[ISSUE arana-db#93] Feat show var (arana-db#154)

* feat: none

* feat: support show var

* feat: support show variables

* style: 移除无效代码

* feat: 逻辑修改

* fix: 修复PR中的comment

.gitignore

@@ -21,4 +21,7 @@ vendor/
 /docker/data/
 /docker/mysqld/
 /dist
-/default.etcd
+/default.etcd
+
+.codecc
+.vscode

pkg/executor/redirect.go

@@ -230,7 +230,18 @@ func (executor *RedirectExecutor) ExecutorComQuery(ctx *proto.Context) (proto.Re
 			}
 		}
 	case *ast.ShowStmt:
-		if !schemaless || stmt.Tp == ast.ShowDatabases { // only SHOW DATABASES is allowed in schemaless mode
+		allowSchemaless := func(stmt *ast.ShowStmt) bool {
+			if stmt.Tp == ast.ShowDatabases {
+				return true
+			}
+			if stmt.Tp == ast.ShowVariables {
+				return true
+			}
+
+			return false
+		}
+
+		if !schemaless || allowSchemaless(stmt) { // only SHOW DATABASES is allowed in schemaless mode
 			res, warn, err = rt.Execute(ctx)
 		} else {
 			err = errNoDatabaseSelected

pkg/runtime/ast/ast.go

@@ -405,6 +405,16 @@ func (cc *convCtx) convShowStmt(node *ast.ShowStmt) Statement {
 			ret.like.Valid, ret.like.String = true, like
 		}
 		return ret
+	case ast.ShowVariables:
+		ret := &ShowVariables{}
+		if node.Full {
+			ret.flag |= scFlagFull
+		}
+		if like, ok := toLike(node); ok {
+			ret.like.Valid = true
+			ret.like.String = like
+		}
+		return ret
 	default:
 		panic(fmt.Sprintf("unimplement: show type %v!", node.Tp))
 	}

pkg/runtime/ast/drop_table.go

@@ -20,6 +20,7 @@ package ast
 import (
 	"strings"
 )
+
 import (
 	"github.com/pkg/errors"
 )

pkg/runtime/ast/show.go

@@ -306,3 +306,41 @@ func (sh *ShowColumns) TableFormat() string {
 	}
 	return "FROM"
 }
+
+type ShowVariables struct {
+	flag showColumnsFlag
+	like sql.NullString
+}
+
+func (s *ShowVariables) Validate() error {
+	return nil
+}
+
+func (s *ShowVariables) Restore(flag RestoreFlag, sb *strings.Builder, args *[]int) error {
+	sb.WriteString("SHOW VARIABLES ")
+
+	if s.like.Valid {
+		sb.WriteString(" LIKE ")
+
+		sb.WriteByte('\'')
+		sb.WriteString(s.like.String)
+		sb.WriteByte('\'')
+	}
+
+	return nil
+}
+
+func (s *ShowVariables) Like() (string, bool) {
+	if s.like.Valid {
+		return s.like.String, true
+	}
+	return "", false
+}
+
+func (s *ShowVariables) CntParams() int {
+	return 0
+}
+
+func (s *ShowVariables) Mode() SQLType {
+	return Squery
+}

pkg/runtime/optimize/optimizer.go

@@ -115,6 +115,8 @@ func (o optimizer) doOptimize(ctx context.Context, conn proto.VConn, stmt rast.S
 		return o.optimizeTruncate(ctx, t, args)
 	case *rast.DropTableStatement:
 		return o.optimizeDropTable(ctx, t, args)
+	case *rast.ShowVariables:
+		return o.optimizeShowVariables(ctx, t, args)
 	}
 
 	//TODO implement all statements
@@ -554,6 +556,12 @@ func (o optimizer) optimizeTruncate(ctx context.Context, stmt *rast.TruncateStat
 	return ret, nil
 }
 
+func (o optimizer) optimizeShowVariables(ctx context.Context, stmt *rast.ShowVariables, args []interface{}) (proto.Plan, error) {
+	ret := plan.NewShowVariablesPlan(stmt)
+	ret.BindArgs(args)
+	return ret, nil
+}
+
 func (o optimizer) computeShards(ru *rule.Rule, table rast.TableName, where rast.ExpressionNode, args []interface{}) (rule.DatabaseTables, error) {
 	vt, ok := ru.VTable(table.Suffix())
 	if !ok {

pkg/runtime/plan/drop_table.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"strings"
 )
+
 import (
 	"github.com/arana-db/arana/pkg/mysql"
 	"github.com/arana-db/arana/pkg/proto"

pkg/runtime/plan/variables.go

@@ -0,0 +1,66 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 (
+	"context"
+	"strings"
+)
+
+import (
+	"github.com/pkg/errors"
+)
+
+import (
+	"github.com/arana-db/arana/pkg/proto"
+	"github.com/arana-db/arana/pkg/runtime/ast"
+)
+
+var _ proto.Plan = (*ShowVariablesPlan)(nil)
+
+type ShowVariablesPlan struct {
+	basePlan
+	stmt *ast.ShowVariables
+}
+
+func NewShowVariablesPlan(stmt *ast.ShowVariables) *ShowVariablesPlan {
+	return &ShowVariablesPlan{stmt: stmt}
+}
+
+func (s *ShowVariablesPlan) Type() proto.PlanType {
+	return proto.PlanTypeQuery
+}
+
+func (s *ShowVariablesPlan) ExecIn(ctx context.Context, vConn proto.VConn) (proto.Result, error) {
+
+	var (
+		sb   strings.Builder
+		args []int
+	)
+
+	if err := s.stmt.Restore(ast.RestoreDefault, &sb, &args); err != nil {
+		return nil, errors.Wrap(err, "failed to execute DELETE statement")
+	}
+
+	ret, err := vConn.Query(ctx, "", sb.String(), s.toArgs(args)...)
+	if err != nil {
+		return nil, err
+	}
+
+	return ret, nil
+}

test/integration_test.go

@@ -25,6 +25,7 @@ import (
 
 import (
 	_ "github.com/go-sql-driver/mysql" // register mysql
+
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/suite"
 )