MySQL prepare語句的SQL語法

MySQL prepare語法：

PREPARE statement_name FROM preparable_SQL_statement; /*定義*/

EXECUTE statement_name [USING @var_name [, @var_name] ...]; /*執行預處理語句*/

{DEALLOCATE | DROP} PREPARE statement_name /*刪除定義*/ ;

PREPARE語句用於預備一個語句，並指定名稱statement_name，之後引用該語句。語句名稱對大小寫不敏感。preparable_stmt能夠是一個文字字符串，也能夠是一個包含了語句文本的用戶變量。該文本必須表現爲一個單一的SQL語句，而不是多個語句。在這語句裏，‘?’字符能夠被用於標識參數，當執行時，以指示數據值綁定到查詢後。‘?’字符不該加引號，即便你想要把它們與字符串值結合在一塊兒。參數標記只能用於數據值應該出現的地方，而不是SQL關鍵字，標識符，等等。

若是預語句已經存在，則在新的預語句被定義前，它會被隱含地刪掉。

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)