*: add pushdown for ShowStmt and implement for show columns (#31742) (#…

…33342)

close #29910

executor/builder.go

@@ -764,6 +764,7 @@ func (b *executorBuilder) buildShow(v *plannercore.PhysicalShow) Executor {
 		IfNotExists:  v.IfNotExists,
 		GlobalScope:  v.GlobalScope,
 		Extended:     v.Extended,
+		Extractor:    v.Extractor,
 	}
 	if e.Tp == ast.ShowMasterStatus {
 		// show master status need start ts.

executor/show.go

@@ -20,6 +20,7 @@ import (
 	gjson "encoding/json"
 	"fmt"
 	"reflect"
+	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -84,6 +85,7 @@ type ShowExec struct {
 	Flag      int                  // Some flag parsed from sql, such as FULL.
 	Roles     []*auth.RoleIdentity // Used for show grants.
 	User      *auth.UserIdentity   // Used by show grants, show create user.
+	Extractor plannercore.ShowPredicateExtractor
 
 	is infoschema.InfoSchema
 
@@ -514,10 +516,23 @@ func (e *ShowExec) fetchShowTableStatus(ctx context.Context) error {
 
 func (e *ShowExec) fetchShowColumns(ctx context.Context) error {
 	tb, err := e.getTable()
-
 	if err != nil {
 		return errors.Trace(err)
 	}
+	var (
+		fieldPatternsRegexp *regexp.Regexp
+		FieldFilterEnable   bool
+		fieldFilter         string
+	)
+	if e.Extractor != nil {
+		extractor := (e.Extractor).(*plannercore.ShowColumnsTableExtractor)
+		if extractor.FieldPatterns != "" {
+			fieldPatternsRegexp = regexp.MustCompile(extractor.FieldPatterns)
+		}
+		FieldFilterEnable = extractor.Field != ""
+		fieldFilter = extractor.Field
+	}
+
 	checker := privilege.GetPrivilegeManager(e.ctx)
 	activeRoles := e.ctx.GetSessionVars().ActiveRoles
 	if checker != nil && e.ctx.GetSessionVars().User != nil && !checker.RequestVerification(activeRoles, e.DBName.O, tb.Meta().Name.O, "", mysql.InsertPriv|mysql.SelectPriv|mysql.UpdatePriv|mysql.ReferencesPriv) {
@@ -536,10 +551,11 @@ func (e *ShowExec) fetchShowColumns(ctx context.Context) error {
 		return err
 	}
 	for _, col := range cols {
-		if e.Column != nil && e.Column.Name.L != col.Name.L {
+		if FieldFilterEnable && col.Name.L != fieldFilter {
+			continue
+		} else if fieldPatternsRegexp != nil && !fieldPatternsRegexp.MatchString(col.Name.L) {
 			continue
 		}
-
 		desc := table.NewColDesc(col)
 		var columnDefault interface{}
 		if desc.DefaultValue != nil {

planner/cascades/implementation_rules.go

@@ -242,12 +242,14 @@ func (r *ImplShow) Match(expr *memo.GroupExpr, prop *property.PhysicalProperty)
 func (r *ImplShow) OnImplement(expr *memo.GroupExpr, reqProp *property.PhysicalProperty) ([]memo.Implementation, error) {
 	logicProp := expr.Group.Prop
 	show := expr.ExprNode.(*plannercore.LogicalShow)
-
 	// TODO(zz-jason): unifying LogicalShow and PhysicalShow to a single
 	// struct. So that we don't need to create a new PhysicalShow object, which
 	// can help us to reduce the gc pressure of golang runtime and improve the
 	// overall performance.
-	showPhys := plannercore.PhysicalShow{ShowContents: show.ShowContents}.Init(show.SCtx())
+	showPhys := plannercore.PhysicalShow{
+		ShowContents: show.ShowContents,
+		Extractor:    show.Extractor,
+	}.Init(show.SCtx())
 	showPhys.SetSchema(logicProp.Schema)
 	return []memo.Implementation{impl.NewShowImpl(showPhys)}, nil
 }

planner/core/find_best_task.go

@@ -155,7 +155,7 @@ func (p *LogicalShow) findBestTask(prop *property.PhysicalProperty, planCounter
 	if !prop.IsEmpty() || planCounter.Empty() {
 		return invalidTask, 0, nil
 	}
-	pShow := PhysicalShow{ShowContents: p.ShowContents}.Init(p.ctx)
+	pShow := PhysicalShow{ShowContents: p.ShowContents, Extractor: p.Extractor}.Init(p.ctx)
 	pShow.SetSchema(p.schema)
 	planCounter.Dec(1)
 	return &rootTask{p: pShow}, 1, nil

planner/core/logical_plans.go

@@ -1261,6 +1261,8 @@ type ShowContents struct {
 type LogicalShow struct {
 	logicalSchemaProducer
 	ShowContents
+
+	Extractor ShowPredicateExtractor
 }
 
 // LogicalShowDDLJobs is for showing DDL job list.