查找每个部门得分最高的2位员工

# 方法一
SELECT a.* 
FROM test AS a
  LEFT JOIN test AS a2 
  ON a.department = a2.department AND a.score <= a2.score
GROUP BY a.name
HAVING COUNT(*) <= 2;

# 方法二
SELECT test.name, test.department, test.score
FROM test
WHERE(SELECT COUNT(*) FROM test as test2
      WHERE test2.department = test.department AND test2.score >= test.score
     ) <= 2


原始数据
# name, department, score
'joe', 'ops', '111'
'aaa', 'ops', '222'
'bbb', 'ops', '333'
'ccc', 'ops', '555'
'ddd', 'dev', '999'
'eee', 'dev', '888'
'fff', 'dev', '777'
'ggg', 'dev', '666'

期望结果:
# name, department, score
'bbb', 'ops', '333'
'ccc', 'ops', '555'
'ddd', 'dev', '999'
'eee', 'dev', '888'

参考链接

• Get top n records for each group of grouped results