planner: support subquery in SHOW statement

executor/builder.go

@@ -576,14 +576,7 @@ func (b *executorBuilder) buildShow(v *plannercore.Show) Executor {
 			b.err = err
 		}
 	}
-	if len(v.Conditions) == 0 {
-		return e
-	}
-	sel := &SelectionExec{
-		baseExecutor: newBaseExecutor(b.ctx, v.Schema(), v.ExplainID(), e),
-		filters:      v.Conditions,
-	}
-	return sel
+	return e
 }
 
 func (b *executorBuilder) buildSimple(v *plannercore.Simple) Executor {

planner/core/common_plans.go

@@ -357,7 +357,7 @@ type Deallocate struct {
 
 // Show represents a show plan.
 type Show struct {
-	baseSchemaProducer
+	physicalSchemaProducer
 
 	Tp          ast.ShowStmtType // Databases/Tables/Columns/....
 	DBName      string
@@ -370,8 +370,6 @@ type Show struct {
 	Roles       []*auth.RoleIdentity // Used for show grants.
 	IfNotExists bool                 // Used for `show create database if not exists`
 
-	Conditions []expression.Expression
-
 	GlobalScope bool // Used by show variables
 }
 

planner/core/find_best_task.go

@@ -69,7 +69,10 @@ func (p *LogicalTableDual) findBestTask(prop *property.PhysicalProperty) (task,
 	if !prop.IsEmpty() {
 		return invalidTask, nil
 	}
-	dual := PhysicalTableDual{RowCount: p.RowCount}.Init(p.ctx, p.stats)
+	dual := PhysicalTableDual{
+		RowCount:    p.RowCount,
+		placeHolder: p.placeHolder,
+	}.Init(p.ctx, p.stats)
 	dual.SetSchema(p.schema)
 	return &rootTask{p: dual}, nil
 }

planner/core/initialize.go

@@ -267,7 +267,9 @@ func (p Insert) Init(ctx sessionctx.Context) *Insert {
 
 // Init initializes Show.
 func (p Show) Init(ctx sessionctx.Context) *Show {
-	p.basePlan = newBasePlan(ctx, TypeShow)
+	p.basePhysicalPlan = newBasePhysicalPlan(ctx, TypeShow, &p)
+	// Just use pseudo stats to avoid panic.
+	p.stats = &property.StatsInfo{RowCount: 1}
 	return &p
 }
 

planner/core/integration_test.go

@@ -0,0 +1,61 @@
+// Copyright 2019 PingCAP, 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package core_test
+
+import (
+	. "github.com/pingcap/check"
+	"github.com/pingcap/tidb/util/testkit"
+)
+
+var _ = Suite(&testIntegrationSuite{})
+
+type testIntegrationSuite struct {
+}
+
+func (s *testIntegrationSuite) TestShowSubquery(c *C) {
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	tk := testkit.NewTestKit(c, store)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a varchar(10), b int, c int)")
+	tk.MustQuery("show columns from t where true").Check(testkit.Rows(
+		"a varchar(10) YES  <nil> ",
+		"b int(11) YES  <nil> ",
+		"c int(11) YES  <nil> ",
+	))
+	tk.MustQuery("show columns from t where field = 'b'").Check(testkit.Rows(
+		"b int(11) YES  <nil> ",
+	))
+	tk.MustQuery("show columns from t where field in (select 'b')").Check(testkit.Rows(
+		"b int(11) YES  <nil> ",
+	))
+	tk.MustQuery("show columns from t where field in (select 'b') and true").Check(testkit.Rows(
+		"b int(11) YES  <nil> ",
+	))
+	tk.MustQuery("show columns from t where field in (select 'b') and false").Check(testkit.Rows())
+	tk.MustExec("insert into t values('c', 0, 0)")
+	tk.MustQuery("show columns from t where field < all (select a from t)").Check(testkit.Rows(
+		"a varchar(10) YES  <nil> ",
+		"b int(11) YES  <nil> ",
+	))
+	tk.MustExec("insert into t values('b', 0, 0)")
+	tk.MustQuery("show columns from t where field < all (select a from t)").Check(testkit.Rows(
+		"a varchar(10) YES  <nil> ",
+	))
+}

planner/core/logical_plan_test.go

@@ -829,7 +829,7 @@ func (s *testPlanSuite) TestPlanBuilder(c *C) {
 		},
 		{
 			sql:  "show columns from t where `Key` = 'pri' like 't*'",
-			plan: "Show([eq(cast(key), 0)])",
+			plan: "Show->Sel([eq(cast(key), 0)])",
 		},
 		{
 			sql:  "do sleep(5)",

planner/core/logical_plans.go

@@ -308,6 +308,10 @@ type LogicalTableDual struct {
 	logicalSchemaProducer
 
 	RowCount int
+	// placeHolder indicates if this dual plan is a place holder in query optimization
+	// for data sources like `Show`, if true, the dual plan would be substituted by
+	// `Show` in the final plan.
+	placeHolder bool
 }
 
 // LogicalUnionScan is only used in non read-only txn.

planner/core/physical_plans.go

@@ -378,6 +378,10 @@ type PhysicalTableDual struct {
 	physicalSchemaProducer
 
 	RowCount int
+	// placeHolder indicates if this dual plan is a place holder in query optimization
+	// for data sources like `Show`, if true, the dual plan would be substituted by
+	// `Show` in the final plan.
+	placeHolder bool
 }
 
 // PhysicalWindow is the physical operator of window function.

