Question

我需要一些关于我正在尝试构建的MySQL查询的帮助。

这是我的表：

+----+-----------+---------+-----------+---------+------------+-----------+
| id |  fruit    | color   |  shape    | country |    vit     |   city    |
+----+-----------+---------+-----------+---------+------------+-----------+
| id |  Apple    | red     | spherical | UK      |     A      | London    |
| id |  Orange   | orange  | circular  | USA     |     C      | New York  |
| id |  Apple    | green   | multiple  | Mexico  |     C      | Cancun    |
| id |  Apple    | red     | spherical | Canada  |     B      | Ottawa    |
+----+-----------+---------+-----------+---------+------------+-----------+

现在我想使用一个查询来执行多个SELECT查询，如下所示：

SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit = "A" AND city = "London";
SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit = "B" AND city != "London;
SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit != "A" AND vit != "B" AND city != "London";

结果表将是：

+----+-----------+---------+-----------+---------+------------+-----------+
| id |  fruit    | color   |  shape    | country |    vit     |   city    |
+----+-----------+---------+-----------+---------+------------+-----------+
| id |  Apple    | red     | spherical | UK      |     A      | London    |
| id |  Apple    | green   | multiple  | Mexico  |     C      | Cancun    |
| id |  Apple    | red     | spherical | Canada  |     B      | Ottawa    |
+----+-----------+---------+-----------+---------+------------+-----------+

为了使所有这一切都有意义，我需要在三个条件下首先SELECT限制Apple的所有结果。然后，我需要使用第二个SELECT获取Apple的所有结果，但这次仅限制两个条件并排除第一个SELECT的结果，依此类推。

知道怎么做到这一点？我尝试了几个不同的查询，包括UNION，但不知何故无法显示我需要的结果。

Answer 1

使用select union而不是

SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit = "A" AND city = "London"
union
SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit = "B" AND city != "London
union
SELECT * from tbl_fruits WHERE fruit = "Apple" AND vit NOT IN ( "A" , "B" ) AND city != "London";

Answer 2

我错过了什么或OR还不够吗？

SELECT * 
FROM tbl_fruits 
WHERE (fruit = "Apple" AND vit = "A" AND city = "London")
   OR (fruit = "Apple" AND vit = "B" AND city != "London)
   OR (fruit = "Apple" AND vit != "A" AND vit != "B" AND city != "London")
;

可以重构为......

SELECT * 
FROM tbl_fruits 
WHERE fruit = "Apple" 
   AND (    (vit = "A" AND city = "London")
         OR (vit = "B" AND city != "London)
         OR (vit != "A" AND vit != "B" AND city != "London")
       )
;

...非常确定所有这些vit，城市组合的标准也可以缩小。

此外，UNION应该对您有用，并且可能更快，因为在使用OR时，MySQL几乎完全忽略了索引。

编辑：你可以得到第一个＆＃34;在上述查询中有六个ORDER BY和LIMIT 6，例如：

ORDER BY (fruit = "Apple" AND vit = "A" AND city = "London") DESC
   , (fruit = "Apple" AND vit = "B" AND city != "London) DESC
   , (fruit = "Apple" AND vit != "A" AND vit != "B" AND city != "London") DESC
LIMIT 6

...由于单个查询没有顺序，如果第一个条件产生的结果超过六个，则返回的六个可能会有所不同，但是将来自第一个查询/条件（当然，MySQL没有＆＃39;实际上保证查询将在连续执行时以相同的顺序返回结果。）

MySQL多个SELECT查询在同一个表上使用不同的WHERE子句

2 个答案: