MySQL在同一张表上具有不同WHERE子句的多个SELECT查询

Question

我要建立的MySQL查询需要一些帮助。

这是我有的表：

+----+-----------+---------+-----------+---------+------------+-----------+
| 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    |
+----+-----------+---------+-----------+---------+------------+-----------+

为了使所有这些对于原因有意义，我需要使用第一个SELECT限制三个条件的结果来获取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，但是这次仅在两个条件下进行限制，并且不包括第一个SELECT的结果，依此类推。

任何想法如何实现这一目标？ 我尝试了几种不同的查询，包括UNION但是以某种方式无法使其显示我所需的结果。

Answer 1

使用选择联合而不是

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

我缺少的东西或者是OR不够？

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")
       )
;

...非常确定所有这些城市，城市组合的标准也可以简化。

而且， UNION应该为您工作了，并且可能更快，因为使用OR时MySQL趋于几乎完全忽略索引。

---

编辑：您可以在上面的任一查询中获得带有“ ORDER BY和“ LIMIT 6 ”的“前六个”：

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，则返回的六个结果可能会有所不同，但将与第一个查询/条件不同（ 当然，MySQL并不真正保证查询会返回无论如何，在连续执行时，结果将以相同的顺序排列 。）