You have a data set that contains first name values:

FIRST_NAME	CONT(*)
LYNN	1
CYNTHIA	1
KEVIN	1
LESLIE	1
JOHN	1
JEAN	1

You create a masking rule with the following values in the Mask rule action:

Table Name	Column Name	Masking Function
.*EMPLOYEE.*	.*NAME.*	substr(\(col),1,2)||'****'

You send a SELECT query to the database:

SELECT FIRST_NAME,count(*) from EMPLOYEE group by FIRST_NAME

The following data set is an example of masked data that Dynamic Data Masking might return if you do not select the

Keep original number of rows

checkbox:

FIRST_NAME	CONT(*)
J****	2
K****	1
L****	2
C****	1

The masked output does not have the same number of rows as the original data set.

The following data set is an example of masked data that Dynamic Data Masking returns if you select the

Keep original number of rows

checkbox:

FIRST_NAME	CONT(*)
L****	1
C****	1
K****	1
L****	1
J****	1
J****	1

The masked output has the same number of rows as the original data set.