Use Decode and Sign function together

Decode statements are useful in queries to a large extent. Sometimes people write the PLSQL code to achieve somethings that are possible through a normal decode statement.

For e.g. the requirement is to add two columns retrieved from the table and if its less than zero, make it zero and if its greater than zero, provide the sum of the two values as the output. This can be done using the decode statement

select column1 , coulmn2, column1+column2 ,
decode(SIGN(column1+column2), -1, 0, (column1+column2))
from tableA

The above query means that if the sum of column1 and column2 value is less than zero, then output the value as zero and if its greater than zero, output the sum as the value. We had to use SIGN function as decode does not support checks like less than or greater than.