mysql - 如何在having子句中提出两个条件

Question

我有一个类似于以下的表格:

domain      |   file      | Number 
------------------------------------     
aaa.com     | aaa.com_1   | 111
bbb.com     | bbb.com_1   | 222
ccc.com     | ccc.com_2   | 111
ddd.com     | ddd.com_1   | 222
eee.com     | eee.com_1   | 333

我需要查询共享相同Number且File名称以_1结尾的Domains数量>。我尝试了以下方法:

select count(domain) as 'sum domains', file
from table 
group by Number
having
count(Number) >1 and File like '%\_1'; 

它给了我:

sum domains | file
------------------------------
2           | aaa.com
2           | bbb.com

我希望看到以下内容:

sum domains | file
------------------------------
1           | aaa.com
2           | bbb.com

因为Number 111在File以_1和_2结尾出现一次，所以应该算1仅有的。我怎样才能正确应用我之前所说的两个条件？

Answer 1

如 SELECT 语法中所述:

The HAVING clause is applied nearly last, just before items are sent to the client, with no optimization.

换句话说，它在执行分组操作之后应用(与WHERE相反，后者在任何分组之前执行手术)。请参阅WHERE vs HAVING .

因此，您当前的查询首先根据以下内容形成结果集:

SELECT   COUNT(domain) AS `sum domains`, file
FROM     `table`
GROUP BY Number

查看 sqlfiddle :

| SUM DOMAINS |      FILE |---------------------------|           2 | aaa.com_1 ||           2 | bbb.com_1 ||           1 | eee.com_1 |

As you can see, the values selected for the file column are merely one of the values from each group—as documented under MySQL Extensions to GROUP BY:

The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate.

Your current query then proceeds to filter these results according to your HAVING clause:

HAVING   COUNT(Number) > 1 AND file LIKE '%\_1'

使用上面选择的file值，每个组都符合第二个条件；前两组根据第一个标准进行匹配。因此结果为the complete query是:

| SUM DOMAINS |      FILE |---------------------------|           2 | aaa.com_1 ||           2 | bbb.com_1 |

Following your comments above, you want to filter the records on file before grouping and then filter the resulting groups for those containing more than one match. Therefore use WHERE and HAVING respectively (and select Number instead of file to identify each group):

SELECT   Number, COUNT(*) AS `sum domains`
FROM     `table`
WHERE    file LIKE '%\_1'
GROUP BY Number
HAVING   `sum domains` > 1

查看 sqlfiddle :

| NUMBER | SUM DOMAINS |------------------------|    222 |           2 |