MySQL 多个 SELECT 查询在同一个 table 上使用不同的 WHERE 子句

Question

我需要一些关于我正在尝试构建的 MySQL 查询的帮助。

这是 table 我有：

+----+-----------+---------+-----------+---------+------------+-----------+
| 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 table 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    |
+----+-----------+---------+-----------+---------+------------+-----------+

为了让所有这些都明白为什么，我需要获得 Apple 的所有结果，第一个 SELECT 限制三个条件。然后，我需要使用第二个 SELECT 获取 Apple 的所有结果，但这次仅限于两个条件，并排除第一个 SELECT 的结果，依此类推。

知道如何实现吗？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并集而不是

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

我是不是遗漏了什么或者 OR 还不够？

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")
       )
;

...很确定所有这些 vit、城市组合的标准也可以压缩。

此外，UNION 应该对您有用，而且可能更快，因为 MySQL 在使用 OR 时几乎完全忽略索引。

编辑：您可以在上述任一查询中使用 ORDER BY 和 LIMIT 6 获得 "first" 六个，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

...由于各个查询没有顺序，如果第一个条件产生超过六个结果，则六个 returned 可能不同，但将来自第一个 query/condition（当然，MySQL 实际上并不能保证查询 return 结果在连续执行时的顺序相同 。）

MySQL 多个 SELECT 查询在同一个 table 上使用不同的 WHERE 子句

MySQL Multiple SELECT queries with different WHERE clause on the same table

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