Selecting from multiple tables.

[Halide]

Ok, I'm not very experienced with SQL yet, everything I do know is self-taught. Anywho, where's a good place to learn about selecting from multiple tables.

And can you "link" fields like in MS Access?

[sans-hubris]

What exactly are you trying to do? Might you not wish to do a JOIN?

[_underdog]

www.w3schools.com has a good SQL tutorial.

[Halide]

not sure about JOIN? :) I'll check out the tutorial, thanks

[Halide]

hmm i took the quiz and i got 100% but the questions were way too easy

[Halide]

these join's are kind of confusing...
i'm not sure if i can do what i want with it?

I have a table names forum_topics and forum_replies

forum_replies has a field specifying the topic id, id from forum_topics is the same

so can i select posts from both tables using an INNER JOIN?

[iDxMan]

What have you tried so far?


SELECT *
FROM table1 as a, table2 as b
WHERE a.topic_id = 'var_goes_here'
AND a.topic_id = b.topic_id

[Halide]

I haven't tried anything yet, cause I'm not sure I want to mess up my code... although it would be better that way?

do you not need any join code in the statement?

[Grizzly]

The "join code" is taking place on the line which says:


AND a.topic_id = b.topic_id


That statement establishes a relationship between table (a) and table (b). This is the true-blue, standard way of joining tables.

The "JOIN" statement you're looking for is more or less a Microsoft invention, and therefore it generally only works on MS databases (MSSQL, Access) I think a few other DBMS vendors have adopted it though.

[Halide]

ok does this look reasonable:

SELECT title, text
FROM forum_topics, forum_replies
WHERE forum_topics.id = <TOPICID>
AND forum_topics.id = forum_replies.topic_id

I have no idea what the "AS blah" is needed for?

[gufmn]

Originally posted by Halide


I have no idea what the "AS blah" is needed for? [/B]

It's so you don't have to keep typing table1 or table2. By using AS, you can just call them by whatever you aliased them AS.

For instance:

a.topic_id


instead of:

table1.topic_id

Not really needed if you're writing minimal statements or if the table names are short and easy to remember. But, I'm sure you can see how it could be usefull.

[Halide]

ok I'll try it :)

[iDxMan]

Originally posted by gufmn

Not really needed if you're writing minimal statements or if the table names are short and easy to remember. But, I'm sure you can see how it could be usefull.

For us lazy folk. :) Actually I do it all the time, but its really handy when you have long table names.