SQL - 'COUNT' with 'DISTINCT'

Consider you have an employee table which contains the following records:

Select * from emp

empname	empid	sal	mgr_id
sundar	101	100	505
sund1	102	100	506
sund2	103	10	507
sund3	104	1000	103
sund4	105	2000	509
Sundar1	NULL	NULL	NULL
Sundar2	NULL	NULL	NULL

And of course, you very well knew that count(*) returns the number of records in a table.

For example: Select count(*) from emp .

It returns ‘7’

Suppose if you want to get the Unique number of records in a column of table, you may use distinct.

Select distinct(empid) from emp

But problem here is that, distinct consider ‘Null’ values as well. So it returns below 6 records.

empid

101

102

103

104

105

NULL

The best way to find out the unique records in a particular column, use 'count' instead of 'distinct'.

For example:

Select count(empid) from emp

It returns ‘5’ and ignores ‘Null’ values.