Question

I have 2 tables : Users and Documents.

1 User can have 0 or several documents.

I would like to display each user and their documents, but the problem : I would like to display users that have no documents, in a result like this (assume IdUsers 3 and 5 have no documents):

IdUser IdDocument DocumentName
====== ========== ============
1      1          test11.pdf
1      2          test12.pdf
1      3          test13.pdf
2      4          test21.pdf
2      5          test21.pdf
3      NULL       NULL
4      6          test41.pdf
5      NULL       NULL

Answer 1

You will use a LEFT JOIN to perform this operation.

create table users
(
  userid int
)

create table documents
(
  documentid int,
  userid int,
  documentname varchar(10)
)

insert into users values (1)
insert into users values (2)
insert into users values (3)
insert into users values (4)

insert into documents values (1, 1, 'test')
insert into documents values (2, 1, 'test 1')
insert into documents values (3, 2, 'test 2')
insert into documents values (3, 3, 'test 3')

select *
from users u
left join documents d
on u.userid = d.userid

see a sqlfiddle for a test

You should do some research on JOINs, here is a good description of the JOINs:

A Visual Explanation of SQL Joins