COUNT function in SQL Server

This article will show you in detail how to use functions that handle COUNT () numbers in SQL Server with specific syntax and examples to better visualize and capture functions.

Describe

The COUNT function in SQL Server is used to count the number of records (data, rows) contained in a data table. The values ​​NULL omitted do not count.

Syntax

To use the COUNT function in SQL Server, we use the following syntax:

 SELECT COUNT(cot) 
 FROM bang 
 [WHERE dieukien]; 

Parameters :

1. cot: column or calculated value, the expression you want to count
2. state: the table used to retrieve the record. Must have at least 1 table in the FROM clause.
3. dieukien: optional. Conditions that the record must meet to be selected.

Note :

1. The COUNT function can be used in later versions of SQL Server: SQL Server 2017, SQL Server 2016, SQL Server 2014, SQL Server 2012, SQL Server 2008 R2, SQL Server 2008, and SQL Server 2005.

For example

Take a look and explore some examples of COUNT functions in SQL Server.

Suppose, we have the following data table:

Example 1: Count the number of categories in the table

 SELECT COUNT(*) 
 FROM Quantrimang 
 WHERE Sobai > 100; 
 
 Result: 5 

In this example we count the number of categories in the Quantrimang table that are larger than 100.

Example 2: Use DISTINCT

The DISTINCT and COUNT commands can be used together to count the number of duplicate results.

 SELECT COUNT(DISTINCT Sobai) 
 FROM Quantrimang 
 WHERE Sobai > 100; 
 
 Result: 4 

This example uses the keyword DISTINCT, so the repeated values ​​are counted only once. In the given data table, the value '101' appears twice, but only once, so the total number of calculated lines will be 4.

Example 3: Using GROUP BY

The following example counts all records related to a large section and you will do the following:

 SELECT Chuyenmuclon, COUNT(Chuyenmuccon) AS "So luong" 
 FROM Quantrimang 
 GROUP BY Chuyenmuclon; 
 
 Result: 
 Chuyenmuclon So luong 
 Laptrinh 3 
 Mang xa hoi 2 
 Trinh duyet web 1 

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