SQL 选择其中 A 等于 B 和 C

Question

name | course
Jay | LAWS0001
Mark | LAWS0002
Sam | LAWS0002
Alice | LAWS0001
Ryan | LAWS0001
Ryan | LAWS0002

Hey guys, I've got this database and I want to only select the names that take both 'LAWS0001' and 'LAWS0002'. So from this example, it should select 'Ryan' because he's the only person to take both courses. I tried IN operator:

SELECT name
FROM student
WHERE course IN ('LAWS0001', 'LAWS0002')

but this takes everyone because everyone is taking either of the courses.

Is there an operator for my problem?

Answer 1

You can use your existing query, using a GROUP BY clause to COUNT the number of distinct courses each student is taking in the set ('LAWS0001', 'LAWS0002') and only selecting those students where the count is 2:

SELECT name
FROM student
WHERE course IN ('LAWS0001', 'LAWS0002')
GROUP BY name
HAVING COUNT(DISTINCT course) = 2

Demo on SQLFiddle