离开加入mysql问题

Question

This is my query:

SELECT *
  FROM (
SELECT users.id, users.name, users.gender
       users.gender_preference, users.about_me
  FROM `users`
LEFT JOIN users_purchase ON users.id = users_purchase.user_id
     WHERE users.id != 20
       AND users.status = 1
       AND users.birthdate <= '1996-03-18' AND users.birthdate >= '1934-03-18'   AND users.gender = '2'                                    
  GROUP BY users.id
      ) AS myTable

I have another table that has this fields:

id (primary),theBlocker, whoToBlock

I need to remove from my query results the users ('whoToBlock') that the blocker ('theBlocker') blocked. Any idea?

Answer 1

 SELECT *
  FROM (
  SELECT users.id, users.name, users.gender
         users.gender_preference, users.about_me
  FROM  `users`
  LEFT JOIN users_purchase ON users.id = users_purchase.user_id
  LEFT JOIN OTHERTABLE ON whoToBlock = users.id
  WHERE users.id != 20
  AND users.status = 1
  AND users.birthdate <= '1996-03-18' 
  AND users.birthdate >= '1934-03-18'   
  AND users.gender = '2' 
  AND OTHERTABLE.theBlocker IS NULL
  GROUP BY users.id
 ) AS myTable

I am assuming whoToBlock maps to your user.id and theBlocker is a boolean. Edit these conditions accordingly

Answer 2

I am a little unclear on who is blocking whom. Let me assume, for your example, that you want to exclude any users blocked by user 20 . A simple way to add this to your query is in the where clause:

SELECT u.id, u.name, u.gender, u.gender_preference, u.about_me
FROM `users` u LEFT JOIN
     users_purchase up 
     ON u.id = up.user_id
WHERE u.id <> 20 AND
      u.status = 1 AND
      u.birthdate <= '1996-03-18' AND
      u.birthdate >= '1934-03-18' AND
      u.gender = '2' and
      NOT EXISTS (select 1
                  from blockers b
                  where b.theBlocker = 20 and b.whomToBlock = u.id
                 )                                
GROUP BY users.id;

Note that I also removed the additional layer of subqueries and added table aliases to make the query more readable.