DELETE `ud`.*
FROM `userdata` AS `ud`
JOIN (
SELECT CONCAT('ufi', `uf`.`dbIncrement`) AS `dataId`
FROM `ufields`
WHERE `podvedId` = 'val'
AND `formId` = 'val'
AND `parentContainerId` = 'val'
AND (`descriptor_y` = 'val' OR `descriptor_y` = 'val')
) AS `uf` ON `uf`.`dataId` = `ud`.`dataId`
fabs(round(dotNum)-dotNum) > eps