MySQL语法错误

Question

我无法在 MySQL 中运行简单的脚本。我已将脚本缩减为一行。

DELIMITER $$
DECLARE varLocalityName VARCHAR(50);
$$
DELIMITER ;

错误是:

ERROR 1064 (42000) at line 2: 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 'DECLARE varLocalityName VARCHAR(50)' at line 1

$ mysql --version
mysql  Ver 14.14 Distrib 5.1.63, for debian-linux-gnu (x86_64) using readline 6.2

Answer 1

您的代码块没有定义声明变量的范围。如果在过程中，它们必须在 BEGIN 和 END 之间。没有它们，语句 DECLARE varLocalityName VARCHAR(50); 将成为要执行的无效语句。此语句等同于下面显示的语句:

mysql> select current_date();
+----------------+
| current_date() |
+----------------+
| 2012-10-22     |
+----------------+
1 row in set (0.00 sec)

mysql> declare varLocalityName varchar(50);
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 'declare varLocalityName varchar(50)' at line 1
mysql>

要么您应该声明不带关键字DECLARE 的 session 变量，要么遵循为存储过程定义的语法以使用作用域变量。

示例 1:使用 session 变量:

mysql> set @x = null;
Query OK, 0 rows affected (0.00 sec)
mysql> select @x;
+------+
| @x   |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

mysql> delimiter $$
mysql> select current_date() into @x;
    -> $$
Query OK, 1 row affected (0.02 sec)

mysql> select @x;
    -> $$
+------------+
| @x         |
+------------+
| 2012-10-22 |
+------------+
1 row in set (0.00 sec)

请注意，您可以在过程中设置/定义 session 变量，但不能DECLARE。

示例 2:使用过程范围变量:

mysql>
mysql> delimiter $$
mysql> create procedure some_x()
    ->    begin
    ->      declare varLocalityName varchar(50);
    ->
    ->      set @sessionDate = null;
    ->      select @sessionDate;
    ->      set @sessionDate = current_date();
    ->      select @sessionDate;
    ->
    ->      select varLocalityName;
    ->    end;
    -> $$
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;
mysql>
mysql> call some_x();
+--------------+
| @sessionDate |
+--------------+
| NULL         |
+--------------+
1 row in set (0.00 sec)

+--------------+
| @sessionDate |
+--------------+
| 2012-10-22   |
+--------------+
1 row in set (0.00 sec)

+-----------------+
| varLocalityName |
+-----------------+
| NULL            |
+-----------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> select @sessionDate;
+--------------+
| @sessionDate |
+--------------+
| 2012-10-22   |
+--------------+
1 row in set (0.00 sec)

mysql> select varLocalityName;
ERROR 1054 (42S22): Unknown column 'varLocalityName' in 'field list'
mysql>

另请参阅 Variables declaration and scope .