根据另一个表的主键创建主键

Question

I have a table that looks like this (only showing a few of the columns as an example), where the ID is being auto incremented:

 ('client' table) client_id | state | concerns __________|_______|_________ 01 | MA | ... 02 | NJ | ... 03 | MA | ... 

I have another table, and what I want to do for the PK of that table is to create it based on the PK from the 'client' table. (A client can be one person, or two)

 ('person' table) person_id | fname | dob | client_id __________|_______|____________|__________ 01A | MA | 1/1/1978 | 01 01B | MA | 2/7/1985 | 01 02 | NJ | 5/17/1983 | 02 03A | MA | 3/12/1970 | 03 03B | MA | 5/23/1987 | 03 

So it will only add the letters to the PK if the client consists of two people (notice how 'person_id' stayed as 02).

How should I go about doing this? I'm not sure if having it as '01_1', '01_2' would make it easier than having it look like '01A', '01B', but whichever way makes it easiest would be preferred! Thank you in advance!

**(I forgot to mention that I'm using MySQL, if that makes a difference!)

Answer 1

You needs to create a foreign key that references to client id, and then make it a primary key. I suggest you to create others columns for specific data.

Here is a sample, I ignored others columns:

CREATE TABLE client (
    client_id CHAR(40),
    PRIMARY KEY(client_id),
) ENGINE=INNODB;

CREATE TABLE person (
    client_id CHAR(40),
    person CHAR(40),
    PRIMARY KEY (client_id, person),
    FOREIGN KEY (client_id) REFERENCES client(client_id)
) ENGINE=INNODB;