UPDATE
`table1` AS `dest`,
(
SELECT
*
FROM
`table2`
WHERE
`id` = x
) AS `src`
SET
`dest`.`col1` = `src`.`col1`
WHERE
`dest`.`id` = x
;
UPDATE tableA a
INNER JOIN tableB b ON a.name_a = b.name_b
SET validation_check = if(start_dts > end_dts, 'VALID', '')
-- where clause can go here