Actualización de la izquierda Únete a mysql
UPDATE t1
LEFT JOIN
t2
ON t2.id = t1.id
SET t1.col1 = newvalue
WHERE t2.id IS NULL
Obedient Okapi
UPDATE t1
LEFT JOIN
t2
ON t2.id = t1.id
SET t1.col1 = newvalue
WHERE t2.id IS NULLUPDATE TableB
SET TableB.value = (
SELECT TableA.value
FROM TableA
WHERE TableA.name = TableB.name
);UPDATE tableB
INNER JOIN tableA ON tableB.name = tableA.name
SET tableB.value = IF(tableA.value > 0, tableA.value, tableB.value)
WHERE tableA.name = 'Joe'