SQL 10 lekcija

SELECT `id`, (SELECT `user` FROM `users` WHERE `id`=id) as `user` FROM `testtable`;

SELECT `id_a`, (SELECT `name_b` FROM `userb` WHERE `id_b`=id_a) as `name_b` FROM `usera` ; 

SELECT `id`, (SELECT `user` FROM `userb` WHERE `id`=id) as `user` FROM `usera` WHERE `id`='';

SELECT `id_a`, (SELECT `name_b` FROM `userb` WHERE `id_b`=id_a) as `name_b` FROM `usera` WHERE `id_a`='2'; 
Piemeram: post un komentāri (select un subselect)
SELECT `user` FROM `usersa` UNION SELECT `user` FROM `usersb`;
 
SELECT `name_a` FROM `usera` UNION SELECT `name_b` FROM `userb`;  
SELECT `name_a` FROM `usera` UNION ALL SELECT `name_b` FROM `userb`;  

SELECT `name_b` INTO `usera` FROM `userb`; (MySQL - neatbalsta)