RE: query problem with null
Have you tried to set city = null (i.e. without the quotes)? David. -Original Message- From: Richard Reina [mailto:gatorre...@gmail.com] Sent: Friday, March 09, 2012 4:24 PM To: mysql@lists.mysql.com Subject: query problem with null When I do the following query: SELECT * FROM geo_trivia WHERE city IS NULL; certain columns that DO have 'NULL' value for city and not a '' (blank) value do not show up. I have even gone to the extent of reseting these records value as ='NULL' with UPDATE and they are still are not selected when I run the above query. Can anyone help? The information contained in this e-mail and any attached documents may be privileged, confidential and protected from disclosure. If you are not the intended recipient you may not read, copy, distribute or use this information. If you have received this communication in error, please notify the sender immediately by replying to this message and then delete it from your system. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: query problem with null
Ahhh... Thank you, that was exactly what the problem was. I will fix the code that is setting the value of these new records to 'NULL'. Thank you. 2012/3/9 David Lerer dle...@us.univision.com Have you tried to set city = null (i.e. without the quotes)? David. -Original Message- From: Richard Reina [mailto:gatorre...@gmail.com] Sent: Friday, March 09, 2012 4:24 PM To: mysql@lists.mysql.com Subject: query problem with null When I do the following query: SELECT * FROM geo_trivia WHERE city IS NULL; certain columns that DO have 'NULL' value for city and not a '' (blank) value do not show up. I have even gone to the extent of reseting these records value as ='NULL' with UPDATE and they are still are not selected when I run the above query. Can anyone help? The information contained in this e-mail and any attached documents may be privileged, confidential and protected from disclosure. If you are not the intended recipient you may not read, copy, distribute or use this information. If you have received this communication in error, please notify the sender immediately by replying to this message and then delete it from your system.
Re: query problem with null
- Original Message -
From: David Lerer dle...@us.univision.com
Have you tried to set city = null (i.e. without the quotes)?
Spot on, I'd think.
NULL values are not a string with NULL in it - that's only what it looks like
in query results :-) An empty string ('') is to strings what 0 (zero) is for
integers: it says the value of this field is nothing. NULL, on the other
hand, means the value of this field is a total unknown, which is useful, for
example, in a field 'quantity': zero is still a valid, meaningful quantity;
whereas you would use NULL to indicate that you simply do not know the quantity.
It's a bit of a peculiar concept, but as David indicated, IS NULL will not
match fields set to the string NULL - as that is a string, not an unknown.
Another funny attribute of NULL is that NULL != NULL. There simply *is* nothing
to compare, so you cannot ever say it's equal.
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