First, this isn't really the right place to ask -- this forum is about performance, not SQL syntax.
Second, this isn't a question anyone can answer in a reasonable length of time. What you're asking for usually is taught in a class on relational database theory, which is typically a semester or two in college.
If you really need a crash course, dig around on the web for terms like "SQL Tutorial".
Good luck,
Craig
J@xxxxxxxxxxx wrote:
Hey guys, how u been. This is quite a newbie question, but I need to ask
it. I'm trying to wrap my mind around the syntax of join and why and
when to use it. I understand the concept of making a query go faster by
creating indexes, but it seems that when I want data from multiple
tables that link together the query goes slow. The slow is typically due
to expensive nested loops. The reason is, all my brain understands is:
select
tablea.data
tableb.data
tablec.data
from
tablea
tableb
tablec
where
tablea.pri_key = tableb.foreign_key AND
tableb.pri_key = tablec.foreign_key AND...
From what I read, it seems you can use inner/outer right/left join on
(bla) but when I see syntax examples I see that sometimes tables are
omitted from the 'from' section of the query and other times, no.
Sometimes I see that the join commands are nested and others, no and
sometimes I see joins syntax that only applies to one table. From what I
understand join can be used to tell the database the fast way to murge
table data together to get results by specifiying the table that has the
primary keys and the table that has the foreign keys.
I've read all through the postgres docs on this command and I'm still
left lost. Can someone please explain to me in simple language how to
use these commands or provide me with a link. I need it to live right
now. Thanx.
