Re: Data Warehouse Reevaluation - MySQL vs Postgres -- merge tables

Performance hint :

For static data, do not normalize too much.
For instance if you have a row which can be linked to several other rows,
you can do this :

create table parents (
id serial primary key,
values... )

create table children (
id serial primary key,
parent_id references parents(id),
integer slave_value )

Or you can do this, using an array :

create table everything (
id serial primary key,
integer[] children_values,
values... )

Pros :
No Joins. Getting the list of chilndren_values from table everything is
just a select.
On an application with several million rows, a query lasting 150 ms with
a Join takes 30 ms with an array.
You can build the arrays from normalized tables by using an aggregate
function.
You can index the array elements with a GIST index...

Cons :
No joins, thus your queries are a little bit limited ; problems if the
array is too long ;