Question

I’m working on joining 3 tables.

table1.
grp_id | email_id
   1   |  3 
   1   |  58

table2.
sam_msg_id | sam_subject
   3       |  Funnel

table3.
id | subject
58 | testing check


Desired Output:

id |grp_id|email_id|sam_subject|subject      |
184|1     |3       |funnel     |             |
185|1     |58      |           |testing check|

the query I tried:

SELECT table1.*, table2.sam_subject, table3.* 
FROM table1
INNER JOIN table2 
    ON table2.sam_msg_id = table1.email_id 
INNER JOIN table3 
    ON table3.id = table1.email_id 
WHERE table1.grp_id = '1' 

What I’m trying to do here is to get the list of subject and its id from table2 and table3 where the id is found at table1 under email_id.

When I tried doing it with one inner join only by checking only the data from table2 it was working.

I am not familiar in using inner joins thus I can’t really see what I’m doing wrong.

I am using MySQL.

Answer 1

Sounds like you need a LEFT JOIN

SELECT table1.*, table2.sam_subject, table3.* 
FROM table1
LEFT JOIN table2 
    ON table2.sam_msg_id = table1.email_id 
LEFT JOIN table3 
    ON table3.id = table1.email_id 
WHERE table1.grp_id = '1' 

Based on you edit, the following should give you the results you want:

SELECT t1.grp_id, 
  t1.email_id, 
  coalesce(t2.sam_subject, '') sam_subject, 
  coalesce(t3.subject, '') subject
FROM t1
left JOIN t2 
    ON t2.sam_msg_id = t1.email_id 
left JOIN t3 
    ON t1.email_id = t3.id
WHERE t1.grp_id = '1' 

See SQL Fiddle with Demo