[parser] parser: support drop placement policy (pingcap#1295)

parser/ast/ddl.go

@@ -36,6 +36,7 @@ var (
 	_ DDLNode = &DropIndexStmt{}
 	_ DDLNode = &DropTableStmt{}
 	_ DDLNode = &DropSequenceStmt{}
+	_ DDLNode = &DropPlacementPolicyStmt{}
 	_ DDLNode = &RenameTableStmt{}
 	_ DDLNode = &TruncateTableStmt{}
 	_ DDLNode = &RepairTableStmt{}
@@ -1163,6 +1164,33 @@ func (n *DropTableStmt) Accept(v Visitor) (Node, bool) {
 	return v.Leave(n)
 }
 
+// DropPlacementPolicyStmt is a statement to drop a Policy.
+type DropPlacementPolicyStmt struct {
+	ddlNode
+
+	IfExists   bool
+	PolicyName model.CIStr
+}
+
+// Restore implements Restore interface.
+func (n *DropPlacementPolicyStmt) Restore(ctx *format.RestoreCtx) error {
+	ctx.WriteKeyWord("DROP PLACEMENT POLICY ")
+	if n.IfExists {
+		ctx.WriteKeyWord("IF EXISTS ")
+	}
+	ctx.WriteName(n.PolicyName.O)
+	return nil
+}
+
+func (n *DropPlacementPolicyStmt) Accept(v Visitor) (Node, bool) {
+	newNode, skipChildren := v.Enter(n)
+	if skipChildren {
+		return v.Leave(newNode)
+	}
+	n = newNode.(*DropPlacementPolicyStmt)
+	return v.Leave(n)
+}
+
 // DropSequenceStmt is a statement to drop a Sequence.
 type DropSequenceStmt struct {
 	ddlNode