planner/core/plan.go

@@ -141,6 +141,9 @@ type PhysicalPlan interface {
 	// SetChildren sets the children for the plan.
 	SetChildren(...PhysicalPlan)
 
+	// SetChild sets the ith child for the plan.
+	SetChild(i int, child PhysicalPlan)
+
 	// ResolveIndices resolves the indices for columns. After doing this, the columns can evaluate the rows by their indices.
 	ResolveIndices() error
 }
@@ -296,6 +299,11 @@ func (p *basePhysicalPlan) SetChildren(children ...PhysicalPlan) {
 	p.children = children
 }
 
+// SetChild implements PhysicalPlan SetChild interface.
+func (p *basePhysicalPlan) SetChild(i int, child PhysicalPlan) {
+	p.children[i] = child
+}
+
 func (p *basePlan) context() sessionctx.Context {
 	return p.ctx
 }

planner/core/planbuilder.go

@@ -1121,35 +1121,58 @@ func (b *PlanBuilder) buildShow(show *ast.ShowStmt) (Plan, error) {
 	for _, col := range p.schema.Columns {
 		col.UniqueID = b.ctx.GetSessionVars().AllocPlanColumnID()
 	}
-	mockTablePlan := LogicalTableDual{}.Init(b.ctx)
+	mockTablePlan := LogicalTableDual{placeHolder: true}.Init(b.ctx)
 	mockTablePlan.SetSchema(p.schema)
+	var err error
+	var np LogicalPlan
+	np = mockTablePlan
 	if show.Pattern != nil {
 		show.Pattern.Expr = &ast.ColumnNameExpr{
 			Name: &ast.ColumnName{Name: p.Schema().Columns[0].ColName},
 		}
-		expr, _, err := b.rewrite(show.Pattern, mockTablePlan, nil, false)
+		np, err = b.buildSelection(np, show.Pattern, nil)
 		if err != nil {
 			return nil, err
 		}
-		p.Conditions = append(p.Conditions, expr)
 	}
 	if show.Where != nil {
-		conds := splitWhere(show.Where)
-		for _, cond := range conds {
-			expr, _, err := b.rewrite(cond, mockTablePlan, nil, false)
-			if err != nil {
-				return nil, err
-			}
-			p.Conditions = append(p.Conditions, expr)
+		np, err = b.buildSelection(np, show.Where, nil)
+		if err != nil {
+			return nil, err
 		}
-		err := p.ResolveIndices()
+	}
+	if np != mockTablePlan {
+		fieldsLen := len(mockTablePlan.schema.Columns)
+		proj := LogicalProjection{Exprs: make([]expression.Expression, 0, fieldsLen)}.Init(b.ctx)
+		schema := expression.NewSchema(make([]*expression.Column, 0, fieldsLen)...)
+		for _, col := range mockTablePlan.schema.Columns {
+			proj.Exprs = append(proj.Exprs, col)
+			newCol := col.Clone().(*expression.Column)
+			newCol.UniqueID = b.ctx.GetSessionVars().AllocPlanColumnID()
+			schema.Append(newCol)
+		}
+		proj.SetSchema(schema)
+		proj.SetChildren(np)
+		physical, err := DoOptimize(b.optFlag|flagEliminateProjection, proj)
 		if err != nil {
 			return nil, err
 		}
+		return substitutePlaceHolderDual(physical, p), nil
 	}
 	return p, nil
 }
 
+func substitutePlaceHolderDual(src PhysicalPlan, dst PhysicalPlan) PhysicalPlan {
+	if dual, ok := src.(*PhysicalTableDual); ok && dual.placeHolder {
+		return dst
+	}
+	for i, child := range src.Children() {
+		newChild := substitutePlaceHolderDual(child, dst)
+		src.SetChild(i, newChild)
+	}
+	return src
+}
+
 func (b *PlanBuilder) buildSimple(node ast.StmtNode) (Plan, error) {
 	p := &Simple{Statement: node}
 

planner/core/point_get_plan.go

@@ -124,6 +124,9 @@ func (p *PointGetPlan) Children() []PhysicalPlan {
 // SetChildren sets the children for the plan.
 func (p *PointGetPlan) SetChildren(...PhysicalPlan) {}
 
+// SetChild sets a specific child for the plan.
+func (p *PointGetPlan) SetChild(i int, child PhysicalPlan) {}
+
 // ResolveIndices resolves the indices for columns. After doing this, the columns can evaluate the rows by their indices.
 func (p *PointGetPlan) ResolveIndices() error {
 	return nil

planner/core/resolve_indices.go

@@ -480,17 +480,6 @@ func (p *Insert) ResolveIndices() (err error) {
 	return
 }
 
-// ResolveIndices implements Plan interface.
-func (p *Show) ResolveIndices() (err error) {
-	for i, expr := range p.Conditions {
-		p.Conditions[i], err = expr.ResolveIndices(p.schema)
-		if err != nil {
-			return err
-		}
-	}
-	return err
-}
-
 func (p *physicalSchemaProducer) ResolveIndices() (err error) {
 	err = p.basePhysicalPlan.ResolveIndices()
 	if err != nil {

planner/core/stringer.go

@@ -114,11 +114,7 @@ func toString(in Plan, strs []string, idxs []int) ([]string, []int) {
 	case *ShowDDL:
 		str = "ShowDDL"
 	case *Show:
-		if len(x.Conditions) == 0 {
-			str = "Show"
-		} else {
-			str = fmt.Sprintf("Show(%s)", x.Conditions)
-		}
+		str = "Show"
 	case *LogicalSort, *PhysicalSort:
 		str = "Sort"
 	case *LogicalJoin: