Am 02.03.2012 13:59, schrieb Jay A. Kreibich:
On Fri, Mar 02, 2012 at 10:44:20AM +0100, Christoph P.U. Kukulies scratched on
the wall:
When defining a column TEXT PRIMARY KEY (is that possible on TEXT?),
would this imply uniqueness?
Kind of. It implies uniqueness in the SQL sense, which does not
include NULLs (remember, NULL != NULL). The SQL term "PRIMARY KEY"
should imply both "UNIQUE" and "NOT NULL", but there is a long
standing issue in SQLite that allows NULLs in non-integer PRIMARY
KEY columns. This allows "duplicate" NULL entries in a PK column.
Normally this isn't an issue, as you shouldn't have NULLs in a
single-column PK anyways.
Or would I have to write something like TEXT PRIMARY KEY UNIQUE ?
No, but to be extra safe you should write "TEXT PRIMARY KEY NOT NULL."
-j
Thanks. And thanks to others for contributing.
My logic is the following: When I'm inserting files and their respective
contents
into the database, I have to decide, whether a file is already there.
I'm building a
unique ID made up from the basename, md5sum and size of the file. This
results
as a TEXT PRIMARY KEY (e.g. filename_md5sum_size).
Can I use (I'm using System.Data.SQLite) a try clause to find out
whether the entry is
already there?
I think this can be faster than asking the database by an SQL statement,
whether
the KEY is already there.
--
Christoph
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