Question

I have two tables in a firebird 1.5 database, the tables are client and notes, in the notes table there can be multiple records for each corresponding record in Client table, and sometimes none.
The tables are structured like

Client

Client_id   name
----------------- 
1           Sam 
2           Lee
3           Steve 
4           Linda 
5           Sue 
6           Jill 
7           Jack 

Notes

Notes_id   client_id   Note 
------------------------------ 
1          1           New
2          1           do not send
3          2           old
4          2           likes
5          4           do not send
6          5           new
7          5           Cats and Dogs
8          5           drives

I would like to run a select statement that would only return records from the Client table where there is no note named ‘do not send’ linked to the client in the notes table. So with the above examples the select statement would only return the following records from the client table.

Client_id   name
----------------- 
2           Lee
3           Steve 
5           Sue 
6           Jill 
7           Jack 

Is this possible? Any assistance with this would be appreciated.

Regards Alan

Answer 1

Below are three queries that will do the task:

SELECT
  c.*
FROM
  client c 
WHERE
  NOT EXISTS(SELECT * FROM notes n WHERE n.client_id = c.client_id 
    AND n.note = 'do not send')

or

SELECT
  c.*, n.client_id
FROM
  client.c LEFT JOIN
    (SELECT client_id FROM notes WHERE note = 'do not send') n
  ON c.client_id = n.client_id
WHERE
  n.client_id IS NULL

or

SELECT
  c.*
FROM
  client c 
WHERE
  NOT c.client_id IN (SELECT client_id FROM notes n 
    WHERE n.note = 'do not send')