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
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)
I get the Cartesian product of the values specified for f1 and f2 in the IN clauses, ie the rows with all possible combinations for f1 = 'a' or 'b', and f2 = 30, 20, hence row 1 is also selected.
In short, I'm need something like:
SELECT * FROM my_table WHERE (f1,f2) IN (('a',30), ('b',20))
only with a valid SQL syntax :-)
Any ideas?
That is valid syntax.
If you don't like it some other alternatives are:
SELECT * FROM my_table
WHERE (f1, f2) = ('a', 30)
OR (f1, f2) = ('b', 20)
Or using a join:
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
SELECT * FROM my_table WHERE (f1= 'a' AND f2=30) OR (f1='b' AND f2=20);
A rough but practical way is to use string concatenation:
SELECT *
FROM MyTable
WHERE CONCAT(f1, '_', f2) IN ('a_30', 'b_20')
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