SQL GROUP BY 和 COUNT 条件
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时间：2020-09-01 11:44:00 来源:igfitidea点击:
SQL GROUP BY and a condition on COUNT
提问by CodeGuy
I have the following SQL expression:
我有以下 SQL 表达式：
select id, count(oID) from MyTable group by oID;
and I get something like
我得到类似的东西
+-------+---------------+
| id | count(oID) |
+-------+---------------+
| 002 | 6 |
| 104 | 1 |
| 101 | 1 |
| 908 | 1 |
+-------+---------------+
And now I'd like to pull out the rows (select id) where count(oID)is 1. How can I do this in one SQL statement?
现在我想拉出行 (select id) where count(oID)is 1. 我怎样才能在一个 SQL 语句中做到这一点？
回答by John Woo
Use a HAVINGclause to filter an aggregated column.
使用HAVING子句过滤聚合列。
SELECT id, count(oID)
FROM MyTable
GROUP BY oID
HAVING count(oID) = 1
UPDATE 1
更新 1
wrap the results in a subquery
将结果包装在子查询中
SELECT a.*
FROM tableName a INNER JOIN
(
SELECT id
FROM MyTable
GROUP BY id
HAVING count(oID) = 1
) b ON a.ID = b.ID
