I suspect you want 'IS NULL' rather than '= NULL'. :) I always find it best to think of NULL as "undefined value" rather than "no value" - which is why you need to check for it especially (using IS rather than = or other operators).
Cheers, Matt > -----Original Message----- > From: Yonah Russ [mailto:[EMAIL PROTECTED] > Sent: 21 April 2004 14:47 > To: MySQL List > Subject: Re: query help > > I got a response off the list suggesting writing a function to go over > the query results- it's not hard but I'd rather do this in sql if > possible. > > I came up with this: > select books.bookid,books.title,copies.copyid from books left join > copies on books.bookid=copies.bookid where copies.copyid=NULL; > > this didn't work even though without the where clause I got exactly what > I wanted- the left join filled in the entries that didn't have copies > with a null copyid. > > what did I do wrong? > thanks > yonah > > Yonah Russ wrote: > > > Hi, > > I have two tables- books and copies > > > > every book has an id in the books table > > every copy of a book has the books id and a copy id in the copies > > table (1 row per copy) > > > > I want a list of all the books that don't have any copies meaning all > > the book id's in books that don't match any book id's in copies. > > > > how can I do this? > > thanks > > yonah > > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
