DROP PLACEMENT POLICY
DROP PLACEMENT POLICY 用于删除已创建的放置策略。
语法图
- DropPolicyStmt
- PolicyName
DropPolicyStmt ::=
"DROP" "PLACEMENT" "POLICY" IfExists PolicyName
PolicyName ::=
Identifier
示例
删除放置规则时，确保该策略未被任何表或分区引用，否则会删除失败。
CREATE PLACEMENT POLICY p1 FOLLOWERS=4;
CREATE TABLE t1 (a INT PRIMARY KEY) PLACEMENT POLICY=p1;
DROP PLACEMENT POLICY p1; -- 该语句执行失败，因为放置规则 p1 被引用。
-- 查看引用放置规则的表和分区。
SELECT table_schema, table_name FROM information_schema.tables WHERE tidb_placement_policy_name='p1';
SELECT table_schema, table_name FROM information_schema.partitions WHERE tidb_placement_policy_name='p1';
ALTER TABLE t1 PLACEMENT POLICY=default; -- 移除表 t1 上的默认放置规则。
DROP PLACEMENT POLICY p1; -- 执行成功。
Query OK, 0 rows affected (0.10 sec)
Query OK, 0 rows affected (0.11 sec)
ERROR 8241 (HY000): Placement policy 'p1' is still in use
+--------------+------------+
| table_schema | table_name |
+--------------+------------+
| test | t1 |
+--------------+------------+
1 row in set (0.00 sec)
Empty set (0.01 sec)
Query OK, 0 rows affected (0.08 sec)
Query OK, 0 rows affected (0.21 sec)
MySQL 兼容性
该语句是 TiDB 对 MySQL 语法的扩展。