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MySQL选择按值计数？

2024-05-13 22:44:04 402

您可以COUNT()为此使用功能。让我们首先创建一个演示表

mysql> create table countValueDemo
   -> (
   -> ShippingDatetime datetime,
   -> FirstValue int,
   -> SecondValue int
   -> );

使用insert命令在表中插入一些记录。查询如下-

mysql> insert into countValueDemo values('2019-01-23',1,2);
mysql> insert into countValueDemo values('2017-02-21',NULL,2);
mysql> insert into countValueDemo values('2016-04-12',1,NULL);

使用select语句显示表中的所有记录。查询如下-

mysql> select *from countValueDemo;

以下是输出

+---------------------+------------+-------------+
| ShippingDatetime    | FirstValue | SecondValue |
+---------------------+------------+-------------+
| 2019-01-23 00:00:00 |          1 |           2 |
| 2017-02-21 00:00:00 |       NULL |           2 |
| 2016-04-12 00:00:00 |          1 |        NULL |
+---------------------+------------+-------------+
3 rows in set (0.00 sec)

这是选择按值计数的查询

mysql> SELECT ShippingDatetime,
   -> COUNT(*),
   -> COUNT( IF( FirstValue = 1, 1, NULL ) ),
   -> COUNT( IF( SecondValue = 2, 1, NULL ) )
   -> FROM countValueDemo;

以下是输出

+---------------------+----------+----------------------------------------+-----------------------------------------+
| ShippingDatetime    | COUNT(*) | COUNT( IF( FirstValue = 1, 1, NULL ) ) | COUNT( IF( SecondValue = 2, 1, NULL ) ) |
+---------------------+----------+----------------------------------------+-----------------------------------------+
| 2019-01-23 00:00:00 |        3 |                                      2 |                                       2 |
+---------------------+----------+----------------------------------------+-----------------------------------------+
1 row in set (0.08 sec)

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MySQL选择按值计数？

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