parser: support show placement ... syntax (#1292)

* parser: support `show placement ...` syntax

* Add parser.go

ast/dml.go

@@ -2528,6 +2528,10 @@ const (
 	ShowRestores
 	ShowImports
 	ShowCreateImport
+	ShowPlacement
+	ShowPlacementForDatabase
+	ShowPlacementForTable
+	ShowPlacementForPartition
 )
 
 const (
@@ -2551,6 +2555,7 @@ type ShowStmt struct {
 	Tp          ShowStmtType // Databases/Tables/Columns/....
 	DBName      string
 	Table       *TableName  // Used for showing columns.
+	Partition   model.CIStr // Used for showing partition.
 	Column      *ColumnName // Used for `desc table column`.
 	IndexName   model.CIStr
 	Flag        int // Some flag parsed from sql, such as FULL.
@@ -2738,6 +2743,21 @@ func (n *ShowStmt) Restore(ctx *format.RestoreCtx) error {
 	case ShowCreateImport:
 		ctx.WriteKeyWord("CREATE IMPORT ")
 		ctx.WriteName(n.DBName)
+	case ShowPlacementForDatabase:
+		ctx.WriteKeyWord("PLACEMENT FOR DATABASE ")
+		ctx.WriteName(n.DBName)
+	case ShowPlacementForTable:
+		ctx.WriteKeyWord("PLACEMENT FOR TABLE ")
+		if err := n.Table.Restore(ctx); err != nil {
+			return errors.Annotate(err, "An error occurred while resotre ShowStmt.Table")
+		}
+	case ShowPlacementForPartition:
+		ctx.WriteKeyWord("PLACEMENT FOR TABLE ")
+		if err := n.Table.Restore(ctx); err != nil {
+			return errors.Annotate(err, "An error occurred while resotre ShowStmt.Table")
+		}
+		ctx.WriteKeyWord(" PARTITION ")
+		ctx.WriteName(n.Partition.String())
 	// ShowTargetFilterable
 	default:
 		switch n.Tp {
@@ -2842,6 +2862,8 @@ func (n *ShowStmt) Restore(ctx *format.RestoreCtx) error {
 			ctx.WriteKeyWord("RESTORES")
 		case ShowImports:
 			ctx.WriteKeyWord("IMPORTS")
+		case ShowPlacement:
+			ctx.WriteKeyWord("PLACEMENT")
 		default:
 			return errors.New("Unknown ShowStmt type")
 		}