Question

I am having below tables.

create table test(int id,int data1);
create table test1(int id,int data2);

insert into test values(1,1,);
insert into test1 values(2,2);
insert into test1 values(3,3);

insert into test1 values(1,1);

Now I want the rows of test, that don’t participate in join. i.e I want rows (2,2) and (3,3). I want to be able to do this in mysql.

I don’t want to use inner query because of performance.

Thank you

Answer 1

Using LEFT JOIN/IS NULL:

   SELECT t1.*
     FROM TEST1 t1
LEFT JOIN TEST t ON t.id = t1.id
                AND t.data1 = t1.data2
    WHERE t.id IS NULL

Assuming the columns being joined on, this is the fastest/most efficient method on MySQL. Otherwise, NOT IN/NOT EXISTS are better choices.

Using NOT EXISTS:

SELECT t1.*
  FROM TEST1 t1
 WHERE NOT EXISTS(SELECT NULL
                    FROM TEST t
                   WHERE t.id = t1.id
                     AND t.data1 = t1.data2)