Question

Can someone explain the difference between these 2 types of joins and how to visualize them? Not sure when to use which…

Ex1

select a.f1, a.f2, b.f1, b.f2
from table_a a
inner join table_c c
    on a.id = c.id
inner join table_b b
    on c.id = b.id

Ex 2

SELECT a.au_lname,
       a.au_fname,
       t.title
FROM   authors a
       INNER JOIN titleauthor ta
         ON a.au_id = ta.au_id
       JOIN titles t
         ON ta.title_id = t.title_id
WHERE  t.type = 'trad_cook'
ORDER  BY t.title ASC 

Using this unrelated venn diagram- what do these 2 queries return?

Answer 1

It simply means that you are joining three tables in your SELECT statement.

• authors is joined with titleauthor
• titleauthor is joined with titles

To learn more about joins, please see the article below,

• Visual Representation of SQL Joins