Question

我遇到使用内部选择的问题，输出不太正确。任何帮助将不胜感激。

这是我的SQLFiddle示例。

这是我正在使用的查询。

SELECT 
t.event as event_date,
count((
    SELECT
        count(s.id)
    FROM mytable s
    WHERE s.type = 2 AND s.event = event_date
)) AS type_count,
count((
    SELECT
        count(s.id)
    FROM mytable s
    WHERE s.type != 3 AND s.event = event_date
)) as non_type_count
FROM mytable t
WHERE t.event >= '2013-10-01' AND t.event <= '2013-10-08'
GROUP BY t.event

我目前的输出：

October, 01 2013 00:00:00+0000 / 2 / 2

October, 03 2013 00:00:00+0000 / 1 / 1

The output I am trying to get:

October, 01 2013 00:00:00+0000 / 1 / 2

October, 03 2013 00:00:00+0000 / 0 / 0

因此，如果你看看我试图使用的查询，我基本上就是这样尝试在日期范围内查询表，然后使用内部选择获取与该类型匹配的行。感谢您的帮助。

Answer 1

可以简化一点并使用条件聚合排除子选择：

SELECT 
    t.event as event_date,
    SUM(t.type = 2) AS type_count,
    SUM(t.type != 3)AS non_type_count
FROM mytable t
WHERE t.event >= '2013-10-01' AND t.event <= '2013-10-08'
GROUP BY t.event

演示：SQL Fiddle

这适用于MySQL，因为表达式返回1或0表示true / false。在其他数据库中，您可以通过SUM(CASE WHEN type=2 THEN 1 END)

实现相同的目标

Answer 2

尝试这种方式：

SELECT 
    t.event as event_date,
    SUM( case when type = 2 then 1 else 0 end )
       AS type_count,
    SUM( case when type != 3 then 1 else 0 end )
       as non_type_count
FROM mytable t
WHERE t.event >= '2013-10-01' AND t.event <= '2013-10-08'
GROUP BY t.event

演示： - ＆gt; http://sqlfiddle.com/#!2/19f3d/13

Answer 3

您正在计算一个计数（count(select count(...）。试试这个：

SELECT 
    t.event as event_date,
    (SELECT
            count(s.id)
        FROM mytable s
        WHERE s.type = 2 AND s.event = event_date
    ) AS type_count,
    (SELECT
            count(s.id)
        FROM mytable s
        WHERE s.type != 3 AND s.event = event_date
    ) as non_type_count
FROM mytable t
WHERE t.event >= '2013-10-01' AND t.event <= '2013-10-08'
GROUP BY t.event

使用内部选择查询计数

3 个答案: