We are making some performance measurements, we are trying to determine query execution behavior. Lets say we have 4
tablesT1, T2, T3 and T4
and the query has the form:
select * from T1, T2, T3, T4 where (T1.a = T2.b and T2.c = T3.dT3.e = T4.f)
where a,b,c,d,e,f are properties of the respective tables.
Lets say that the cost based optimizer determines that the order of the joins should be T1.a=T2.b followed by T2.c =
T3.dfollowed by T3.e = T4.f
the question we have is during query execution are the joins evaluated completely one by one in that order, or the
firstjoin is evaluated completely and generates an intermediate table which is then utilized to perform the next
join....thismeans that for such a query we will need space for all the intermediate tables, which if they are very
largetables as they are in our case can significantly alter the cost of the operations...
thanks
-Ashish