SQL COUNT function

COUNT function returns the total number from the expression. It is an example of aggregate functions.

Syntax:

1. select count(column_name) from table_name;
2. select count(*) from table_name;

Count(*) returns total number of rows.
Count(column_name) returns total number of rows have data. ie it ignores null columns.

Examples:-

Consider below EMP table structure

Empno Empname Manager Deptno 10 Bill 5 11 Solomon Bill 5 12 Susan Bill 5 13 Wendy Solomon 1 14 Benjamin Solomon 1 15 Tom Solomon 1 16 Henry Solomon 2 17 Robert Susan 2 18 Paul Solomon 2

1. Find the number of employees.

select count(*) from EMP;     

COUNT(*)

----------------

   9

2. Find the total number of managers.

select count(manager) from EMP;     

COUNT(MANAGER)

----------------

   8

3. Find all managers handling more than one employees.

select manager ,count(*) from EMP group by manager having count(*) > 1;

MANAGER  COUNT(*)
------------------ ----------
Bill                    2
Solomon         5

4. Find total number of managers.

select count(distinct manager) from EMP;

COUNT(DISTINCTMANAGER)
--------------------------------------------
    3

Related topics
AVG function
MAX Function