In this entry i will explain the effect of null records in not equal statements.Basically null records omitted by not equal statement and Oracle shows us missing resultset.
Step1: Here below our department table which contains department_names and some rows have null department names.
Step2: Here following resultset shows us only 24 records which it should be 26
( null records are filtered by the statement plus with the row which department name 'Marketing')
Step3: To fix this sql statement can be typed as below. ( which we get 26 records )