[SQL] How does this query work.....?

[RbrtBrn3]

Hi,

I am using the following query to find the attributes of a given table, and 
their datatypes:

select typname,attname   
from pg_class c, pg_attribute a,pg_type t
where relname = 'table_name' and
attrelid = c.oid and
atttypid = t.oid and
attnum > 0;

Can anybody explain how this query actually works - I cannot figure it. 
Thanks in advance.

Rob Burne.

[SQL] Can anyone explain how this works?

[RbrtBrn3]

Hi,

I recently posted this same question a few weeks back but lost the reply 
someone kindly sent. The question again how exactly does this query work:

it will return all attributes and respective data types of a given table':

select attname, typname
from pg_class c, pg_attribute a, pg_type t
where relname = relation_name and
attrelid = c.oid and
atttypid = t.oid and
attnum > 0
order by attnum;

Many thanks,

Rob Burne.