Joining tables by skipping the intermediate parent table [closed]

We’ve tables adm_app, quals_data to which personal_data is a parent table. We are retrieving data from another table sub_marks which has a foreign key of quals_data and the query is like this

select
      sub_marks.obtain_marks,
      sub_marks.convertion_marks,
      sub_marks.max_marks
from sub_marks
inner join quals_data ON quals_data.id = sub_marks.quals_data_id
inner join adm_app on quals_data.personal_data_id = adm_app.personal_data_id
where adm_app.app_no = 2000;

You can see that we’ve skipped the join with personal_data because we are not using its data anywhere. Is this a good way of writing a query? Previously we wrote query like this

select
      sub_marks.obtain_marks,
      sub_marks.convertion_marks,
      sub_marks.max_marks
from sub_marks
inner join quals_data ON quals_data.id = sub_marks.quals_data_id
inner join personal_data ON personal_data.id = quals_data.personal_data_id
inner join adm_app on adm_app.personal_data_id = personal_data.id
where adm_app.app_no = 2000;

Your changes to the query are good changes.

Just because the both adm_app and quals_data have the same child relationship to the personal_data table does not mean you have to include the personal_data table in a join if there’s no relevant data on it.

You should run both of your queries with the query-plan EXPLAIN to show the difference in the queries. Avoiding the join will make for a simpler query with better performance.

Having said that, what about the rest of your query, are there improvements that can be made? Nothing big, really. I am not a big fan of snake_case for table and column names, but it is more important that you are consistent, and neat with the concept.

If I were to have any complaints, it would just be two really small things:

• a spelling error…. I know, it’s seriously pedantic, but in my “real job” I would point out the error soon because it is the sort of thing that is hard to correct later… convertion should be spelled conversion
• abbreviations should be consistent in names. Since you have personal_data and fully named columns like convertion_marks, then it follows that you should not have abbreviations for adm_app and quals_data. Those should be full names.

As you can tell, the only issues I can see are really trivial.