Hi ! Well ... I give you an example from another world: in mathematics there are some "special values" NaN or PositiveInfinity or NegativeInfinity and more ...
If you program in Java (and other programming languages), a Float variable can have these "Special values". One MUST represent them there as values, because mathematical operations sometimes result in these ... You may ask "Are these real Values ?" and can debate and debate and both standpoints are valid ... they are "special values" but they are no "real values" you can operate with easily. So NULL ist not a value in a common sence it represents the absense of a real value of the column type ... if the column type is INTEGER and a row X value is NULL, you can NOT easily add it to another row Y value .... For example: if you have a table with 20 rows with an INTEGER column, some are null, some not, and you use the sum() function ... the NULL columns will be ignored ... BUT: NULL is a "special value", because you _CAN_ for example find null columns with the "IS NULL" expression within the WHERE clause, and for example with an Integer "column IS NULL" is different that "column = 0" If you have a Table with an Integer column where some values are NULL and some are 0 you can differentiate between them. So NULL _IS_ special, its not 0 for INTEGER's its not '' for strings ... if you want to set a value to NULL within INSERT or UPDATE you use the keyword NULL and you can have a default value of NULL ... Do you see what I mean/meant ? Ralf > Hi, > I thought I knew what a null was (with a little help from the SAP list) until >I read this. I must say I found the "special value"(see previous post's on this >thread) theory slightly vague? > http://searchdatabase.techtarget.com/tip/1,289483,sid13_gci784090,00.html > Anybody who is really clear about the whole null concept please mail me. (after >reading the above pls.) > -Ajit > _______________________________________________ > sapdb.general mailing list > [EMAIL PROTECTED] > http://listserv.sap.com/mailman/listinfo/sapdb.general > -- theCo.de AG Oranienstr. 10-11, 10997 Berlin fon +49 30 617 897-0 fax -10 [EMAIL PROTECTED] http://www.theCo.de _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
