# DEALLOCATE
#### 功能描述
从数据库中删除一个预备语句。
#### 注意事项
使用DEALLOCATE可以手动释放通过PREPARE创建的预处理语句。如果未显式释放，预处理语句会在会话结束时自动清除。
#### 语法格式
```
DEALLOCATE [ PREPARE ] { name | ALL };
```
![](https://support.huaweicloud.com/distributed-ref-v10-gaussdb/figure/zh-cn_image_0000002793708097.png "点击放大")
#### 参数说明
- **PREPARE**
  可选，仅用于语法兼容性，实际执行时会被忽略。
  
- **name**
  将要删除的预备语句。
  
- **ALL**
  删除所有预备语句。
  
 
#### 示例
```
--查看现有预备语句。
gaussdb=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name | statement | parameter_types 
------+-----------+-----------------
(0 rows)
--创建q1,q2,q3，q4四个预备语句。
gaussdb=# PREPARE q1 AS SELECT 1 AS a;
PREPARE
gaussdb=# PREPARE q2 AS SELECT 1 AS a;
PREPARE
gaussdb=# PREPARE q3 AS SELECT 1 AS a;
PREPARE
gaussdb=# PREPARE q4 AS SELECT 1 AS a;
PREPARE
--再次查看现有预备语句。
gaussdb=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name |          statement           | parameter_types 
------+------------------------------+-----------------
 q1   | PREPARE q1 AS SELECT 1 AS a; | {}
 q4   | PREPARE q4 AS SELECT 1 AS a; | {}
 q3   | PREPARE q3 AS SELECT 1 AS a; | {}
 q2   | PREPARE q2 AS SELECT 1 AS a; | {}
(4 rows)
--删除q4预备语句并查看剩余预备语句。
gaussdb=# DEALLOCATE q4;
gaussdb=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name |          statement           | parameter_types 
------+------------------------------+-----------------
 q1   | PREPARE q1 AS SELECT 1 AS a; | {}
 q3   | PREPARE q3 AS SELECT 1 AS a; | {}
 q2   | PREPARE q2 AS SELECT 1 AS a; | {}
(3 rows）
--删除所有预备语句并查看剩余预备语句。
gaussdb=# DEALLOCATE ALL;
DEALLOCATE ALL
gaussdb=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name | statement | parameter_types 
------+-----------+-----------------
(0 rows)
```