Question

我想要一个查询，该查询给出日期为“ april2018”的重复区域计数查询的预期输出

显示的表格

+---------+--------------+
| region  |     Date     |
+---------+--------------+
| africa  |    april2018 |
| africa  |    may2018   |
| africa  |    may2018   |
| america |   jan2018    |
| america |   jan2018    |
| africa  |    april2018 |
| africa  |    may2018   |
| africa  |    may2018   |
| india   |    jan2018   |
| india   |    jan2018   |
+---------+--------------+

预期结果

+----------+---------+
|  region  |  Count  |
+----------+---------+
|  africa  |       2 |
|  america |       0 |
|  india   |       0 |
+----------+---------+

Answer 1

将case when与计数一起使用

select region, coalesce(count(case when Date = 'april2018' then 1 end),0) as count
from tablname
group by region

Answer 2

您可以根据要求执行以下查询以获取结果。

SELECT Region, COUNT(*) AS Cnt
FROM Region
WHERE Date = 'April2018'
GROUP BY Region

Answer 3

我添加了一个主键以获得您的预期结果

mysql> select * from region_date;
+---------+-----------+----+
| region  | date      | id |
+---------+-----------+----+
| africa  | april2018 |  1 |
| africa  | may2018   |  2 |
| africa  | may2018   |  3 |
| america | jan2018   |  4 |
| america | jan2018   |  5 |
| africa  | april2018 |  6 |
| africa  | may2018   |  7 |
| africa  | may2018   |  8 |
| india   | jan2018   |  9 |
| india   | jan2018   | 10 |
+---------+-----------+----+
10 rows in set (0.00 sec)

mysql> select count(sub), inn.region from 
        (select 
          i.region, 
          (select s.date from region_date s where   s.id = i.id  and s.date = 'april2018' limit 1)  as sub, 
          date 
         from region_date i) as inn group by region;
+------------+---------+
| count(sub) | region  |
+------------+---------+
|          2 | africa  |
|          0 | america |
|          0 | india   |
+------------+---------+
3 rows in set (0.00 sec)

Answer 4

这是另一种简单的方法：

SELECT Region, SUM(Date='april2018') as Count
FROM TableName
GROUP BY Region;

获取列中的计数

4 个答案: