[Tutor] String representation of NULL (non type) values

[Peter Otten]

Ulrich Goebel wrote:

> Hallo,
> 
> from a SQLite database I get a value by SELECT s from... which normaly
> is a string, but can be the NULL value, wich means it is not defined. To
> put the value into a form (made by QT) I need a string representation.
> 
> str(s) gives either the string itself (which is good) or "None" (which
> is not so good) in the case of NULL. Instead of "None" I would prefer an
> empty string "". How to get that?
> 
> Possibly there is a build in function smart(s1, s2, s3,...) which
> returns the first s which is a useable string, or even "" if there isn't
> any string in the arguments?

coalesce(arg1, arg2, arg3, ...)

returns the first non-NULL argument; you'll get the empty string by 
providing it as the last argument:

>>> db = sqlite3.connect(":memory:")
>>> cs = db.cursor()
>>> next(cs.execute("select coalesce('could be a field', '');"))
(u'could be a field',)
>>> next(cs.execute("select coalesce(NULL, '');"))
(u'',)

See 

http://sqlite.org/lang_corefunc.html