Select 最近的 MAX() 和 MIN() - WebSQL

Question

我正在构建一个练习网络应用程序，我正在使用两个这样的表：

Table 1: weekly_stats

| id |    code      |      type          |       date |     time |
|----|--------------|--------------------|------------|----------|
|  1 |           CC |                  1 | 2015-02-04 | 19:15:00 |
|  2 |           CC |                  2 | 2015-01-28 | 19:15:00 |
|  3 |          CPC |                  1 | 2015-01-26 | 19:15:00 |
|  4 |          CPC |                  1 | 2015-01-25 | 19:15:00 |
|  5 |           CP |                  1 | 2015-01-24 | 19:15:00 |
|  6 |           CC |                  1 | 2015-01-23 | 19:15:00 |
| .. |          ... |                ... |    ...     |    ...   |

Table 2: global_stats

| id | exercise_number |correct |   wrong   |
|----|-----------------|--------|-----------|
|  1 |             138 |      1 |         0 |
|  2 |             246 |      1 |         0 |
|  3 |             988 |      1 |        10 |
|  4 |              13 |      5 |         0 |
|  5 |               5 |      4 |         7 |
|  6 |               5 |      4 |         7 |
| .. |             ... |    ... |       ... |

我想要得到 MAX（正确-错误）和 MIN（正确-错误），现在我正在处理这个查询：

SELECT
  exercise_number,
  date,
  time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id 
WHERE correct - wrong = (SELECT MAX(correct - wrong) from global_stats)
UNION
SELECT
  exercise_number,
  date,
  time
FROM weekly_stats AS w JOIN global_stats AS g
ON w.id=g.id 
WHERE correct - wrong = (SELECT MIN(correct - wrong) from global_stats);

此查询运行良好，除了一件事：当 "WHERE correct - wrong = (SELECT MIN(correct - wrong)[...]" 选择多行时，选择的行是第一行，但我想返回最新的 (换句话说：按日期时间（日期，时间）排序。这可能吗？

谢谢！

Answer 1

我想你可以这样解决：

SELECT * FROM (
    SELECT
      1 as sort_column,
      exercise_number,
      date,
      time
    FROM weekly_stats AS w JOIN global_stats AS g
    ON w.id=g.id 
    WHERE correct - wrong = (SELECT MAX(correct - wrong) from global_stats)
    ORDER BY date DESC, time DESC
    LIMIT 1 ) as a
UNION
SELECT * FROM (
    SELECT
      2 as sort_column,
      exercise_number,
      date,
      time
    FROM weekly_stats AS w JOIN global_stats AS g
    ON w.id=g.id 
    WHERE correct - wrong = (SELECT MIN(correct - wrong) from global_stats)
    ORDER BY date DESC, time DESC
LIMIT 1) as b
ORDER BY sort_column;

这里是关于 UNION 工作原理的documentation。

Select 最近的 MAX() 和 MIN() - WebSQL

Select most recent MAX() and MIN() - WebSQL

mysql

sqlite

web-sql