SQL

mysql update field from one table to another

UPDATE MY_TABLE AS t1
INNER JOIN MY_OTHER_TABLE AS t2 ON t1.COLID = t2.COLID
SET t1.COL1 = t2.COL1, t1.COL2 = t2.COL2
WHERE t1.COL3 = 'OK';

mysql update table from select on another table

UPDATE TableB 
SET TableB.value = (
    SELECT TableA.value 
    FROM TableA
    WHERE TableA.name = TableB.name
);

mysql update table from another table

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'

mysql update column with value from another table

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'