Question

如果我使用where where
，我的查询工作正常

select a.mnth,count(b.month) from table1  b right join (SELECT 'January' mnth,'01' as set_or
            UNION ALL
            SELECT 'February' mnth,'02' as set_or
            UNION ALL
            SELECT 'March' mnth,'03' as set_or
            UNION ALL
            SELECT 'APRIL' mnth,'04' as set_or
            UNION ALL
            SELECT 'MAY' mnth,'05' as set_or
                        UNION ALL
            SELECT 'JUNE' mnth,'06' as set_or
                        UNION ALL
            SELECT 'JULY' mnth,'07' as set_or
                        UNION ALL
            SELECT 'AUGUST' mnth,'08' as set_or
                        UNION ALL
            SELECT 'SEPTEMBER' mnth,'09' as set_or
                        UNION ALL
            SELECT 'OCTOBER' mnth,'10' as set_or
            UNION ALL
            SELECT 'NOVEMBER' mnth,'11' as set_or
            UNION ALL
            SELECT 'DECEMBER' mnth,'12' as set_or
            ) a on a.mnth = b.month   group by a.mnth  order by a.set_or asc;



+-----------+----------------+
| mnth      | count(b.month) |
+-----------+----------------+
| January   |              0 |
| February  |              0 |
| March     |              2 |
| APRIL     |              1 |
| MAY       |              0 |
| JUNE      |              1 |
| JULY      |              1 |
| AUGUST    |              0 |
| SEPTEMBER |              0 |
| OCTOBER   |              0 |
| NOVEMBER  |              0 |
| DECEMBER  |              0 |
+-----------+----------------+

但我使用condion在同一个查询中它不显示0反对每个月的名字

select a.mnth,count(b.month) from table1 b right join (SELECT 'January' mnth,'01' as set_or
            UNION ALL
            SELECT 'February' mnth,'02' as set_or
            UNION ALL
            SELECT 'March' mnth,'03' as set_or
            UNION ALL
            SELECT 'APRIL' mnth,'04' as set_or
            UNION ALL
            SELECT 'MAY' mnth,'05' as set_or
                        UNION ALL
            SELECT 'JUNE' mnth,'06' as set_or
                        UNION ALL
            SELECT 'JULY' mnth,'07' as set_or
                        UNION ALL
            SELECT 'AUGUST' mnth,'08' as set_or
                        UNION ALL
            SELECT 'SEPTEMBER' mnth,'09' as set_or
                        UNION ALL
            SELECT 'OCTOBER' mnth,'10' as set_or
            UNION ALL
            SELECT 'NOVEMBER' mnth,'11' as set_or
            UNION ALL
            SELECT 'DECEMBER' mnth,'12' as set_or
            ) a on a.mnth = b.month  where b.year like '2016' group by a.mnth  order by a.set_or asc;


+-------+----------------+
| mnth  | count(b.month) |
+-------+----------------+
| March |              2 |
| APRIL |              1 |
| JUNE  |              1 |
| JULY  |              1 |
+-------+----------------+

这是我的表格描述

表1;

+-------------+---------------+------+-----+-------------------+-----------------------------+
| Field       | Type          | Null | Key | Default           | Extra                       |
+-------------+---------------+------+-----+-------------------+-----------------------------+
| month       | varchar(100)  | NO   |     | NULL              |                             |
| Year        | int(100)      | NO   |     | NULL              |                             |
+-------------+---------------+------+-----+-------------------+------------------------------

任何人都可以请告诉我，我怎么能得到0计数是任何月份没有存在？

Answer 1

我已重新排列表格的顺序（代码中的外观），并分别将RIGHT JOIN更改为LEFT JOIN。将WHERE子句约束放入JOIN中，以便不暗示INNER JOIN：

select 
  a.mnth,
  count(b.month)
from (
  SELECT 'January' mnth,'01' as set_or
  UNION ALL
  SELECT 'February' mnth,'02' as set_or
  UNION ALL
  SELECT 'March' mnth,'03' as set_or
  UNION ALL
  SELECT 'APRIL' mnth,'04' as set_or
  UNION ALL
  SELECT 'MAY' mnth,'05' as set_or
  UNION ALL
  SELECT 'JUNE' mnth,'06' as set_or
  UNION ALL
  SELECT 'JULY' mnth,'07' as set_or
  UNION ALL
  SELECT 'AUGUST' mnth,'08' as set_or
  UNION ALL
  SELECT 'SEPTEMBER' mnth,'09' as set_or
  UNION ALL
  SELECT 'OCTOBER' mnth,'10' as set_or
  UNION ALL
  SELECT 'NOVEMBER' mnth,'11' as set_or
  UNION ALL
  SELECT 'DECEMBER' mnth,'12' as set_or
  ) a 
left join donation_entry b on 
  a.mnth = b.month 
  and b.year = '2016' -- here is the change
group by a.mnth
order by a.set_or asc;

请注意，我还用等号运算符like替换了=，因为没有用于部分匹配的通配符，它基本上是相同的，可以避免混淆。

如果mysql中group by语句中不存在值，如何显示0计数？

1 个答案: