SQL COUNT(), AVG(), and SUM() functions are aggregate functions used in SQL queries to perform calculations on groups of data or columns in a database table. Here's a brief overview of each function:
COUNT(): The COUNT() function is used
to count the number of rows or records in a database table or a result set of a
query. It can be used with or without an argument, depending on what you want
to count. Here are some examples:
a.
SELECT COUNT(*) FROM users; -- Count all rows in the users
table
b.
SELECT COUNT(id) FROM
orders;
-- Count the number of non-null values in the id
column of the orders table
c.
SELECT COUNT(DISTINCT city) FROM
customers; --
Count the number of distinct values in the city column of the customers table
AVG(): The AVG() function is used to calculate the average or mean value of a column in a database table or a result set of a query. It can be used with a numerical column as an argument. Here's an example:
· SELECT AVG(price) FROM products; -- Calculate the average
value of the price column in the products table
SUM(): The SUM() function is used to
calculate the sum of values in a column in a database table or a result set of
a query. It can be used with a numerical column as an argument. Here's an
example:
· SELECT SUM(quantity) FROM orders; -- Calculate the sum of
the quantity column in the orders table
These functions are often used in
combination with other SQL statements, such as SELECT, WHERE, GROUP BY, and
HAVING, to perform more complex calculations and retrieve specific information
from the database. It's important to understand how these aggregate functions
work and how to use them effectively in your SQL queries to retrieve and
manipulate data from a database table. Additionally, it's worth noting that
these aggregate functions may behave differently depending on the database
management system you are using, so be sure to refer to the documentation of
your specific database system for accurate usage and syntax.
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