Question

Here is a simple situation. (My apologies my SQL is quite rusty.)

(I am using MySQL and Java but it should not matter too much.)

Let’s say I have two tables.

Here is a simple SQL statement:

A:

insert into patient (patient_id) values (16)

Now there is another table person, which has a person_id and that has to be constrained to match patient_id.

B:

CONSTRAINT `person_id_for_patient` FOREIGN KEY (`patient_id`) REFERENCES `person` (`person_id`) ON UPDATE CASCADE)

What I am looking for is some pre-built tool, solution, etc., that might allow one to expand an insert statement such as A in order to satisfy constraints automatically.

In other words, that would automatically expand A into:

insert into person (person_id) values (16)
insert into patient (patient_id) values (16)

Any ideas?

Thank you
Misha

Answer 1

Consider these 2 solutions to handle your business logic requirements:

• Strongly suggest creating a stored procedure to insert into both the person and the patient tables.

CREATE PROCEDURE CreatePerson(IN newID int)
BEGIN
   insert into person (person_id) values (newID);
   insert into patient (patient_id) values (newID);
   --as many statements as you need. perhaps wrap in a TRANSACTION.
END;

This will help control the business logic. You’ll have to enforce that all code NOT directly insert into the person using adhoc SQL. How easy/hard this is depends on your environment.

• Create a trigger for after insert on the person table to automatically insert into patient. Creating triggers in MySQL. Triggers will definitely solve your dev problem here, but generally aren’t overall a great solution, as you tend to ‘forget’ that they’re there. Later, when you are investigating a defect/problem in your database, you may overlook the hidden logic in the trigger. Read more opinions on triggers.

Either way, with either of these two, you’ll get the creation of a record into the patient after person.

The question then becomes – does this business rule need enforcing the other way around? What happens when a process tried to write into the patient table? Does it require that a match exist in the person table?