Question

There is a table called client_application with data something like this;

Id   user_id   name      creationDate
---------------------------------------
1    5         name1     date
2    4         name2     date
3    98        name3     date

And also a table called application_status which holds the status feed of application(application_id is foreign key);

Id   aplication_id   status            other_columns      creationDate
----------------------------------------------------------------------
1    1       APPLICATION_SUMITTED      data               date
2    2       APPLICATION_SUMITTED      data               date
3    1       APPLICATION_RECEVIED      data               date
4    1       BANK_APPROVED             data               date
5    3       APPLICATION_SUMITTED      data               date
6    2       APPLICATION_RECEVIED      data               date

I want to query the application by their status. For example get the newest submitted applications? Or get the applications which the bank approved.

How can I implement such an SQL query?

I have tried thi;

SELECT *
FROM (SELECT * FROM application_status ORDER BY creationDate DESC) t1
LEFT JOIN client_application on client_application.id = t1.application_id
GROUP BY t1.application_id;

Which is fine, I can get the applications with their latest status but when I try to put a where clause in it;

SELECT *
FROM (SELECT * FROM application_status ORDER BY creationDate DESC) t1
LEFT JOIN client_application on client_application.id = t1.application_id
where t1.status = 'APPLICATION_SUBMITTED'
GROUP BY t1.application_id;

It returns all application_status has APPLICATION_SUBMITTED status column..
It returns application_id 1 item ( check the table above) but as you can see, application with the id number 1 has APPLICATION_RECEIVED status as latest status item.. So I would not expect this one in result set.

Maybe my approach is totally wrong. I’m open for any solution.

Thanks.

Answer 1

My advice is to improve the design of your database by creating a new table ‘Status’ for example :

Id   Label
1    APPLICATION_SUBMITTED
2    APPLICATION_RECEIVED
3    BANK_APPROVED 

You have to give the labels a logical order, and you refer to this table in your status or main table.

It will be easier to retrieve the status of an application ( where Status.Id < 3 to select all non-approved applications, or where Status.Id > 1 to select all application that are at least received ).

It is also better for maintenance purpose. This kind of logic applies in a lot of cases, and you should consider to spend a bit more time to design your data models, so you won’t spend more time resolving this kind of issue your are facing now.