Would this be good to be added in the documentation of VIRTUAL columns?

Or as a separate page, as a way to enforce/emulate arbitrary CHECK constraints?

It can be slightly simplified (IF is not needed) and the BOOLEAN could be BIT (not sure if that adds any complication):

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

CREATE TABLE checker ( i float, i_must_be_between_7_and_12 BIT AS (i BETWEEN 7 AND 12) -- whatever CHECK constraint we want here PERSISTENT, CONSTRAINT check_i_must_be_between_7_and_12 FOREIGN KEY (i_must_be_between_7_and_12) REFERENCES truth (t) );

On Wed, Apr 6, 2016 at 6:46 PM, Pantelis Theodosiou ypercube@gmail.com wrote:

On Mon, Apr 4, 2016 at 2:10 PM, Peter Laursen peter_laursen@webyog.com 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

My suggestion is for documenting existing functionality and a use case for VIRTUAL columns.

When CHECK constraints are actually added, it will be obsolete of course but still useful for those that use older versions (5, 10).

On Sun, Oct 16, 2016 at 3:51 PM, Peter Laursen peter_laursen@webyog.com wrote:

Didn't CHECK CONSTRAINTS get introduced in MySQL 8? Then better port it from there into MariaDB I think. -- Peter

On Sun, Oct 16, 2016 at 4:45 PM, Pantelis Theodosiou ypercube@gmail.com

wrote:

...

Would this be good to be added in the documentation of VIRTUAL columns?

Or as a separate page, as a way to enforce/emulate arbitrary CHECK constraints?

It can be slightly simplified (IF is not needed) and the BOOLEAN could be BIT (not sure if that adds any complication):

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

CREATE TABLE checker ( i float, i_must_be_between_7_and_12 BIT AS (i BETWEEN 7 AND 12) -- whatever CHECK constraint we want here PERSISTENT, CONSTRAINT check_i_must_be_between_7_and_12 FOREIGN KEY (i_must_be_between_7_and_12) REFERENCES truth (t) );

On Wed, Apr 6, 2016 at 6:46 PM, Pantelis Theodosiou ypercube@gmail.com wrote:

...

ok .. I should have checked properly! :-(

On Sun, Oct 16, 2016 at 6:15 PM, Sergei Golubchik serg@mariadb.org wrote:

Hi, Peter!

On Oct 16, Peter Laursen wrote:

...

Didn't CHECK CONSTRAINTS get introduced in MySQL 8? Then better port it from there into MariaDB I think. -- Peter

I'm afraid you've got it backwards :)

MySQL 8.0 has no CHECK constraint (at least it's not mentioned in http://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-0.html).

MariaDB has it (https://mariadb.com/kb/en/mariadb/constraint/) since July 4th.

Regards, Sergei Chief Architect MariaDB and security@mariadb.org