PostgreSQL COALESCE() Function

The NULL function can be used to provided alternate value of a column if it contains NULL value. In PostgreSQL, COALESCE() function allows to return an alternative value when an expression is NULL.

Example:

Consider a database table called Product with the following records:

If the OrderQuantity is optional and can contain NULL values. The statement mentioned below will give NULL value.

SELECT *, Price * (StockQuantity + OrderQuantity) AS Inventory
FROM Product;

This will produce the result as shown below:

To avoid such situations, the NULL function is used which provides alternative value to a column if it contains NULL value.

PostgreSQL COALESCE() Function

The PostgreSQL COALESCE() function lets you to provide an alternative value if column value is NULL. The statement below returns 0 if the value is NULL.

SELECT *, Price * (StockQuantity + COALESCE(OrderQuantity, 0)) AS Inventory
FROM Product;

This will produce the result as shown below: