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Databases SQL Reporting by Example Day 1: Joining Tables 7th Grade Science

Posted by kevin hudson
kevin hudson
Courses Plus Student 11,987 Points

Is it a bad approach to use subqueries over CTE and JOINING?

I'm finding out that I can understand joining data through subqueries so much better than understanding CTE and Joining. I understand there is a right time to use other methods but if it produces the same result with less code it should be ok? 

-- Which teacher teaches 7th grade science?
SELECT DISTINCT ID, FIRST_NAME, LAST_NAME FROM TEACHERS 
WHERE ID IN(SELECT TEACHER_ID FROM CLASSES 
            WHERE SUBJECT_ID IN(SELECT ID FROM SUBJECTS 
                                WHERE NAME LIKE "%scien%" AND GRADE = 7) );

2 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

When you start benchmarking query efficiencies, you may discover reasons to choose one method over another, but for now if it works and is readable/maintainable, it should be essentially your choice.

One extra bonus of your approach is that you don't need that "DISTINCT" qualifier.

tafadzwagondo
tafadzwagondo
4,250 Points
tafadzwagondo
tafadzwagondo
4,250 Points

SELECT DISTINCT( FIRST_NAME ||" "|| LAST_NAME) AS FULL_NAME FROM TEACHERS AS t INNER JOIN CLASSES AS c ON t.ID = c.TEACHER_ID WHERE c.SUBJECT_ID IN (SELECT s.ID FROM SUBJECTS AS s WHERE GRADE = "7" AND NAME = "Science")