MySQL select rows that do not have matching column in other table

Question

I can\'t seem to figure this out so far. I am trying to join two tables and only select the rows in table A that do not have a matching column in table B. For example, lets

Answer 1

Try this SQL:

SELECT users.username
FROM  users
LEFT JOIN sent ON sent.username = users.username
WHERE sent.username IS NULL;

The better way in my opinion would be:

SELECT users.username
FROM  users
LEFT JOIN sent ON sent.id = users.id
WHERE sent.id IS NULL;

As both the id fields, would be indexed (primary key I would have thought) so this query would be better optimised than the first one I suggested.

However you may find my first suggestion better for you, it depends on what your requirements are for your application.

Answer 2

Typically, you would use NOT EXISTS for this type of query

SELECT p.Name
FROM   pooltest p
WHERE  NOT EXISTS (SELECT s.Name
                   FROM   senttest s
                   WHERE  s.Name = p.Name)

An alternative would be to use a LEFT OUTER JOIN and check for NULL

SELECT p.Name
FROM   pooltest p
       LEFT OUTER JOIN senttest s ON s.Name = p.Name
WHERE  s.Name IS NULL

Note that the implicit join syntax you are using is considered obsolete and should be replaced with an explicit join.

Answer 3

May be this one can help you ....

I had also the same problem but Solved using this this query

INSERT INTO tbl1 (id,name) SELECT id,name from tbl2 where (name) not in(select name from tbl1);

hope this one will solve your problem