Guy Rouillier wrote:
Jim Fitzgerald wrote:
Hi -
I have two tables, one of them has names of people and an associated
integer ID. The other table is a list of the people (from the first
table) by their ID number that have signed up for a class. How would
I write a query that would list all the people from the first table
that do not have any entries in the second table? Basically, I want
a listing of all my people who have not signed up for the class.
select *
from people
where id not in
(
select id
from class_registration
)
Wouldn't a NOT EXISTS be faster? After all, the current record can be
disposed of as soon as there's any reference to it from class_registration.
For example:
select *
from people
where not exists (
select 1
from class_registration
where id = people.id
);
It may be faster to use * or a specific column name in the subquery
instead of the constant value 1. EXPLAIN ANALYZE will tell ;)
--
Alban Hertroys
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