How to echo the post's content - php

Question

I have two tables like this:
posts table:
post_id subject
1 abc
2 def
and contents table, of which the post_id column is the foreign key:
content_id post_id content date
1 1 main content 2014-07-31 03:02:00
2 1 reply one 2014-07-31 03:03:20
3 1 reply two 2014-07-31 03:06:32
As you can see, the contents table stores both the post's content and its possible repli(es). Here, in this example, the post_id # 1 has its main content and two replies.
What I want to do is to echo the subject and its content only, but not the replies. So I have coded the query like this:
$query = "SELECT subject, content
FROM posts As p
INNER JOIN contents AS c USING (post_id)
ORDER BY post_id DESC";
$result = mysqli_query ($dbc, $query)
while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
echo "{$row['content']}n\";
}
Then you know what?. It echoes out the latest content of the post, which is the content_id # 3. However, what I wanted to do is to echo the post's content, which is the oldest content_id of the post_id # 1.
Can you help me, please?

Answer 1

UPDATED
It basically selects the minimum date per post in a subquery and uses it as a key for the "normal" query to look for.
SELECT distinct subject, content FROM content c
JOIN post p
on c.post_id = p.post_id
WHERE cast(c.post_id as char)+cast(c.contentdate as char)in
(
SELECT
cast(p.post_id as char)+cast(min(c.contentdate) as char) as KeyValue
FROM post p
INNER JOIN content c on p.post_id = c.post_id
GROUP BY p.post_id
)
This returns me:
subject | content
----------------------
asd | main content
def | main content

Answer 2

MIN(DATE) has to be content, so you need to GROUP the id with the DATE
Join both tables on the basis of post_id and then group on the basis of min(date)
$query = "SELECT p.post_id, p.subject, c.content, c.date
FROM posts p
INNER JOIN contents c on p.post_id = c.post_id
WHERE date = (select min(date)
from contents ct
where ct.post_id = p.post_id
)
GROUP BY post_id,subject,content, date
ORDER BY post_id DESC";
$result = mysqli_query ($dbc, $query)
while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) {
echo "{$row['content']}n\";
}

Answer 3

Try this
$query = "SELECT subject, content
FROM posts As p
INNER JOIN contents AS c USING (post_id)
ORDER BY date ASC, post_id DESC";

Answer 4

You need to order results by content_id (or date) too. So the sql query might look like this:
$query = "SELECT subject, content
FROM posts As p
INNER JOIN contents AS c USING (post_id)
ORDER BY post_id DESC, content_id ASC";
And, of course, I assume that the main content has added to database before the replies and you will not alter the row indexes which might lead to situation where the first row with certain post_id isn't the actual content.
So, if you want to print out everything you need to do something in your code. You need to print only the first ones of rows with same post_id:
$last_post_id = 0;
while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
if ($last_post_id != $row['post_id']) {
echo "{$row['content']}n\";
}
$last_post_id = $row['post_id'];
}

Answer 5

After testing all the answers here, I chose the answer of #NoobEditor. However, I have to make it clearer as follows:
$query = "SELECT p.post_id, p.subject, c.content, c.date
FROM posts p
INNER JOIN contents c on p.post_id = c.post_id
WHERE date = (select min(date)
from contents c
where c.post_id = p.post_id
)
GROUP BY c.post_id
ORDER BY p.post_id DESC";
$result = mysqli_query ($dbc, $query)
In which I made it clearer at the GROUP and ORDER BY functions. And use c as alias for contents table, but not need to use c and ct
while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) {
echo "{$row['content']}n\";
}