在LEFT JOIN内的SQL JOIN

Question

Is it possible to join a table inside a table join? If so how do I do it?

I have experience doing standard joins (LEFT JOIN) and have worked out how to join multiple tables but cant see how to join a table inside a table join. Here is my data structure to explain better:

T1 (
    T1_T2
)

T1_T2 (
    T1_T2_id
    T1_T2_T3
)

T1_T2_T3 (
    T1_T2_T3_id
    T1_T2_T3_a
    T1_T2_T3_b
)

Currently my SQL looks like this:

SELECT * FROM T1
    LEFT JOIN T1_T2 
        ON T1.T1_T2 = T1_T2.T1_T2_id

This returns the data I want from T1 and T1_T2. I want to join T1_T2 on to T1_T2_T3 like so:

SELECT * FROM T1_T2
    LEFT JOIN T1_T2_T3 
        ON T1_T2.T1_T2_T3 = T1_T2_T3.T1_T2_T3_id

Can I do this in one query?

Answer 1

I guess you are looking for something like this:

SELECT * FROM T1
    LEFT JOIN T1_T2 
     ON T1.T1_T2 = T1_T2.T1_T2_id
    LEFT JOIN T1_T2_T3 
     ON T1_T2.T1_T2_T3 = T1_T2_T3.T1_T2_T3_id