How to add many constrains to a mysql database - mysql

Question

I am trying to set up a MySQL database. The final database will consist of approx. 200 columns distributed over 7 tables. Now I’ve got the problem that I’d like to add check constraints to most of the columns. Some columns will only have one constraint, others will have many and/or are affected by columns of different tables.
E.g. rows can only be added to a table if the age is older than 20 years or if the zip code consists of 5 characters and starts with 1 or if the admission date (in table admission) is before the discharge date (in table discharge).
Just three examples. I can think of 1000 more, which is my problem.
I’d like to add these constraints in a more structured way. A trigger with more than 10 constraints will be complex and no one, except for the author will be able to reconstruct all constraints. But if the database will be used for years, many administrators will have to work with the database and maybe add new or remove unnecessary constraints.
DELIMITER $$
CREATE TRIGGER `test``_before_insert` BEFORE INSERT ON `zip`
FOR EACH ROW
BEGIN
IF NEW.zip_id < 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint 1';
END IF;
IF NEW.zip_id = 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint 2';
END IF;
END $$
DELIMITER ;
That's the way I don't want to handle the problem. 
My question is, if there is a way to declare constraints in a normal-human-readable-way (e.g. one constrain with a nice name per textfile) and add these to the database.

Answer 1

Unfortunately, the check constraint in MySQL does not work. You can learn more at this SO question. Even the accepted answer for this question suggests the use of triggers.
You are on the right track when you decided to use triggers. However you have a few misconceptions.
A trigger is basically defined on an event on a table. As you have 7 tables, you will have 7 separate triggers per table, at least. Read more about triggers in MySQL at MySQL Reference Manual.
It is you and you only that has to find ways to keep the code well organized so that your teammates and even you can understand it well. Everything that you need to do is follow the best practices followed across the software industry. For a few hints you can refer here and here on dba.stackexchange.com.

Answer 2

I have thought about my problem over, and have another argument and solution about the checking of constrains in a trigger.
First, the argument: I probably need at least a BEFORE INSERT and a BEFORE UPDATE trigger to check my data. Both triggers are more or less identical. If a constrain changes over time, I have to submit the change to both triggers or my data can be come inconsistent.
I thought of stored procedures to implement one constrain, which can be called in the INSERT and UPDATE trigger. Now If I change a procedure, it affects both triggers.
DROP TRIGGER IF EXISTS test_before_insert;
DROP PROCEDURE IF EXISTS `procedureLess5`;
DROP PROCEDURE IF EXISTS `procedureEquals5`;
DELIMITER $$
CREATE PROCEDURE `procedureLess5` (IN myInput INT)
BEGIN
IF myInput < 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint 1';
END IF;
END $$
CREATE PROCEDURE `procedureEquals5` (IN myInput INT)
BEGIN
IF myInput = 5 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT = 'check constraint 2';
END IF;
END $$
CREATE TRIGGER `test_before_insert` BEFORE INSERT ON `zip`
FOR EACH ROW
BEGIN
CALL procedureLess5(NEW.zip_id);
CALL procedureEquals5(NEW.zip_id);
END $$
DELIMITER ;
Is this an opportunity?
How about the performance of my database if I have more than 20 called procedures?
Or do you think of another way? I’m not fixed to MySQL, PostgreSQL is also an opportunity. Is it better/faster/more standard to use CHECK CONSTRAINS in PostgreSQL?