SQL Server COUNT function

SQL Server COUNT function

 SQL Server COUNT function returns number of items in a group.

COUNT(*) -> returns number of rows in the table

COUNT(col) -> returns non-null values count

COUNT(distinct col)-> returns non-null unique values from the column.

Count(Sal) on Emp table

EMPNO	ENAME	JOB	MGR	HIREDATE	SAL	COMM	DEPTNO
7369	SMITH	CLERK	7902	12/17/1980 12:00:00 AM	800.00		20
7499	ALLEN	SALESMAN	7698	2/20/1981 12:00:00 AM	1600.00	300.00	30
7521	WARD	SALESMAN	7698	2/22/1981 12:00:00 AM	1250.00	500.00	30
7566	JONES	MANAGER	7839	4/2/1981 12:00:00 AM	2975.00	300.00	20
7654	MARTIN	SALESMAN	7698	9/28/1981 12:00:00 AM	1250.00	1400.00	30
7698	BLAKE	MANAGER	7839	5/1/1981 12:00:00 AM	2850.00		30
7782	CLARK	MANAGER	7839	6/9/1981 12:00:00 AM	2450.00		10
7839	KING	PRESIDENT		11/17/1981 12:00:00 AM	5000.00		10
7844	TURNER	SALESMAN	7698	9/8/1981 12:00:00 AM	1500.00	0.00	30
7900	JAMES	CLERK	7698	12/3/1981 12:00:00 AM	950.00		30
7902	FORD	ANALYST	7566	12/3/1981 12:00:00 AM	3000.00		20
7934	MILLER	CLERK	7782	1/23/1982 12:00:00 AM	1300.00		10

Query:  Select number of records in the table emp
    
             select count(*) from emp;
O/P:
         12

         select count(*) as "Number of Records"  from emp;

O/P:       
            "Number of Records"
             800.00

Query: Select employee count of Dept No 10:

select count(*)  from emp where deptno=10;

O/P: 3


Query: Get  number of comm entries in the emp table

select count(comm)  from emp

O/P :5

 

select count(distinct comm)  from emp
O/P :4

 

 

Note: count(columnname) returns non-null  values.  count(distinct columnname) returns number of non-null unique values.




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