Question

I have a scenario like this, there are 2 tables table_1 and table_2. Both table have a common column called column_1(no foreign_Key constraints!!). Table_1 can have some extra rows which are not present in table_2(In other words, table_2 is a sub-set of table_1). I want to list all those items which are only present in table_1 but not in table_2.
Kindly help in writing the sql query for the same.
Thanks in advance.

Answer 1

SELECT a.*
FROM   table1 a
       LEFT JOIN table2 b
           on a.column_1 = b.column_1
WHERE b.column_1 IS NULL

if those two tables are not related with each other, better add an index on table1.column_1 and table2.column_1 so that it won’t require full table scan (which slows the performance)