SQL Join Table vs. Select -


i have inherited legacy sql code following snippet (i've anonymized simplicity sake).

create external table dim_abc (user_id int)  create table dim_foo select user_id,        ... my_table join (select * dim_abc) b on (a.user_id = b.user_id)

instead of...

from my_table join dim_abc b on (a.user_id = b.user_id)

any idea why previous developer have done select within join?

** code hive.

the version without subselect better variety of reasons. databases (you don't mention database) lose ability use indexes on dim_abc because of subquery.

that not question, though. best guess code started out more complicated. dim_abc might have required logic @ 1 point in time. code simplified, end result useless subquery in from clause. guess, offers 1 plausible scenario.


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