timestamp         | machine_status | product_code
----------------------|----------------|---------------
'2017-03-01 00:49:02' |       NULL     |      1
'2017-03-01 00:49:06' |       NULL     |     NULL
'2017-03-01 00:49:10' |        2       |      3
'2017-03-01 00:49:14' |       NULL     |     NULL
'2017-03-01 00:49:18' |        5       |     NULL
'2017-03-01 00:49:22' |       NULL     |     NULL
'2017-03-01 00:49:26' |        3       |      0
'2017-03-01 00:49:30' |       NULL     |     NULL
'2017-03-01 00:49:34' |       NULL     |      6

timestamp         | machine_status | product_code
----------------------|----------------|---------------
'2017-03-01 00:49:02' |       NULL     |      1
'2017-03-01 00:49:06' |       NULL     |      1
'2017-03-01 00:49:10' |        2       |      3
'2017-03-01 00:49:14' |        2       |      3
'2017-03-01 00:49:18' |        5       |      3
'2017-03-01 00:49:22' |        5       |      3
'2017-03-01 00:49:26' |        3       |      0
'2017-03-01 00:49:30' |        3       |      0
'2017-03-01 00:49:34' |        3       |      6

update `recent_grouped`
set     `machine_status` = (@n := COALESCE(`machine_status`, @n))
order by `timestamp`;