cherry pick pingcap#22785 to release-5.0-rc

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

expression/expression.go

@@ -458,8 +458,20 @@ func toBool(sc *stmtctx.StatementContext, tp *types.FieldType, eType types.EvalT
 				sVal := buf.GetString(i)
 				if tp.Hybrid() {
 					switch tp.Tp {
-					case mysql.TypeEnum, mysql.TypeSet:
+					case mysql.TypeSet, mysql.TypeEnum:
 						fVal = float64(len(sVal))
+						if fVal == 0 {
+							// The elements listed in the column specification are assigned index numbers, beginning
+							// with 1. The index value of the empty string error value (distinguish from a "normal"
+							// empty string) is 0. Thus we need to check whether it's an empty string error value when
+							// `fVal==0`.
+							for idx, elem := range tp.Elems {
+								if elem == sVal {
+									fVal = float64(idx + 1)
+									break
+								}
+							}
+						}
 					case mysql.TypeBit:
 						var bl types.BinaryLiteral = buf.GetBytes(i)
 						iVal, err := bl.ToInt(sc)

expression/integration_test.go

@@ -8432,3 +8432,47 @@ func (s *testIntegrationSuite) TestIssue22098(c *C) {
 	tk.MustExec("set @a=3;set @b=20200414;set @c='a';set @d=20200414;set @e=3;set @f='a';")
 	tk.MustQuery("execute stmt using @a,@b,@c,@d,@e,@f").Check(testkit.Rows())
 }
+<<<<<<< HEAD
+=======
+
+func (s *testIntegrationSerialSuite) TestCollationUnion2(c *C) {
+	// For issue 22179
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a varchar(10))")
+	tk.MustExec("insert into t values('aaaaaaaaa'),('天王盖地虎宝塔镇河妖')")
+	tk.MustQuery("select * from t").Check(testkit.Rows("aaaaaaaaa", "天王盖地虎宝塔镇河妖"))
+
+	// check the collation of sub query of union statement.
+	tk.MustQuery("select collation(a) from (select null as a) aaa").Check(testkit.Rows("binary"))
+	tk.MustQuery("select collation(a) from (select a from t limit 1) aaa").Check(testkit.Rows("utf8mb4_bin"))
+
+	// Reverse sub query of union statement.
+	tk.MustQuery("select * from (select null as a union all select a from t) aaa order by a").Check(testkit.Rows("<nil>", "aaaaaaaaa", "天王盖地虎宝塔镇河妖"))
+	tk.MustQuery("select * from (select a from t) aaa union all select null as a order by a").Check(testkit.Rows("<nil>", "aaaaaaaaa", "天王盖地虎宝塔镇河妖"))
+	tk.MustExec("drop table if exists t")
+}
+
+func (s *testIntegrationSuite) Test22717(c *C) {
+	// For issue 22717
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec(`create table t(
+					 	a enum('a','','c'),
+						b enum('0','1','2'),
+						c set('a','','c'),
+						d set('0','1','2')
+					 )`)
+	tk.MustExec("insert into t values(1,1,1,1),(2,2,2,2),(3,3,3,3)")
+	tk.MustExec("set @@sql_mode = ''")
+	tk.MustExec("insert into t values('','','','')")
+	tk.MustQuery("select * from t").Check(testkit.Rows("a 0 a 0", " 1  1", "c 2 a, 0,1", "   "))
+	tk.MustQuery("select a from t where a").Check(testkit.Rows("a", "", "c", ""))
+	tk.MustQuery("select b from t where b").Check(testkit.Rows("0", "1", "2"))
+	tk.MustQuery("select c from t where c").Check(testkit.Rows("a", "", "a,", ""))
+	tk.MustQuery("select d from t where d").Check(testkit.Rows("0", "1", "0,1"))
+}
+>>>>>>> 8c2db1b93... expression: fix enum and set type expression in where clause (#22785)