SQL Getting Started Tutorial: The SQL COUNT () function tutorial

SQL COUNT () function tutorial

The count () function returns the number of rows that conform to the specified criteria.

Database count (column_name) syntax
The specified column for the quantity value returned by the COUNT (column_name) function (the null value will not be evaluated):

SELECT COUNT (column_name) from table_name

  
  

   
   

   
Database Count 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 look at an example.

 
      
      

  
       
       
 
        
 
         
_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 number of orders from "Customer Nelson".

We use the following SQL statement:
      

      
      

      

      

      
      
SELECT COUNT (Customer) as Customernilsen from Orders
WHERE customer= ' Nilsen '

      
      


      
      
       
       

        
        

        
The result of the SQL statement will be above 2 because the customer Nelson has made the 2nd order total:
        

        
        

        

        

        
        

        

        

        
        
 
         
 
          
 
           
Customernilsen
 
          
 
          
 
           
2
 
          
 
         
 
        
        
        

        

        

        
        

        

        

        
        

        
Look at an instance of SQL COUNT (*).
        

        
        

        

        

        
        
SELECT COUNT (*) as numberoforders from Orders

        
        


        
        
Output results.

        
        


        
        
 
          
          

  
           
           
 
            
 
             
Numberoforders
 
            
 
            
 
             
6
 
            
 
           
 
          
          

        
        


        
        
An instance of SQL COUNT (DISTINCT column_name).

        
        


        
        
 
          
          

  
           
           


We use the following SQL statement:
  
           
           
 
           
           
SELECT COUNT (DISTINCT Customer) as Numberofcustomers from Orders

  
           
           


  
           
           
Results.

  
           
           
   
            
            

    
             
             
 
              
 
               
Numberofcustomers
 
              
 
              
 
               
3