SUM

The SUM() function in SQL is used to calculate the sum of a column. This function allows you to add up a column of numbers in an SQL table.

The syntax for SUM is as follows:

SELECT SUM(column_name) FROM table_name;

Where column_name is the name of the column you want to calculate the sum of, and table_name is the name of the table where the column is.

For example, consider the following ORDER table:

|   OrderID  | Company | Quantity |
|-------------|-----------|----------|
|     1           |     A     |    30     |
|     2           |     B     |    15     |
|     3           |     A     |    20     |

If you want to find the total quantity, you can use SUM():

SELECT SUM(Quantity) AS TotalQuantity FROM Order;

Output will be:

| TotalQuantity |
|----------------|
|           65     |

Note: The SUM() function skips NULL values.

One of the common use cases of SUM() function is in conjunction with GROUP BY to get the sum for each group of rows.

Example:

SELECT Company, SUM(Quantity) AS TotalQuantity 
FROM Order 
GROUP BY Company;

This will give us the sum of Quantity for each Company in the Order table.

| Company | TotalQuantity |
|-----------|----------------|
|     A     |           50     |
|     B     |           15     |

Notably, in all databases, including MySQL, PostgreSQL, and SQLite, the SUM() function operates the same way.