Question

We are developing ETL jobs and our consultant has been using “old style” SQL when joining tables

select a.attr1, b.attr1
from table1 a, table2 b
where a.attr2 = b.attr2

instead of using the inner join clause

select a.attr1, b.attr1
from table1 as a inner join table2 as b
   on a.attr2 = b.attr2

My question is that in the long run, is there a risk for using the old “where join”? How long this kind of joins are supported and kept as ANSI standard? Our platform is SQL Server and my primary cause is that in the future these “where joins” are no longer supported. When this happens, we have to modify all our ETL jobs using “inner join” style of joins.

Answer 1

I doubt that “where joins” would ever be unsupported. It’s just not possible to not support them, because they are based on Cartesian products and simple filtering. They actually aren’t joins.

But there are many reasons to use the newer join syntax. Among others:

• Readability
• Maintainability
• Easier change to outer joins