Add several features that unblock mysql workbench (#573)

enginetest/queries.go

@@ -5328,6 +5328,22 @@ var QueryTests = []QueryTest{
 		Query:    `SELECT EXISTS (SELECT pk FROM one_pk WHERE pk > 4)`,
 		Expected: []sql.Row{{false}},
 	},
+	{
+		Query:    `SHOW STATUS`,
+		Expected: []sql.Row{},
+	},
+	{
+		Query:    `SHOW GLOBAL STATUS`,
+		Expected: []sql.Row{},
+	},
+	{
+		Query:    `SHOW SESSION STATUS`,
+		Expected: []sql.Row{},
+	},
+	{
+		Query:    `SHOW STATUS LIKE 'Bytes_received'`,
+		Expected: []sql.Row{},
+	},
 }
 
 var KeylessQueries = []QueryTest{

enginetest/variable_queries.go

@@ -125,6 +125,36 @@ var VariableQueries = []ScriptTest{
 			{"charset", "charset", "charset"},
 		},
 	},
+	{
+		Name: "set character set",
+		SetUpScript: []string{
+			`set character set utf8`,
+		},
+		Query: "SELECT @@character_set_client, @@character_set_connection, @@character_set_results",
+		Expected: []sql.Row{
+			{"utf8", "utf8mb4", "utf8"},
+		},
+	},
+	{
+		Name: "set charset",
+		SetUpScript: []string{
+			`set charset utf8`,
+		},
+		Query: "SELECT @@character_set_client, @@character_set_connection, @@character_set_results",
+		Expected: []sql.Row{
+			{"utf8", "utf8mb4", "utf8"},
+		},
+	},
+	{
+		Name: "set charset quoted",
+		SetUpScript: []string{
+			`set charset 'utf8'`,
+		},
+		Query: "SELECT @@character_set_client, @@character_set_connection, @@character_set_results",
+		Expected: []sql.Row{
+			{"utf8", "utf8mb4", "utf8"},
+		},
+	},
 	{
 		Name: "set system variable to bareword",
 		SetUpScript: []string{

sql/parse/parse.go

@@ -346,6 +346,34 @@ func convertSet(ctx *sql.Context, n *sqlparser.Set) (sql.Node, error) {
 		})
 	}
 
+	// Special case: SET CHARACTER SET (CHARSET) expands to 3 different system variables. Although we do not support very
+	// many character sets, changing these variables should not have any effect currently as our character set support is
+	// mostly hardcoded to utf8mb4.
+	// See https://dev.mysql.com/doc/refman/5.7/en/set-character-set.html.
+	if isCharset(n.Exprs) {
+		csd, err := ctx.GetSessionVariable(ctx, "character_set_database")
+		if err != nil {
+			return nil, err
+		}
+
+		return convertSet(ctx, &sqlparser.Set{
+			Exprs: sqlparser.SetVarExprs{
+				&sqlparser.SetVarExpr{
+					Name: sqlparser.NewColName("character_set_client"),
+					Expr: n.Exprs[0].Expr,
+				},
+				&sqlparser.SetVarExpr{
+					Name: sqlparser.NewColName("character_set_results"),
+					Expr: n.Exprs[0].Expr,
+				},
+				&sqlparser.SetVarExpr{
+					Name: sqlparser.NewColName("character_set_connection"),
+					Expr: &sqlparser.SQLVal{Type: sqlparser.StrVal, Val: []byte(csd.(string))},
+				},
+			},
+		})
+	}
+
 	exprs, err := setExprsToExpressions(ctx, n.Exprs)
 	if err != nil {
 		return nil, err
@@ -362,6 +390,14 @@ func isSetNames(exprs sqlparser.SetVarExprs) bool {
 	return strings.ToLower(exprs[0].Name.String()) == "names"
 }
 
+func isCharset(exprs sqlparser.SetVarExprs) bool {
+	if len(exprs) != 1 {
+		return false
+	}
+
+	return strings.ToLower(exprs[0].Name.String()) == "charset"
+}
+
 func convertShow(ctx *sql.Context, s *sqlparser.Show, query string) (sql.Node, error) {
 	showType := strings.ToLower(s.Type)
 	switch showType {
@@ -572,6 +608,12 @@ func convertShow(ctx *sql.Context, s *sqlparser.Show, query string) (sql.Node, e
 		}
 
 		return infoSchemaSelect, nil
+	case sqlparser.KeywordString(sqlparser.STATUS):
+		if s.Scope == sqlparser.GlobalStr {
+			return plan.NewShowStatus(plan.ShowStatusModifier_Global), nil
+		}
+
+		return plan.NewShowStatus(plan.ShowStatusModifier_Session), nil
 	default:
 		unsupportedShow := fmt.Sprintf("SHOW %s", s.Type)
 		return nil, ErrUnsupportedFeature.New(unsupportedShow)

sql/plan/show_status.go

@@ -0,0 +1,75 @@
+// Copyright 2021 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package plan
+
+import (
+	"github.com/dolthub/vitess/go/sqltypes"
+
+	"github.com/dolthub/go-mysql-server/sql"
+)
+
+// ShowStatus implements the SHOW STATUS MySQL command.
+// TODO: This is just a stub implementation that returns an empty set. The actual functionality needs to be implemented
+// in the future.
+type ShowStatus struct {
+	modifier ShowStatusModifier
+}
+
+var _ sql.Node = (*ShowStatus)(nil)
+
+type ShowStatusModifier byte
+
+const (
+	ShowStatusModifier_Session ShowStatusModifier = iota
+	ShowStatusModifier_Global
+)
+
+// NewShowStatus returns a new ShowStatus reference.
+func NewShowStatus(modifier ShowStatusModifier) *ShowStatus {
+	return &ShowStatus{modifier: modifier}
+}
+
+// Resolved implements sql.Node interface.
+func (s *ShowStatus) Resolved() bool {
+	return true
+}
+
+// String implements sql.Node interface.
+func (s *ShowStatus) String() string {
+	return "SHOW STATUS"
+}
+
+// Schema implements sql.Node interface.
+func (s *ShowStatus) Schema() sql.Schema {
+	return sql.Schema{
+		{Name: "Variable_name", Type: sql.MustCreateStringWithDefaults(sqltypes.VarChar, 64), Default: nil, Nullable: false},
+		{Name: "Value", Type: sql.MustCreateStringWithDefaults(sqltypes.VarChar, 2048), Default: nil, Nullable: false},
+	}
+}
+
+// Children implements sql.Node interface.
+func (s *ShowStatus) Children() []sql.Node {
+	return nil
+}
+
+// RowIter implements sql.Node interface.
+func (s *ShowStatus) RowIter(ctx *sql.Context, row sql.Row) (sql.RowIter, error) {
+	return sql.RowsToRowIter(), nil
+}
+
+// WithChildren implements sql.Node interface.
+func (s *ShowStatus) WithChildren(node ...sql.Node) (sql.Node, error) {
+	return NewShowStatus(s.modifier), nil
+}