在同一列上选择多个条件

Ok, I think I might be overlooking something obvious/simple here... but I need to write a query that returns only records that match multiple criteria on the same column...

好的，我想我可能忽略了一些显而易见的事情……但是我需要编写一个查询，它只返回与同一列上的多个条件匹配的记录……

My table is a very simple linking setup for applying flags to a user ...

我的表是一个非常简单的链接设置，用于向用户应用标志……

ID   contactid  flag        flag_type 
-----------------------------------
118  99         Volunteer   1 
119  99         Uploaded    2 
120  100        Via Import  3 
121  100        Volunteer   1  
122  100        Uploaded    2

etc... in this case you'll see both contact 99 and 100 are flagged as both "Volunteer" and "Uploaded"...

等等……在本例中，您将看到contact 99和100都标记为“志愿者”和“上传”…

What I need to be able to do is return those contactid's ONLY that match multiple criteria entered via a search form...the contactid's have to match ALL chosen flags... in my head the SQL should look something like:

我需要做的是返回那些contactid的唯一匹配通过搜索表单输入的多个条件的。contactid必须匹配所有选择的标志……在我的脑海中，SQL应该是这样的:

SELECT contactid 
 WHERE flag = 'Volunteer' 
   AND flag = 'Uploaded'...

but... that returns nothing... What am I doing wrong here?

但是…返回什么……我在这里做错了什么?

11 个解决方案

#1

You can either use GROUP BY and HAVING COUNT(*) = _:

您可以使用GROUP BY和COUNT(*) = _:

SELECT contact_id
FROM your_table
WHERE flag IN ('Volunteer', 'Uploaded', ...)
GROUP BY contact_id
HAVING COUNT(*) = 2 -- // must match number in the WHERE flag IN (...) list

(assuming contact_id, flag is unique).

(假设contact_id是惟一的)。

Or use joins:

或者使用连接:

SELECT T1.contact_id
FROM your_table T1
JOIN your_table T2 ON T1.contact_id = T2.contact_id AND T2.flag = 'Uploaded'
-- // more joins if necessary
WHERE T1.flag = 'Volunteer'

If the list of flags is very long and there are lots of matches the first is probably faster. If the list of flags is short and there are few matches, you will probably find that the second is faster. If performance is a concern try testing both on your data to see which works best.

如果标志的列表很长，并且有很多匹配项，那么第一个可能会更快。如果标记列表很短，并且几乎没有匹配，那么您可能会发现第二个标记更快。如果性能是一个问题，请尝试在数据上测试这两个数据，看看哪一个最有效。

11 个解决方案

#1

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