通过多列进行SQL过滤 [英] SQL filtering by multiple columns
问题描述
我有一个MySql表,我想查询其中对列在特定集中的行. 例如,假设我的表格如下所示:
I have a MySql table, which I want to query for rows in which pairs of columns are in a specific set. For example, say my table looks like this:
id | f1 | f2
-------------
1 | 'a' | 20
2 | 'b' | 20
3 | 'a' | 30
4 | 'b' | 20
5 | 'c' | 20
现在,我希望提取其中(f1,f2)对为('a',30)或('b',20)的行,即行2,3, 4,我也希望使用"IN"样式的过滤器来完成此操作,因为我可能有很多对要提取.如果我尝试类似的事情:
Now, I wish to extract rows in which the pair (f1, f2) are either ('a',30) or ('b', 20), namely rows 2,3,4. I also wish to do it using an 'IN' style filter, as I may have many pairs to fetch. If I try something like:
SELECT * FROM my_table WHERE f1 IN ('a','b') AND f2 IN (30, 20)
SELECT * FROM my_table WHERE f1 IN ('a','b') AND f2 IN (30, 20)
我得到IN子句中为f1和f2指定的值的笛卡尔积,即具有f1 ='a'或'b'的所有可能组合的行,以及f2 = 30、20,因此行1为也被选中.
I get the Cartesian product of the values specified for f1 and f2 in the IN clauses, i.e. the rows with all possible combinations for f1 = 'a' or 'b', and f2 = 30, 20, hence row 1 is also selected.
简而言之,我需要类似的东西:
In short, I'm need something like:
SELECT * FROM my_table WHERE (f1,f2) IN (('a',30), ('b',20))
SELECT * FROM my_table WHERE (f1,f2) IN (('a',30), ('b',20))
仅使用有效的SQL语法:-)
only with a valid SQL syntax :-)
有什么想法吗?
推荐答案
是有效语法.
如果您不喜欢它,则还有其他选择:
If you don't like it some other alternatives are:
SELECT * FROM my_table
WHERE (f1, f2) = ('a', 30)
OR (f1, f2) = ('b', 20)
或使用联接:
SELECT *
FROM my_table T1
(
SELECT 'a' AS f1, 30 AS f2
UNION ALL
SELECT 'b', 20
) T2
ON T1.f1 = T2.f1 AND T1.f2 = T2.f2
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