Today I discovered the SQL function ‘COALESCE’. The function returns the value with the highest precedence datatype from a comma separated list of expressions. For example:
LEFT JOIN settings ON settings.id = site_settings.setting_id
In the above example the first non NULL value passed to the COALESCE function is selected. if site_settings.value is NULL then settings.value will be selected. If settings.value is NULL, then the site_settings.value will be selected. If both values are NULL, then NULL will be returned.
Here is the MySQL reference page for the function: COALESCE
Worth keeping in mind. Came in handy for simplifying some SQL at work.