MySQL从表中获取数据，并检查表行中是否存在userid

Question

I have a table called " session ", the table has a column called " userid ".

Example of the table:

ROW    userid
-------------
1      61
2      128
3      84

Now in my site I have articles listed all on ONE page, EACH article is written by a user, and EACH user has it's own userid

What I'm trying to achieve is: IF the user(userid=X) which wrote the article EXISTS in session table show a text..

Here is how I'm trying to get the userid from the session table ->

SELECT userid FROM #session

But I guess with this code it only takes ONE userid from the column not ALL of them...

Can someone give me a hand on this please? Thank you

Answer 1

Hope you have also database table for articles (table article with column userid) , you may use inner join in your query:

Select userid FROM article 
JOIN session using(userid)

This will get all users that are in session table and have the article

Answer 2

The following will select ALL userid's from session:

SELECT userid FROM session

...which is almost exactly the code you mentioned. However, you don't need to get a list of userid's, you just need to see if a certain id exists in the table. So, what you do is you count the number of instances that the userid is a specific value, which would look something like this (in php, using mysqli):

function is_id_in_session($db, $userid) {
    $total_result = $db->query("SELECT COUNT(userid) FROM session WHERE userid = {$userid}");
    $total = $total_result->fetch_row();
    return ($total[0] > 0);
}