MySQL queries difference sets (missing data) by linking tables based on an associated field

Occasionally encountered some exceptions in the development process , Need to verify data integrity , See if some related data is missing , for example ：

user:

        

profile:

  Above two tables ,user adopt profile_id relation profile Medium id, At the same time, the two tables do not use foreign key Association , When an exception occurs in the program , Or when the business logic is not mandatory , There could be profile Missing data in , It is not easy to view when the amount of data is large ,

At this time, you can find the missing... Through the linked table query profile Corresponding to the data user The data of ：

SELECT u.id,u.name,p.age,p.gender,p.height FROM `user` u LEFT JOIN `profile` p ON u.profile_id=p.id WHERE ISNULL(p.id)

  give the result as follows ：

  Sometimes data query and correction can be done with .