INSERT INTO different fields in different database table - php

Question

I'm quite confused with sql INSERT INTO. Do I need to put JOIN? or INNER JOIN when I'm going to put into different table?
$sqlinsert = "INSERT INTO forum_topic (topic_title, topic_message, thread_id)
VALUES
('$topic','$message','$thread_id')";
I know this code is works for only one table but not for two. However, what I want is $message into post_message in other table.
In forum_topic table, there is post_id, post_message, date, and topic_id.
But there is forum_post table where I want to put $message into post_message in forum_post.
So, in forum_post table, there is post_id, post_message, date, and topic_id.
So do I need to JOIN or INNER JOIN? I don't know which one I should code them.
PS : I know the question is quite hard for you to understand. How I wish i can put image but I don't have 10 reputations, so i decided to do like this.

Answer 1

You cannot insert into multiple tables with one query, but you can use transactions to make sure that the operation is atomic.
BEGIN;
Your queries here
COMMIT;
When you need to execute several interdepending queries, some of them might result in error. So to keep the database consistent you would like to execute them as all-or-none (You can read about ACID).
MySQL also supports transactions but only with some of its storage engines (e.g. InnoDB, but not MyISAM).
The pseudo-code of usage looks like this.
start transaction
try {
execute query 1
execute query 2
...
commit transaction
catch {
rollback transaction
}
If you are using PDO, look at these functions.
In case of mysql_query, you can use
mysql_query("START TRANSACTION");
mysql_query("COMMIT");
mysql_query("ROLLBACK");

Answer 2

You don't use joins. You use separate queries for each table.
insert into table1
(field1, field2, etc)
values
(value1, value2, etc);
insert into table2
(field1, field2, etc)
values
(value1, value2, etc);

Answer 3

To insert into multiple tables you must use multiple queries.
Example:
$sqlinsert1 = "INSERT INTO forum_topic1 (topic_title1, topic_message1, thread_id1)
VALUES
('$topic1','$message1','$thread_id1')";
$sqlinsert2 = "INSERT INTO forum_topic2 (topic_title2, topic_message2, thread_id2)
VALUES
('$topic2','$message2','$thread_id2')";
Join are used for Selecting queries.
Example for a Join:
$sqlselect = "SELECT * FROM forum_topic
Join table2 on thread_id = table2id
WHERE topic_title = $topic";