Need help understanding left join logic (in proc sql) on multiple tables

[Sas_Act_114]

Hello all,

I am looking through a SAS program and there are several left joins written that has me scratching my head. To give a simple example, say there are three tables A, B, and C. The coding goes something like this:

Select *

From A Left Outer Join B

On A.ID1 = B.ID1

Left Outer Join C

On B.ID2 = C.ID2

This is the first time I have seen left joins set up this way. I don't know if the program is joining tables B and C and then joining that new table to A, or if it joins A and B first, and then joins C to the new combined A/B table. Any clarification on this is appreciated, thanks!

[PGStats]

In SAS/SQL these joins are performed left to right, i.e. A with B then the result joined with C. The order can be altered with parentheses.

Select *
From A Left Outer Join
(B Left Outer Join C On B.ID2 = C.ID2) as D
On A.ID1 = D.ID1;