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
|
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
—————— ———-
Bill 2
Solomon 5
4. Find total number of managers.
select count(distinct manager) from EMP;
COUNT(DISTINCTMANAGER)
——————————————–
3
——————————————–
3
