query_expression_body EXCEPT [ALL | DISTINCT] query_expression_body
    [EXCEPT [ALL | DISTINCT] query_expression_body]
    [...]

query_expression_body:
    See Section 15.2.14, “Set Operations with UNION, INTERSECT, and EXCEPT”

EXCEPT 将第一个查询块的结果限制为第二个查询块中找不到的行。与UNION和INTERSECT一样，两个查询块都可以使用SELECT、TABLE或VALUES。使用表a、b和c（见第15.2.8节，“INTERSECT Clause”）的示例如下：

mysql> TABLE a EXCEPT TABLE b;
+------+------+
| m    | n    |
+------+------+
|    2 |    3 |
+------+------+
1 row in set (0.00 sec)

mysql> TABLE a EXCEPT TABLE c;
+------+------+
| m    | n    |
+------+------+
|    1 |    2 |
|    2 |    3 |
+------+------+
2 rows in set (0.00 sec)

mysql> TABLE b EXCEPT TABLE c;
+------+------+
| m    | n    |
+------+------+
|    1 |    2 |
+------+------+
1 row in set (0.00 sec)

与UNION和INTERSECT一样，如果不指定DISTINCT或ALL，默认为DISTINCT。

DISTINCT 删除两个关系中找到的重复项，如下所示：

mysql> TABLE c EXCEPT DISTINCT TABLE a;
+------+------+
| m    | n    |
+------+------+
|    1 |    3 |
+------+------+
1 row in set (0.00 sec)

mysql> TABLE c EXCEPT ALL TABLE a;
+------+------+
| m    | n    |
+------+------+
|    1 |    3 |
|    1 |    3 |
+------+------+
2 rows in set (0.00 sec)

(第一个语句等同于TABLE c EXCEPT TABLE a。)

与UNION或INTERSECT不同，EXCEPT不是可交换的—that is，结果取决于操作数的顺序，如下所示：

mysql> TABLE a EXCEPT TABLE c;
+------+------+
| m    | n    |
+------+------+
|    1 |    2 |
|    2 |    3 |
+------+------+
2 rows in set (0.00 sec)

mysql> TABLE c EXCEPT TABLE a;
+------+------+
| m    | n    |
+------+------+
|    1 |    3 |
+------+------+
1 row in set (0.00 sec)

与UNION一样，需要比较的结果集必须具有相同的列数。结果集列类型也像UNION一样确定。