# 100 Days of SQL

## Day 12 – SQL COUNT(), AVG() and SUM() Functions

In SQL, the `COUNT()`, `AVG()`, and `SUM()` functions are used to retrieve summary information about data in a table. These functions are often used in combination with the `SELECT` statement to calculate totals, averages, and counts.

1. `COUNT()` function: The `COUNT()` function returns the number of rows that match a specified condition. The basic syntax is as follows:
``````
SELECT COUNT(*) FROM table_name WHERE condition;

``````

Here, `*` indicates that all rows in the table should be counted, and `condition` specifies the criteria for the rows to be included in the count.

For example, suppose you have a table called `customers` with columns `customer_id`, `first_name`, `last_name`, and `email_address`. If you want to count the number of customers in the table, you would use the following SQL statement:

``````
SELECT COUNT(*) FROM customers;

``````

This statement will return the total number of rows in the `customers` table.

1. `AVG()` function: The `AVG()` function returns the average value of a numeric column in a table. The basic syntax is as follows:
``````
SELECT AVG(column_name) FROM table_name WHERE condition;

``````

Here, `column_name` is the name of the numeric column for which you want to calculate the average, and `condition` specifies the criteria for the rows to be included in the calculation.

For example, suppose you have a table called `sales` with columns `product_name` and `sales_amount`. If you want to find the average sales amount for all products, you would use the following SQL statement:

``````
SELECT AVG(sales_amount) FROM sales;

``````

This statement will return the average sales amount for all products in the `sales` table.

1. `SUM()` function: The `SUM()` function returns the sum of the values in a numeric column in a table. The basic syntax is as follows:
``````
SELECT SUM(column_name) FROM table_name WHERE condition;

``````

Here, `column_name` is the name of the numeric column for which you want to calculate the sum, and `condition` specifies the criteria for the rows to be included in the calculation.

For example, suppose you have a table called `sales` with columns `product_name` and `sales_amount`. If you want to find the total sales amount for all products, you would use the following SQL statement:

``````
SELECT SUM(sales_amount) FROM sales;

``````

This statement will return the total sales amount for all products in the `sales` table.