Código SQL:
Ver originalINSERT INTO clientes2
SELECT t1.id FROM clientes AS t1
LEFT JOIN clientes2 AS t2 ON (t1.id=t2.id)
WHERE t2.clientes IS NULL
INSERT INTO clientes2
SELECT t2.id FROM clientes AS t1
LEFT JOIN clientes2 AS t2 ON (t1.id=t2.id)
WHERE t2.clientes IS NOT NULL