MySQL query to get all items that do not belong to another table

Question

I have a problem that I haven't been able to resolve for some hours.

I have 3 tables:

• Process

  \n+----+----------+----------------+--------+-------------+---------------+-------------+---------+------+ \n|  id |  name |  description |  active |  responsible |  informByEmail |  informBySms |  remarks |  icon | \n+----+----------+----------------+--------+-------------+---------------+-------------+---------+------+ \n|  4 |  Process1 |  TestDecriptino |  1 |  0 |  0 |  0 |  0 |  NULL | \n|  5 |  Process2 |  test |  0 |  0 |  0 |  0 |  test |  NULL | \n|  6 |  Process3 |  12322 |  1 |  0 |  0 |  0 |  12322 |  NULL | \n|  7 |  Process4 |  222222222222 |  0 |  0 |  0 |  0 |  2222222 |  NULL | \n|  9 |  Process5 |  sgdasad |  1 |  0 |  1 |  0 |  dhds |  NULL | \n+----+----------+----------------+--------+-------------+---------------+-------------+---------+------+ \n

• Systems

  \n+----+---------+-------------+--------+-------------------+---------------+-------------+---------+------+ \n|  id |  name |  description |  active |  responsibleUserId |  informByEmail |  informBySms |  remarks |  icon | \n+----+---------+-------------+--------+-------------------+---------------+-------------+---------+------+ \n|  2 |  Sistem1 |  fdjgf |  1 |  1 |  1 |  1 |  0 |  NULL | \n|  6 |  Sistem2 |  koam |  0 |  3 |  1 |  0 |  SADGS |  NULL | \n+----+---------+-------------+--------+-------------------+---------------+-------------+---------+------+ \n

• Process_Systems

  \n+----+-----------+----------+--------+---------+ \n|  id |  processId |  systemId |  active |  remarks | \n+----+-----------+----------+--------+---------+ \n|  4 |  4 |  2 |  1 |  aa | \n|  8 |  7 |  2 |  1 |  aa | \n|  11 |  9 |  2 |  1 |  aa | \n|  15 |  4 |  6 |  0 |  aa | \n+----+-----------+----------+--------+---------+ \n

I have a method to which processID is a parameter and must somehow filter all Process_Systems by that ID and then get Systems which do not belong to the Process_Systems table.

Answer 1

• One way would be to use a NOT IN subquery :

   SELECT * FROM Systems WHERE id NOT IN ( SELECT systemid FROM Process_Systems WHERE processId = ? ); 

• Another would be to use a NOT EXISTS subquery :

   SELECT * FROM Systems WHERE NOT EXISTS ( SELECT * FROM Process_Systems WHERE systemId = Systems.id AND processId = ? ); 

• A third way would be to use an outer join :

   SELECT Systems.* FROM Systems LEFT JOIN Process_Systems ps ON ps.systemId = Systems.id AND ps.processId = ? WHERE ps.systemId IS NULL; 

See them on sqlfiddle .

For an analysis of the respective performance differences, see @Quassnoi's blog articles:

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL

• LEFT JOIN / IS NULL vs. NOT IN vs. NOT EXISTS: nullable columns