Question

I’m working on a MySQL database that contains persons. My problem is that, (I will simplify to make my point):

I have three tables:

Persons(id int, birthdate date)
PersonsLastNames(id int, lastname varchar(30))
PersonsFirstNames(id int, firstname varchar(30))

The id is the common key. There are separate tables for last names and first names because a single person can have many first names and many last names.

I want to make a query that returns all persons with, let’s say, one last name. If I go with

select birthdate, lastname, firstname from Persons, PersonsLastNames,
PersonsFirstNames where Persons.id = PersonsLastNames.id and
Persons.id = PersonsFirstNames.id and lastName = 'Anderson'

I end up with a table like

1/1/1970 Anderson Steven //Person 1
1/1/1970 Anderson David  //Still Person 1
2/2/1980 Smith Adam      //Person 2
3/3/1990 Taylor Ed       //Person 3

When presenting this, I would like to have

1/1/1970 Anderson Steven David 
2/2/1980 Smith Adam [possibly null?]
3/3/1990 Taylor Ed [possibly null?]

How do I join the tables to introduce new columns in the result set if needed to hold several first names or last names for one person?

Answer 1

Does your application really need to handle unlimited first/last names per person? I don’t know your specific needs, but that seems like it may be a little extreme. Regardless…

Since you can’t really have a dynamic number of columns returned, you could do something like this:

SELECT birthdate, lastname, GROUP_CONCAT(firstname SEPARATOR '|') AS firstnames
FROM Persons, PersonsLastNames, PersonsFirstNames
WHERE Persons.id = PersonsLastNames.id
AND Persons.id = PersonsFirstNames.id
GROUP BY Persons.id

This would return one row per person that has a last name, with the (unlimited) first names separated by a pipe (|) symbol, GROUP_CONCAT function.

birthdate             lastname   firstnames
---                   ---        ---
1970-01-01 00:00:00   Anderson   Steven|David
1980-02-02 00:00:00   Smith      Adam
1990-03-03 00:00:00   Taylor     Ed