session: fix global variable collation_server does not take effect in new session

session/session.go

@@ -2570,7 +2570,7 @@ func (s *session) loadCommonGlobalVariablesIfNeeded() error {
 			vars = append(vars, variable.PluginVarNames...)
 		}
 
-		stmt, err := s.ParseWithParams(context.TODO(), "select HIGH_PRIORITY * from mysql.global_variables where variable_name in (%?)", vars)
+		stmt, err := s.ParseWithParams(context.TODO(), "select HIGH_PRIORITY * from mysql.global_variables where variable_name in (%?) order by VARIABLE_NAME", vars)
 		if err != nil {
 			return nil, nil, errors.Trace(err)
 		}
@@ -2588,7 +2588,9 @@ func (s *session) loadCommonGlobalVariablesIfNeeded() error {
 	for _, row := range rows {
 		varName := row.GetString(0)
 		varVal := row.GetDatum(1, &fields[1].Column.FieldType)
-		if _, ok := vars.GetSystemVar(varName); !ok {
+		// `collation_server` is related to `character_set_server`, set `character_set_server` will also set `collation_server`.
+		// We have to make sure we set the `collation_server` with right value.
+		if _, ok := vars.GetSystemVar(varName); !ok || varName == variable.CollationServer {
 			err = variable.SetSessionSystemVar(s.sessionVars, varName, varVal)
 			if err != nil {
 				return err

session/session_test.go

@@ -4171,6 +4171,15 @@ func (s *testSessionSerialSuite) TestTiKVSystemVars(c *C) {
 
 }
 
+func (s *testSessionSerialSuite) TestGlobalVarCollationServer(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("set @@global.collation_server=utf8mb4_general_ci")
+	tk.MustQuery("show global variables like 'collation_server'").Check(testkit.Rows("collation_server utf8mb4_general_ci"))
+	tk = testkit.NewTestKit(c, s.store)
+	tk.MustQuery("show global variables like 'collation_server'").Check(testkit.Rows("collation_server utf8mb4_general_ci"))
+	tk.MustQuery("show variables like 'collation_server'").Check(testkit.Rows("collation_server utf8mb4_general_ci"))
+}
+
 func (s *testSessionSerialSuite) TestProcessInfoIssue22068(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")