DROP PLACEMENT POLICY

DROP PLACEMENT POLICY 用于删除已创建的放置策略。

语法图

DropPolicyStmt

DROP PLACEMENT POLICY - 图1

PolicyName

DROP PLACEMENT POLICY - 图2

1. DropPolicyStmt ::=
2. "DROP" "PLACEMENT" "POLICY" IfExists PolicyName

4. PolicyName ::=
5. 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。

1. CREATE PLACEMENT POLICY p1 FOLLOWERS=4;
2. CREATE TABLE t1 (a INT PRIMARY KEY) PLACEMENT POLICY=p1;
3. DROP PLACEMENT POLICY p1;  -- 该语句执行失败，因为放置规则 p1 被引用。

5. -- 查看引用放置规则的表和分区。
6. SELECT table_schema, table_name FROM information_schema.tables WHERE tidb_placement_policy_name='p1';
7. SELECT table_schema, table_name FROM information_schema.partitions WHERE tidb_placement_policy_name='p1';

9. ALTER TABLE t1 PLACEMENT POLICY=default;  -- 移除表 t1 上的默认放置规则。
10. DROP PLACEMENT POLICY p1;  -- 执行成功。

1. Query OK, 0 rows affected (0.10 sec)

3. Query OK, 0 rows affected (0.11 sec)

5. ERROR 8241 (HY000): Placement policy 'p1' is still in use

7. +--------------+------------+
8. | table_schema | table_name |
9. +--------------+------------+
10. | test         | t1         |
11. +--------------+------------+
12. 1 row in set (0.00 sec)

14. Empty set (0.01 sec)

16. Query OK, 0 rows affected (0.08 sec)

18. Query OK, 0 rows affected (0.21 sec)

MySQL 兼容性

该语句是 TiDB 对 MySQL 语法的扩展。

另请参阅