nested query vs jOINs

Question

whos could be much efficient if I use nestted subquery, JOINs Or maybe temp tables .. another question : in subqueries if i use IN Cl

Answer 1

First, your syntax is probably incorrect.Thus, the two formats would look like:

Select ...
From X 
Where Exists( Select 1  From Y Where Idx = Y.SomeColumn ) 
    Or Exists( Select 1 From Y Idy = Y.SomeColumn )

And

With XX As
    (
    Select ...
    From Y
    )
Select ...
From X
Where Exists ( Select 1 From XX Where Idx = XX.SomeColumn )
    Or Exists ( Select 1 From XX Where Idy = XX.SomeColumn )

Note the Exists statements. They are not Where Col Exists(... but instead are just Where Exists( ....

Second, the efficiency and speed will depend on the data, statistics, indexes and, at the end of the day, what the optimizer is able to make more efficient. Thus, you really need to look at the execution plan to know which is faster. Now, another form might be:

Select ...
From X 
Where Exists    (
                Select 1  
                From Y 
                Where Idx = Y.SomeColumn 
                Union All
                Select 1
                From Y
                Where Idy = Y.SomeColumn
                )