I tried query with subquery in where clause and found big issue for this type of subquery.

 

for example:

 

select * from orders where orders.partid in (select partners.partid from partners where partners.country = ‘Spain’)

 

Perfomance Analysis returns me this

 

partners     687660 non index reads

orders          28657 index reads

 

If you analyze this result you’ll find that there is 687659 unnecessary non index reads. If developer of optimizer accept that all queries on the left side of where clouse has priority (and there is no way to be opposite) than we have big improvement in optimization.

 

Best regards,

 

Djordje Radovanovic