Write an SQL query: there is a clients table and a blacklist table with an id field. You need to select all clients who are not in the blacklist. Offer several solutions.

To select clients who are not in the blacklist, you can use several SQL query options:

1. Using LEFT JOIN with NULL check:

SELECT c.*
FROM clients c
LEFT JOIN blacklist b ON c.id = b.id
WHERE b.id IS NULL;

2. Using NOT IN:

SELECT *
FROM clients
WHERE id NOT IN (SELECT id FROM blacklist);

3. Using NOT EXISTS:

SELECT *
FROM clients c
WHERE NOT EXISTS (
  SELECT 1 FROM blacklist b WHERE b.id = c.id
);

Each of these options has its own performance characteristics depending on the DBMS and data volume.