Question

I’m rather new to SQL I came across this problem:
I have relationship table where person has power

A has X
A has Z
B has X
B has Y
C has Y
D has Z

I want to select all persons with powers X and Y which is in this case B. Of course I will have a more complex power combination.

Answer 1

Do something like this,

SELECT person
FROM tableName
WHERE power IN ('x', 'y')
GROUP BY Person
HAVING COUNT(*) = 2

• SQLFiddle Demo Link

if unique constraint was not enforce of power on every person, you need to use DISTINCT

SELECT person
FROM tableName
WHERE power IN ('x', 'y')
GROUP BY Person
HAVING COUNT(DISTINCT power) = 2

• SQLFiddle Demo Link (with duplicate)