How do I make multiple self joins in mysql?

Question

I am working on a genealogy database. In simple terms a single table called ancestors , consists of records with the following structure:

 name_id | name | mother_id | father_id
---------+------+-----------+-----------
       1 | John |         2 |         3
       2 | Mary |         4 |         5
       3 | Dave |         6 |         7

The first query finds parent ids for John: eg John has parents with ids 2 and 3

Then two further queries find the parent names for the parent ids: Parent id 2 has the name Mary, and Parent id 3 has the name Dave

Three queries have been used to find that: John has parents called Mary and Dave.

Can this be done with a single query, and will there be any gain in performance?

Answer 1

SELECT me.name,
       mother.name,
       father.name
  FROM ancestors me
  JOIN ancestors mother
    ON me.mother_id = mother.name_id
  JOIN ancestors father
    ON me.father_id = father.name_id
 WHERE ancestors.id = 1
;

And yes, it's generally faster to run the above than to run three separate lookup queries.

Answer 2

Join as you usually would, but simply use the same table each time, giving each join a unique alias:

SELECT people.name_id, people.name, mothers.name_id, mothers.name, ...
FROM people
LEFT JOIN people AS mothers ON people.mother_id = mothers.name_id
LEFT JOIN people AS fathers ON people.father_id = fathers.name_id
etc...

Answer 3

Have a look at graph noSQL databases. They are the perfect fit for what you plan to do:

• http://en.wikipedia.org/wiki/FlockDB

• http://en.wikipedia.org/wiki/NoSQL#Graph