# DEALLOCATE
#### 功能描述
用于删除前面编写的预备语句。
#### 注意事项
如果用户没有明确删除一个预备语句，那么它将在会话结束的时候被删除。
#### 语法格式
```
{DEALLOCATE | DROP}  PREPARE name;
```
#### 参数说明
**name**
将要删除的预备语句。
#### 示例
```
--创建q1,q2,q3三个预备语句，先删除q1，再删除所有预备语句。
m_db=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name | statement | parameter_types 
------+-----------+-----------------
(0 rows)
m_db=# PREPARE q1 from  'SELECT 1 AS a';
PREPARE
m_db=# PREPARE q2 from 'SELECT 1 AS a';
PREPARE
m_db=# PREPARE q3 from 'SELECT 1 AS a';
PREPARE
m_db=# 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)
m_db=# DEALLOCATE PREPARE q1;
DEALLOCATE
m_db=# SELECT name, statement, parameter_types FROM pg_prepared_statements;
 name |          statement           | parameter_types 
------+------------------------------+-----------------
 q3   | PREPARE q3 AS SELECT 1 AS a; | {}
 q2   | PREPARE q2 AS SELECT 1 AS a; | {}
(2 rows)
```