MySQL中预处理语句prepare、execute与deallocate的使用教程

前言

MySQL官方将prepare、execute、deallocate统称为PREPARE STATEMENT，我习惯称其为【预处理语句】，其用法十分简单，下面话不多说，来一起看看详细的介绍吧。

示例代码

									PREPARE stmt_name FROM preparable_stmt

									EXECUTE stmt_name

									 [USING @var_name [, @var_name] ...] -

									{DEALLOCATE | DROP} PREPARE stmt_name

举个栗子：

									mysql> PREPARE pr1 FROM 'SELECT ?+?';

									Query OK, 0 rows affected (0.01 sec)

									Statement prepared

									mysql> SET @a=1, @b=10 ;

									Query OK, 0 rows affected (0.00 sec)

									mysql> EXECUTE pr1 USING @a, @b;

									+------+

									| ?+? |

									+------+

									| 11 |

									+------+

									1 row in set (0.00 sec)

									mysql> EXECUTE pr1 USING 1, 2; -- 只能使用用户变量传递。

									ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the 

									right syntax to use near '1, 2' at line 1

									mysql> DEALLOCATE PREPARE pr1;

									Query OK, 0 rows affected (0.00 sec)

使用PAREPARE STATEMENT可以减少每次执行SQL的语法分析，比如用于执行带有WHERE条件的SELECT和DELETE，或者UPDATE，或者INSERT，只需要每次修改变量值即可。

同样可以防止SQL注入，参数值可以包含转义符和定界符。

适用在应用程序中，或者SQL脚本中均可。

更多用法：

同样PREPARE ... FROM可以直接接用户变量：

									mysql> CREATE TABLE a (a int);

									Query OK, 0 rows affected (0.26 sec)

									mysql> INSERT INTO a SELECT 1;

									Query OK, 1 row affected (0.04 sec)

									Records: 1 Duplicates: 0 Warnings: 0

									mysql> INSERT INTO a SELECT 2;

									Query OK, 1 row affected (0.04 sec)

									Records: 1 Duplicates: 0 Warnings: 0

									mysql> INSERT INTO a SELECT 3;

									Query OK, 1 row affected (0.04 sec)

									Records: 1 Duplicates: 0 Warnings: 0

									mysql> SET @select_test = CONCAT('SELECT * FROM ', @table_name);

									Query OK, 0 rows affected (0.00 sec)

									mysql> SET @table_name = 'a';

									Query OK, 0 rows affected (0.00 sec)

									mysql> PREPARE pr2 FROM @select_test;

									Query OK, 0 rows affected (0.00 sec)

									Statement prepared

									mysql> EXECUTE pr2 ;

									+------+

									| a |

									+------+

									| 1 |

									| 2 |

									| 3 |

									+------+

									3 rows in set (0.00 sec)

									mysql> DROP PREPARE pr2; -- 此处DROP可以替代DEALLOCATE

									Query OK, 0 rows affected (0.00 sec)