Question

I am downloading data from a 3rd party datasource and one field is a contact’s birthday, which may be blank i.e. 0000-00-00. My users have the option of entering the contact’s birthday if they choose, and I hold this is in a separate table because if I updated the original table, whenever the user refreshed with the original datasource, all updated birthdays would be erased.

I now want to find all birthdays in next 30 days. This works on the first (original datasource) table:

    $BirthdayResults = mysql_query("SELECT * FROM Connections WHERE UserID='$UserID' AND (DATE_FORMAT(ContactBirthday, '%m%d') BETWEEN '$sCurrentDate' AND '$sDateOneMonthAdded')");    

So I am wondering if mySQL can handle this type of logic:

$BirthdayResults = mysql_query("SELECT * FROM Connections WHERE UserID='$UserID'... 
 AND IF ContactBirthday IN Connections = '0000-00-00' 
 CHECK OTHER_BIRTHDAY_TABLE AND USE THIS BIRTHDAY IF IT EXISTS 
 WHERE Connections.ContactID=OTHER_BIRTHDAY_TABLE.ContactID

Answer 1

SELECT *
FROM   Connections LEFT JOIN OTHER_BIRTHDAY_TABLE USING(ContactID)
WHERE  UserID='$UserID'
   AND DATE_FORMAT(
         IF(
           Connections.ContactBirthday = '0000-00-00',
           OTHER_BIRTHDAY_TABLE.BIRTHDAY,
           Connections.ContactBirthday
         ),
         '%m%d'
       ) BETWEEN '$sCurrentDate' AND '$sDateOneMonthAdded'

However, NULL would be more appropriate than 0000-00-00 in this situation; in which case one could use MySQL’s IFNULL() or COALESCE() functions instead:

       DATE_FORMAT(
         IFNULL(Connections.ContactBirthday, OTHER_BIRTHDAY_TABLE.BIRTHDAY),
         '%m%d'
       )