFlagOrBinStr(b, resultTp)