[TransWarp] Topics for tomorrow, and beyond

alexander smishlajev alex at ank-sia.com
Thu Oct 16 03:53:21 EDT 2003

Phillip J. Eby wrote, at 16.10.2003 7:30:
> Note that the exists join can be emulated via an outer join, combined 
> with an assertion that the columns on the target are not null.

sorry, i do not understand why do you need an outer join here.  this is 
exactly what a normal, inner join does.

'exists' differ from joins (both inner and outer) in that it does not 
make a production of the "select" table and "exists" table.  if you are 
going to emulate 'exists' with a join, you will probably have to 
aggregate rows in the join result, won't you?

> Plus, don't forget UNION...  perhaps INTERSECT and DIFFERENCE as well.  
> We don't use these right now because Sybase didn't do them years ago, 
> but there were times that I really wanted them...

just curious: what intersect is needed for?

since outer joins appeared, i don't remember if i ever had a real need 
in union, and i've never used intersect or difference, although i think 
i can imagine how difference may be useful if we don't have outer joins.

best wishes,

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