SQL Tuning - Using DECODE

SQL Tuning - Using DECODE :
Programmers often need a way to count and/or sum variable conditions for a group of rows. The DECODE statement provides a very efficient way of doing this. Because DECODE is rather complex, few programmers take the time to learn to use this statement to full advantage. This section describes some common ways you can use DECODE to improve performance.

Using DECODE to Make Decisions
Using DECODE to Reduce Processing
Using DECODE in ORDER BY and GROUP BY Clauses
CASE Function