Question

+-------------------+---------------------+------+-----+---------+----------------+
| RowId             | MSGID| Received| UID | Default |                |
+-------------------+---------------------+------+-----+---------+----------------+
| 1                 | 1    | NO      | 1   | NULL    |                | 
| 2                 | 1    | YES     | 3   | NULL    |                | 
| 3                 | 1    | YES     | 4   | NULL    |                | 
| 4                 | 1    | YES     | 5   | NULL    |                | 
| 5                 | 5    | YES     | 2   | NULL    |                | 
| 6                 | 2    | YES     | 8   | NULL    |                | 
| 7                 | 1    | YES     | 9   | NULL    |                | 
+-------------------+---------------------+------+-----+---------+----------------+

这是我在MySQL中的表格。

如何获取MSGID = 1的消息数量和已收到消息的用户数为MSGID = 1的消息数以及未收到消息的用户数为MSGID = 1的消息数量？

我想在一个循环中这样做，以便我可以得到三个值，如[5,4,1]。因此每次页面加载查询时都会检查数据库并更新集合。请帮忙

Answer 1

首先计算MSGID = 1

的消息数

SELECT COUNT(RowID) FROM tableName WHERE MSGID = 1

获取已收到msg的用户数量，其中MSGID = 1

SELECT COUNT(DISTINCT UID) FROM tableName WHERE MSGID = 1

获取未收到MSGID = 1的消息的用户数量

SELECT COUNT(DISTINCT UID) FROM tableName WHERE MSGID =1 AND Received = 'NO'

Answer 2

您可以在一个查询中执行此操作。我没有看到循环的好处？

select count(*)
     , count(distinct uid)
     , count(distinct case when received = 'NO' then uid else null end case)
  from table_name
 where msgid = 1

这应该是多个表，

1）用户，在uid上是截然不同的

2）消息，在msgid上是不同的，收到的是/否。

Answer 3

要使用一个查询来获取它，您可以执行以下所有的联合：

SELECT COUNT(RowID) AS 'Col1', '' AS 'Col2', '' AS 'Col3' 
FROM tableName WHERE MSGID = 1

UNION ALL

SELECT '' AS 'Col1', COUNT(DISTINCT UID) AS 'Col2', '' AS 'Col3' 
FROM tableName WHERE MSGID = 1

UNION ALL

SELECT '' AS 'Col1', '' AS 'Col2' , COUNT(DISTINCT UID) AS 'Col3' 
FROM tableName WHERE MSGID =1 AND Received = 'NO'

希望这对你有用。

如何在mySql数据库中获取行数

3 个答案: