Hi Almar, all!
Almar van Pel wrote: > Hello all, > > > > I'm trying to get a TEXT field updated with its own content and an extra > string by using concat. The query looks something like this: > > > > update field_comment set field_comment = concat(field_comment, '\n > my_new_string'); > > > > I've noticed that in this case the update doesn't work when the content of > the field is empty. I tried setting up a testcase, and as long as the > textfield is NULL concat doesn't return anything. Is this 'as designed' or a > bug? Should it work as designed, would anyone know another easy way without > setting a byte first? You have not understood the concept of NULL in SQL: NULL does not mean "empty", it means "unknown". If you concat some text to an unknown text, what should the result be? It must be unknown again, as the start of the result is still unknown. In general, in SQL all operations that get (at least) one NULL operand again return NULL; the only exception that comes to my mind is the "IS NULL" predicate. Especially, the comparison of two NULL values does not return TRUE, rather it returns NULL (because it cannot be determined whether those two "unknown" operands both have the same value). So if you took NULL to represent an empty string, you made a wrong design assumption and should change it: Explicitly set those fields to empty strings ''. HTH, Jörg -- Joerg Bruehe, MySQL Build Team, joerg.bru...@oracle.com ORACLE Deutschland B.V. & Co. KG, Komturstrasse 18a, D-12099 Berlin Geschaeftsfuehrer: Juergen Kunz, Marcel v.d. Molen, Alexander v.d. Ven Amtsgericht Muenchen: HRA 95603 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
