SQL getting started Tutorial: SQL COUNT () function tutorial

SQL COUNT () function tutorial

The number of rows returned by the COUNT () function meets the specified criteria.

Database count (column_name) syntax
The number value returned by the COUNT (column_name) function (null values are not calculated) in the specified column:

SELECT COUNT(column_name) FROM table_name

Database COUNT (*) syntax
The COUNT (*) function returns the number of records in a table:
SELECT COUNT(*) FROM table_name
SQL COUNT (DISTINCT column_name) Syntax
The COUNT (DISTINCT column_name
 
SELECT COUNT(DISTINCT column_name) FROM table_name
 
Let's see an instance.
 
   

    

     

      
_Id
      
OrderDate
      
OrderPrice
      
Customer
     
     

      
1
      
2008/11/12
      
1000
      
Hansen
     
     

      
2
      
2008/10/23
      
1600
      
Nilsen
     
     

      
3
      
2008/09/02
      
700
      
Hansen
     
     

      
4
      
2008/09/03
      
300
      
Hansen
     
     

      
5
      
2008/08/30
      
2000
      
Jensen
     
     

      
6
      
2008/10/04
      
100
      
Nilsen
     
    
   
 
Now, we want to count the order quantity from "customer Nielsen ".

The following SQL statement is used:
 
SELECT COUNT(Customer) AS CustomerNilsen FROM OrdersWHERE Customer='Nilsen'
 
The SQL statement returns the above 2 because the customer Nielsen has obtained 2nd orders:
 

    

     

      

       
CustomerNilsen
      
      

       
2
      
     
    
 
Here is an SQL COUNT (*) instance.
 
SELECT COUNT(*) AS NumberOfOrders FROM Orders
 
Output result.
 
     

      

       

        
NumberOfOrders
       
       

        
6
       
      
     
 
SQL COUNT (DISTINCT column_name) instance.
 
Now, we want to count some unique customers in the "order" table.

The following SQL statement is used:
 
SELECT COUNT(DISTINCT Customer) AS NumberOfCustomers FROM Orders
 
Result.
      

       

        

         
NumberOfCustomers
        
        

         
3