MySQL存储过程变量前@的含义

　　在MySQL存储过程变量前加@符号代表会话变量，作用域是当前登陆的帐户，DECLARE申明的变量只在存储过程内部有效。

mysql> delimiter //
mysql> CREATE PROCEDURE pro2()
    -> BEGIN
    -> DECLARE d int;
    -> SELECT MAX(id) INTO d from php_coder;
    -> SET @dd=0;
    -> SELECT MAX(id) INTO @dd FROM php_coder;
    -> END;
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> call pro2();
    -> //
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT @dd;
    -> //
+------+
| @dd |
+------+
| 7    |
+------+
1 row in set (0.00 sec)

mysql> SELECT d//
ERROR 1054 (42S22): Unknown column 'd' in 'field list'