MySQL prepare语句的SQL语法

MySQL prepare语法：

PREPARE statement_name FROM preparable_SQL_statement; /*定义*/

EXECUTE statement_name [USING @var_name [, @var_name] ...]; /*执行预处理语句*/

{DEALLOCATE | DROP} PREPARE statement_name /*删除定义*/ ;

PREPARE语句用于预备一个语句，并指定名称statement_name，以后引用该语句。语句名称对大小写不敏感。preparable_stmt可以是一个文字字符串，也可以是一个包含了语句文本的用户变量。该文本必须表现为一个单一的SQL语句，而不是多个语句。在这语句里，‘?’字符可以被用于标识参数，当执行时，以指示数据值绑定到查询后。‘?’字符不应加引号，即使你想要把它们与字符串值结合在一起。参数标记只能用于数据值应该出现的地方，而不是SQL关键字，标识符，等等。

如果预语句已经存在，则在新的预语句被定义前，它会被隐含地删掉。

例如：

mysql> prepare optimize_tables from "optimize table temp";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> execute optimize_tables;
+-----------+----------+----------+----------+
| Table     | Op       | Msg_type | Msg_text |
+-----------+----------+----------+----------+
| test.temp | optimize | status   | OK       | 
+-----------+----------+----------+----------+
1 row in set (0.37 sec)

mysql> deallocate prepare optimize_tables;
Query OK, 0 rows affected (0.00 sec)

--------------------------------------------------------------------------
mysql> prepare md5sum from 'select md5(?) AS md5sum';
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> set @a=111;
Query OK, 0 rows affected (0.00 sec)

mysql> set @b=222;
Query OK, 0 rows affected (0.00 sec)

mysql> execute md5sum using @a;
+----------------------------------+
| md5sum                           |
+----------------------------------+
| 698d51a19d8a121ce581499d7b701668 | 
+----------------------------------+
1 row in set (0.00 sec)

mysql> execute md5sum using @b;
+----------------------------------+
| md5sum                           |
+----------------------------------+
| bcbe3365e6ac95ea2c0343a2395834dd | 
+----------------------------------+
1 row in set (0.00 sec)

mysql> drop prepare md5sum;
Query OK, 0 rows affected (0.00 sec)

--------------------------------------------------------------------------------------

mysql> prepare update_table from "update users set password=password('aaa') where username='a'";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> execute update_table;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0

mysql> deallocate prepare update_table;
Query OK, 0 rows affected (0.00 sec)