高效SQL查詢連接

Question

我已經執行的子查詢和連接兩個表，然後將其與一個主表加入以下SQL查詢：

SELECT a.id, cgso.sf_guard_user_id as cgso, cgal.sf_guard_user_id as cgal 
FROM table_a a 
JOIN ( SELECT cgso.sf_guard_user_id, cgso.speciality_id 
     FROM table_c g 
     JOIN table_b as cgso 
      ON g.user_id = cgso.sf_guard_user_id and g.group_id = 2) as cgso 
    ON a.speciality_id = cgso.speciality_id 
JOIN ( SELECT cgal.sf_guard_user_id, cgal.speciality_id 
     FROM table_c g 
     JOIN table_b as cgal 
      ON g.user_id = cgal.sf_guard_user_id and g.group_id = 1) as cgal 
    ON a.speciality_id = cgal.speciality_id 

查詢的輸出是：

id | cgso | cgal 
---------------- 
1 | 2 | 54 

輸出是否正常，但是是否有更高效的方法來獲得相同的輸出？任何提示或建議將不勝感激。

謝謝

Answer 1

你應該能夠只是簡化加入...

SELECT a.id, cgso.sf_guard_user_id as cgso, cgal.sf_guard_user_id as cgal 
FROM table_a a 
INNER JOIN table_c g2 ON g1.group_id = 2 
INNER JOIN table_b cgso ON g2.user_id = cgso.sf_guard_user_id AND cgso.specialty_id = a.specialty_id 
INNER JOIN table_c g1 ON g1.user_id = 1 
INNER JOIN table_b cgal ON g1.user_id = cgal.sf_guard_user_id AND cgal.specialty_id = a.specialty_id