Question

我想知道是否有办法简化以下SQL语句。这是我的桌子。

| SID | name | l1 | l2 | sch |
|  1  | john |    |    | sch |
|  2  | mary | l1 |    |     |
|  3  | zack | l1 | l2 |     |
|  4  | paul | l1 | l2 | sch |

填充l1或l2，或者两者都可以填充

并非每个'sch'都有值

我所做的是计算每日汇总表，但我是通过PHP完成的，我想知道是否可以使用SQL来完成。所以，例如，

- Total count (This is just count(name))
- Count(sch)
- If !empty (l1) OR !empty (l2) THEN l + 1

所以现在，基于以上

 Total count = 4
 count(sch) = 2
 count(l1 || l2) = 3

可以在SQL中完成吗？

Answer 1

您没有说l1，l2和sch列是否包含NULL。

如果这些列不能包含NULL，则mysql查询将如下：

SELECT COUNT(*) AS `count`, SUM(sch<>'') AS count_sch,
SUM(l1<>'' OR l2<>'') AS count_l
FROM your_table

如果这些列可以包含NULL，则mysql查询将类似于：

SELECT COUNT(*) AS `count`, SUM(sch IS NOT NULL) AS count_sch,
SUM(l1 IS NOT NULL OR l2 IS NOT NULL) AS count_l
FROM your_table

Answer 2

select count(name) name_count,
       count(coalesce(nullif(l1,''), nullif(l2,''))) l1_or_l2_count,
       count(sch) sch_count
  from your_table;

Answer 3

是：

select count(*) as count, count(sch) as school,
       sum(case when l1 is not null or l2 is not null then 1 else 0 end)
from table

简化复杂的计数SQL语句

3 个答案: