On Tue, Jul 15, 2003 at 04:36:24AM -0700, Alan Mead wrote: > > --- James Mills <[EMAIL PROTECTED]> wrote: > > > Just reconfirming with you and solidifying my knowledge. > > The reason it returns "" is because: when working with > > native pascal types, assigning null to a string results > > in an empty string "" right ? > > > > cheers > > James > > James, > > Pascal is a strongly typed language and there is no Pascal string > precisely equivalent to a NULL. Someone (either the SQLite authors > or the one who wrote the Pascal wrapper) decided to automatically > translate NULL into empty (zero-length) strings. And it's impossible > now to distinguish actual null values from fields containing actual > zero-length strings.
I think I'm slowly understanding this bit now. I don't claim to be an SQL expert. But SQL (sqlite anyway) is capable of storing any data types, strings, integers, boolean etc, including NULL values. I hope I'm correct here... I don't believe the authors of the sqlite unit do translate NULL into empty (zero-length) strings. I did check the source, check yourself if I'm wrong. Why could I not simply check for '""' in my sql return functions and simply return '' instead (a pascal empty string) ? Would this be terribly wrong ? Or am I still going to have to follow Michael's suggestion in finding a TDataset desendant ? (I don't understand what a TDataset desendant really is and why I need to use one but anyway...) > > You could solve this in several ways: > > 1) re-write all the code to return and store a more complex record > (as suggested in a previous post) that include a string and a > boolean, this record completely and precisely captures the data SQL > is returning; > > 2) re-write the code that does the automatic translation to insert > the string 'NULL' (in which case, you will never be able to > distinguish NULL's from actual fields containing the value > 'NULL'--but maybe this is no problem); > > 3) you could simply avoid ever having empty strings in your database > (in which case, empty strings returned are always NULL's) There should be no empty string in my database anyway. If a field is empty it's value is NULL. > > 4) Live with not being able to distinguish, in many instances, an > empty string is practically the same as a NULL (in other instances, > however, it indicates that some records in a full join failed to find > a match) cheers James > > HTH, > > -Alan > > __________________________________ > Do you Yahoo!? > SBC Yahoo! DSL - Now only $29.95 per month! > http://sbc.yahoo.com > > _______________________________________________ > fpc-pascal maillist - [EMAIL PROTECTED] > http://lists.freepascal.org/mailman/listinfo/fpc-pascal -- - - James Mills Zero Defect Software Engineers Group - ZDSEG _______________________________________________ fpc-pascal maillist - [EMAIL PROTECTED] http://lists.freepascal.org/mailman/listinfo/fpc-pascal
