Question

I have a table of edge like this:

-------------------------------
| id | arg1 | relation | arg2 |
-------------------------------
| 1  |   1  |     3    |   4  |
-------------------------------
| 2  |   2  |     6    |   5  |
-------------------------------

where arg1, relation and arg2 reference to the ids of objects in another object table:

--------------------
| id | object_name |
--------------------
| 1  |   book      |
--------------------
| 2  |   pen       |
--------------------
| 3  |   on        |
--------------------
| 4  |   table     |
--------------------
| 5  |   bag       |
--------------------
| 6  |   in        |
--------------------

What I want to do is that, considering performance issues (a very big table more than 50 million of entries) display the object_name for each edge entry rather than id such as:

---------------------------
| arg1 | relation | arg2  |
---------------------------
| book |    on    | table |
---------------------------
|  pen |    in    | bag   |
---------------------------

What is the best select query to do this? Also, I am open to suggestions for optimizing the query – adding more index on the tables etc…

EDIT: Based on the comments below:

1) @Craig Ringer: PostgreSQL version: 8.4.13 and only index is id for both tables.

2) @andrefsp: edge is almost x2 times bigger than object.

Answer 1

It won’t get cheaper than this:

SELECT o1.object_name, r1.object_name, o2.object_name
FROM   edge e
JOIN   object o1 ON o1.id = e.arg1
JOIN   object  r ON  r.id = e.relation
JOIN   object o2 ON o2.id = e.arg2;

And you don’t need more indexes. The one on object.id is the only one needed for this query.

But I seriously doubt that you want to retrieve 50 millions of rows at once, and in no particular order. You still didn’t give the full picture.