MySQL 在两个字段上使用 group by 并在 SQL 中计数
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Using group by on two fields and count in SQL
提问by Marc
I have a table in my mysql db that has two columns: group and subgroup. See below.
我的 mysql 数据库中有一个表，它有两列：组和子组。见下文。
group, subGroup
grp-A, sub-A
grp-A, sub-A
grp-A, sub-B
grp-B, sub-A
grp-B, sub-B
grp-B, sub-B
I am trying to get the number of records for each unique couple group/subGroup.
我正在尝试获取每个唯一夫妇组/子组的记录数。
This is what I expect:
这是我的期望：
group, subGroup, count
grp-A, sub-A, 2
grp-A, sub-B, 1
grp-B, sub-A, 1
grp-B, sub-B, 2
After reading some posts I tried several sql queries using group by, count(), but I do not manage to get the expected result. How can I fix this?
在阅读了一些帖子后，我尝试了使用 group by、count() 的几个 sql 查询，但我没有得到预期的结果。我怎样才能解决这个问题？
回答by Corbin
I think you're looking for: SELECT a, b, COUNT(a) FROM tbl GROUP BY a, b
我认为您正在寻找： SELECT a, b, COUNT(a) FROM tbl GROUP BY a, b
回答by farzane
You must group both columns, group and sub-group, then use the aggregate function COUNT().
您必须对列、组和子组进行分组，然后使用聚合函数COUNT()。
SELECT
group, subgroup, COUNT(*)
FROM
groups
GROUP BY
group, subgroup
回答by user1127214
SELECT group,subGroup,COUNT(*) FROM tablename GROUP BY group,subgroup
