Subject Re: Table level
From Ronnie MacGregor <No_Sp@m.Thanks>
Date Sun, 30 Sep 2018 12:50:00 +0100
Newsgroups dbase.getting-started

In article <PpvS8x#VUHA.1828@ip-AC1E04A7>, says...

> logical fields will default to false

But this is not a good thing, because it looks as if we know for sure that the
value of this field is false.

A logical field hsa three states, true, false, and unknown or undetermined.

This is really important.

Real world example . . .

We have a logical field which indicates whether or not a Patient is Diabetic.

If we have used autonullfields to default to false, then it looks as if we know
that this Patient is not Diabetic, when in fact we don't know.

In a MySQL table, we use a one character long character field for logical
purposes. This single character field can contain "T", "F", or "U" or NULL

A field value of NULL means that a user has never saved data to this field, and
is therefore treated as "U" - Unknown.

In some cases we this field defaulting to "U" on the creation of a new record.

For display purposes, the content of this type of field is often morphed :

T - "True" or "Yes"
F - "False" or "No"
U - "Unknown" or "Undetermined"
NULL - "Unknown" or "Undetermined"

Now I need to go and do something useful !!

Ronnie MacGregor

Ronnie at
dot co dot uk