maria-discuss team mailing list archive

[Pantelis Theodosiou <ypercube@xxxxxxxxx>]

On Mon, Apr 4, 2016 at 2:10 PM, Peter Laursen <peter_laursen@xxxxxxxxxx>
wrote:

> As described in this Blog
> http://mablomy.blogspot.dk/2016/04/check-constraint-for-mysql-not-null-on.html.
> A very nice hack/trick IMO.
>
> However it is not working with MariaDB as VC's cannot be declared NOT
> NULL.  What prevents that?
>
>
(Peter, sorry fro the previous private reply, not sure how I got the reply
buttons wrong.)

I can't answer that, but there's another workaround for (some) CHECK
constraints, described here:
http://dba.stackexchange.com/questions/9662/check-constraint-does-not-work/22019#22019

Unfortunately, it works only for smallish (int or date) ranges. We can't
use for floats or decimals (as it would require a very big reference table).

But it could be combined with the hack you link, using something like:


CREATE TABLE truth (t BOOLEAN PRIMARY KEY) ;
INSERT INTO truth (t) VALUES (TRUE) ;
-- and remove all write permissions to the table

CREATE TABLE checker (
    i int,
    i_must_be_between_7_and_12 BOOLEAN
         AS (IF(i BETWEEN 7 AND 12, TRUE, FALSE))
         PERSISTENT,
    CONSTRAINT check_i_must_be_between_7_and_12
    FOREIGN KEY (i_must_be_between_7_and_12)
      REFERENCES truth (t)
    );


Haven't tested it but should work for more complex constraints as well.

Pantelis