PostgreSQL ISNULL

SQL Server supports ISNULL function that replaces NULL with a specified replacement value:

ISNULL(expression, replacement)

If the expression is NULL, then the ISNULL function returns the replacement. Otherwise, it returns the result of the expression.

PostgreSQL does not have the ISNULL function. However, you can use the COALESCE function which provides similar functionality. Note that the COALESCE function returns the first non-null argument, so the following syntax has a similar effect as the ISNULL function above:

COALESCE(expression,replacement)

For the COALESCE example, check it out the COALESCE function tutorial.

In addition to COALESCE function, you can use the CASE expression:

SELECT 
    CASE WHEN expression IS NULL 
            THEN replacement 
            ELSE expression 
    END AS column_alias;
Code language: PHP (php)

Check it out the CASE expression tutorial for more information.