mysql update table from another table
snippet in sql

update left join mysql

user8229

UPDATE  t1
LEFT JOIN
        t2
ON      t2.id = t1.id
SET     t1.col1 = newvalue
WHERE   t2.id IS NULL

mysql UPDate with enner join

user8936

UPDATE T1, T2,
[INNER JOIN | LEFT JOIN] T1 ON T1.C1 = T2. C1
SET T1.C2 = T2.C2, 
    T2.C3 = expr
WHERE condition

mysql update table from another table

user2712

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'