CODEWITHSUNDEEP
sql
teep
teep

Reputation: 53

Inner Join Help - How to order table join?

I have 2 tables:

Class (PK = Tutor)

Columns: ID / Tutor / Room

Teacher (PK FK = Tutor)

Columns: Tutor / Contact

I want to join both tables. Does it matter what order the tables are joined?

ie. 

SELECT Class.ID, Class.Tutor, Teacher.Contact
FROM **Class INNER JOIN Teacher** ON Class.Tutor=Teacher.Tutor

or could I do it the other way round and Teacher INNER JOIN Class instead?

Both tables also share a common column name Tutor. Does it matter if I use Class.Tutor or Teacher.Tutor in the query?

Upvotes: 1

Views: 63

Answers (2)

Adrian Wragg
Adrian Wragg

Reputation: 7401

For an INNER JOIN, the order does not matter; the result set you will get will contain all the rows from both Class and Teacher where the common field Tutor matches, whichever order you specify Teacher and Class.

When you use an OUTER JOIN, the order does matter; I would recommend looking at the answers to What is the difference between Left, Right, Outer and Inner Joins?.

Upvotes: 3

Sarah K
Sarah K

Reputation: 377

Yes, the order matters. Selecting from class and joining Teacher will show only those classes that have a teacher Selecting from teacher and joining Class will show only those teachers that have a class

Depending on what you are trying to achieve you'll know which is most relevant.

I'd recommend using "left join" though, it will give you all the classes even if they don't have teacher assigned etc

FWIW "class" is likely to be a reserved word in your database, server side script and client side scripting languages. I'd find another word for that table name.

Upvotes: -2

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