Number of Subqueries

Minimise 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 ...
)