Number of Subqueries

Minimize the number of subqueries in SQL statements.

Example:

Rewrite an SQL statement like the following:

SELECT    ...

FROM      Table1

WHERE     ColA =

(

          SELECT   T2.ColA     

          FROM     Table2 T2

          WHERE ...

)

AND       ColB =

(

          SELECT   T2.ColB 

          FROM     Table2 T2

          WHERE ...

)

to:

SELECT    ...

FROM      Table1

WHERE     (ColA, ColB) =

(

          SELECT    T2.ColA

          ,         T2.ColB

          FROM      Table2 T2

          WHERE ...

)