在mysql中内部联接多个表

Question

I Have three tables in my database users , posts and comments.

Their Structure is as follow :

**users** : 
user_id , user_name
**posts**: 
post_id , post_content, user_id
**comments** :
comment_id , comment_content , post_id, user_id

now i want to fetch data from these three tables using join in a following way : comment_id, comment_content, user_id, user_name, post_id can anyone plz tell me that how this can be done ? I Shall be very thankful.

Answer 1

It's a simple JOIN .

Try this:

select c.comment_id,
    c.comment_content,
    u.user_id,
    u.user_name,
    c.post_id
from comments c
join users u on u.user_id = c.user_id;

If you need columns from posts table too, join it:

select c.comment_id,
    c.comment_content,
    u.user_id,
    u.user_name,
    p.post_id,
    p.post_content
from comments c
join users u on u.user_id = c.user_id
join posts p on c.post_id = p.post_id;