mysql update from another table if fields are not equal

Question

what's wrong with this query?

update TA,TB
set TA.change = 1,TA.value = TB.value
where
TA.name  = TB.name and TA.value <> TB.value

I want to update TA from TB when value change in TB

Answer 1

Your query is okay. I would write it with an explicit join :

update TA join
       TB
       on TA.name  = TB.name
     set TA.change = 1,
         TA.value = TB.value
where TA.value <> TB.value;

You might need to take NULL values into account:

update TA join
       TB
       on TA.name  = TB.name
     set TA.change = 1,
         TA.value = TB.value
where not (TA.value <=> TB.value);