executor: fix wrong behavior of set charset statement (#16984)

executor/set.go

@@ -60,10 +60,10 @@ func (e *SetExecutor) Next(ctx context.Context, req *chunk.Chunk) error {
 	sessionVars := e.ctx.GetSessionVars()
 	for _, v := range e.vars {
 		// Variable is case insensitive, we use lower case.
-		if v.Name == ast.SetNames {
+		if v.Name == ast.SetNames || v.Name == ast.SetCharset {
 			// This is set charset stmt.
 			if v.IsDefault {
-				err := e.setCharset(mysql.DefaultCharset, "")
+				err := e.setCharset(mysql.DefaultCharset, "", v.Name == ast.SetNames)
 				if err != nil {
 					return err
 				}
@@ -78,7 +78,7 @@ func (e *SetExecutor) Next(ctx context.Context, req *chunk.Chunk) error {
 			if v.ExtendValue != nil {
 				co = v.ExtendValue.Value.GetString()
 			}
-			err = e.setCharset(cs, co)
+			err = e.setCharset(cs, co, v.Name == ast.SetNames)
 			if err != nil {
 				return err
 			}
@@ -240,7 +240,7 @@ func (e *SetExecutor) setSysVariable(name string, v *expression.VarAssignment) e
 	return nil
 }
 
-func (e *SetExecutor) setCharset(cs, co string) error {
+func (e *SetExecutor) setCharset(cs, co string, isSetName bool) error {
 	var err error
 	if len(co) == 0 {
 		if co, err = charset.GetDefaultCollation(cs); err != nil {
@@ -256,12 +256,33 @@ func (e *SetExecutor) setCharset(cs, co string) error {
 		}
 	}
 	sessionVars := e.ctx.GetSessionVars()
-	for _, v := range variable.SetNamesVariables {
+	if isSetName {
+		for _, v := range variable.SetNamesVariables {
+			if err = sessionVars.SetSystemVar(v, cs); err != nil {
+				return errors.Trace(err)
+			}
+		}
+		return errors.Trace(sessionVars.SetSystemVar(variable.CollationConnection, co))
+	}
+	// Set charset statement, see also https://dev.mysql.com/doc/refman/8.0/en/set-character-set.html.
+	for _, v := range variable.SetCharsetVariables {
 		if err = sessionVars.SetSystemVar(v, cs); err != nil {
 			return errors.Trace(err)
 		}
 	}
-	return sessionVars.SetSystemVar(variable.CollationConnection, co)
+	csDb, err := sessionVars.GlobalVarsAccessor.GetGlobalSysVar(variable.CharsetDatabase)
+	if err != nil {
+		return err
+	}
+	coDb, err := sessionVars.GlobalVarsAccessor.GetGlobalSysVar(variable.CollationDatabase)
+	if err != nil {
+		return err
+	}
+	err = sessionVars.SetSystemVar(variable.CharacterSetConnection, csDb)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	return errors.Trace(sessionVars.SetSystemVar(variable.CollationConnection, coDb))
 }
 
 func (e *SetExecutor) getVarValue(v *expression.VarAssignment, sysVar *variable.SysVar) (value types.Datum, err error) {

executor/set_test.go

@@ -542,7 +542,7 @@ func (s *testSuite5) TestSetCharset(c *C) {
 	tk.MustExec(`SET CHARACTER SET latin1`)
 	check(
 		"latin1",
-		"latin1",
+		"utf8mb4",
 		"latin1",
 		"utf8mb4",
 		"utf8mb4",

go.mod

@@ -32,7 +32,7 @@ require (
 	github.com/pingcap/goleveldb v0.0.0-20191226122134-f82aafb29989
 	github.com/pingcap/kvproto v0.0.0-20200706115936-1e0910aabe6c
 	github.com/pingcap/log v0.0.0-20200511115504-543df19646ad
-	github.com/pingcap/parser v0.0.0-20200623164729-3a18f1e5dceb
+	github.com/pingcap/parser v0.0.0-20200708150102-420619df5c94
 	github.com/pingcap/pd/v4 v4.0.0-rc.2.0.20200520083007-2c251bd8f181
 	github.com/pingcap/sysutil v0.0.0-20200408114249-ed3bd6f7fdb1
 	github.com/pingcap/tidb-tools v4.0.1-0.20200530144555-cdec43635625+incompatible

go.sum

@@ -421,8 +421,9 @@ github.com/pingcap/log v0.0.0-20200511115504-543df19646ad/go.mod h1:4rbK1p9ILyIf
 github.com/pingcap/parser v0.0.0-20200424075042-8222d8b724a4/go.mod h1:9v0Edh8IbgjGYW2ArJr19E+bvL8zKahsFp+ixWeId+4=
 github.com/pingcap/parser v0.0.0-20200507022230-f3bf29096657/go.mod h1:9v0Edh8IbgjGYW2ArJr19E+bvL8zKahsFp+ixWeId+4=
 github.com/pingcap/parser v0.0.0-20200603032439-c4ecb4508d2f/go.mod h1:9v0Edh8IbgjGYW2ArJr19E+bvL8zKahsFp+ixWeId+4=
-github.com/pingcap/parser v0.0.0-20200623164729-3a18f1e5dceb h1:v9iX5qIr8nG3QxMtlcTT+1DI0YD4HqABy7tuohbp28E=
 github.com/pingcap/parser v0.0.0-20200623164729-3a18f1e5dceb/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
+github.com/pingcap/parser v0.0.0-20200708150102-420619df5c94 h1:2ClwFuxJTpDMdjJesnr4bGX4uNRIMl6h8mN1gulFc2M=
+github.com/pingcap/parser v0.0.0-20200708150102-420619df5c94/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
 github.com/pingcap/pd/v4 v4.0.0-rc.1.0.20200422143320-428acd53eba2/go.mod h1:s+utZtXDznOiL24VK0qGmtoHjjXNsscJx3m1n8cC56s=
 github.com/pingcap/pd/v4 v4.0.0-rc.2.0.20200520083007-2c251bd8f181 h1:FM+PzdoR3fmWAJx3ug+p5aOgs5aZYwFkoDL7Potdsz0=
 github.com/pingcap/pd/v4 v4.0.0-rc.2.0.20200520083007-2c251bd8f181/go.mod h1:q4HTx/bA8aKBa4S7L+SQKHvjRPXCRV0tA0yRw0qkZSA=

sessionctx/variable/sysvar.go

@@ -748,6 +748,12 @@ var SetNamesVariables = []string{
 	"character_set_results",
 }
 
+// SetCharsetVariables is the system variable names related to set charset statements.
+var SetCharsetVariables = []string{
+	"character_set_client",
+	"character_set_results",
+}
+
 const (
 	// CharacterSetConnection is the name for character_set_connection system variable.
 	CharacterSetConnection = "character_set_connection"