|
|
Posted by meltedown on 06/03/06 00:13
Malcolm Dew-Jones wrote:
> meltedown (groups2@reenie.org) wrote:
> : This is probably a stupid question but I don't get it.
> : I have a table called sites
>
> : 2 rows have a name='siteisdown'
> : 1 row has a value of 1 and the other has a value of '' (nothing)
>
> : This works fine, it returns 1 row with a value of 1, along with all the
> : other columns.
> : "SELECT * from sites where name='siteisdown' AND value =".TRUE);
>
> ?
>
> : This returns nothing:
> : "SELECT * from sites where name='siteisdown' AND value ='' ";
>
> Try the syntax
>
> SELECT * from sites where name='siteisdown' AND value is NULL;
>
>
> The database is probably one that uses '' as a shorthand for the NULL
> value. NULL is a special value that represents having no value or a value
> which is unknown. There aren't any values that can ever be equal "no
> value", and so value='' selects nothing.
>
> As an aside, you'll note that "NULL = NULL" will also return no rows.
> That is because NULL also represents an "unknown" value, and it isn't
> possible to say that two unknown values are the same as each other (since
> you don't know what values they are).
>
OK thanks, I had tried that but my syntax was wrong. I used php null
instead of sql null
"SELECT * from sites where name='siteisdown' AND value is ".NULL"
which of course doesn't compute.
Navigation:
[Reply to this message]
|