[leetcode database 1050] actors and directors who have cooperated at least three times (simple question)

One 、 subject

Two 、 Code

• Because it requires the cooperation of actors and directors That is to say actor_id and director_id Must be the same to meet the conditions So we need to add two grouping conditions groupby. Because if the grouping condition is not added director_id that COUNT(*) What counts is the number of collaborations between the actor and all directors Rather than the number of collaborations with various directors In the fourth example of the test, there will be errors .
• use GROUP BY After grouping, you can use HAVING Take out the desired group .SQL In the use of HAVING When clause SELECT The order of statements is ：FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY.

# Write your MySQL query statement below
SELECT actor_id, director_id 
FROM ActorDirector 
GROUP BY actor_id, director_id
HAVING COUNT(*) >= 3;