Question

我有一个这样的个人资料表

|--------|-----------|
| People | Favorite  |
|--------|-----------|
|   A    |   Movie   |
|   B    |   Movie   |
|   B    |  Jogging  |
|--------|-----------|

问：如何找回最喜欢电影而不是慢跑的人？

在此表中，结果仅为人物A。

尽管我想到了这个

select People from Profile
where
People
in
(select People from Profile
where favorite='Movie')
and
People
not in
(select People from Profile
where favorite='Jogging')

但是，任何建议或答案（不使用join或union子句）似乎都可以更好？

Answer 1

https://www.db-fiddle.com/f/rboiDpxxbABCpjtduEz7uY/1

SELECT People 
FROM `profile`
GROUP BY people
HAVING SUM('Movie' = favorite) > 0
   AND SUM('Jogging' = favorite) = 0

Answer 2

有很多方法。虽然可以使用UNION，但它相当混乱且效率低下。 MySQL没有MINUS子句，该子句可以使查询相当容易理解。

您可以汇总数据：

SELECT people
, MAX(IF(favorite='jogging', 1, 0)) as jogging
, MAX(IF(favorite='movie', 1, 0)) as movie
FROM profile
GROUP BY people
HAVING movie=1 AND jogging=0

或使用外部联接：

SELECT m.people
FROM profile m
LEFT JOIN
 ( SELECT j.people
 FROM joggers j
 WHERE j.favorite='jogging' ) joggers
ON m.people=joggers.people
WHERE joggers.people IS NULL
AND m.favorite='movies'

使用NOT IN / NOT EXISTS可以使语法更清晰，但效率仍然很低。

Answer 3

有几种查询模式将返回满足规范的结果。

我们可以将NOT EXISTS与相关子查询一起使用：

SELECT p.people 
  FROM profile p 
 WHERE p.favorite = 'Movie' 
   AND NOT EXISTS ( SELECT 1
                      FROM profile q
                     WHERE q.favorite = 'Jogging' 
                       AND q.people   = p.people   /* related to row in out query */
                  )
 ORDER
    BY p.people

等效的结果也可以通过 anti-join 模式完成：

SELECT p.people 
  FROM profile p
  LEFT
  JOIN profile q
    ON q.people   = p.people
   AND q.favorite = 'Jogging'
 WHERE q.people IS NULL
   AND p.favorite = 'Movie'
 ORDER BY p.people

另一种选择是条件聚合。无法保证唯一性和一些MySQL速记：

SELECT p.people
  FROM profile p
 GROUP
    BY p.people
HAVING 1 = MAX(p.favorite='Movie')
   AND 0 = MAX(p.favorite='Jogging')

用于条件聚合的更具可移植性，更符合ANSI标准的语法：

SELECT p.people
  FROM profile p
 GROUP
    BY p.people
HAVING 1 = MAX(CASE p.favorite WHEN 'Movie'  THEN 1 ELSE 0 END)
   AND 0 = MAX(CASE p.favorite WHEN Jogging' THEN 1 ELSE 0 END)

Answer 4

当您要在同一列中具有多个条件时，这是一个常见问题。我已经回答了here，并且还有其他方法，例如相交和子查询。

SELECT people, GROUP_CONCAT(favorite) as fav
FROM profile
GROUP BY people
HAVING fav REGEXP 'Movie'
AND NOT fav REGEXP 'Jogging';

Answer 5

使用group by people并检查favorite的最小值和最大值为'Movie'：

select people from tablename
where favorite in ('Movie', 'Jogging')
group by people
having min(favorite) = 'Movie' and max(favorite) = 'Movie'

跨多行的MySQL条件语句

5 个答案: