We have a huge table which has 12 million records. And when I run the following script, it took 50 hours. Is there anyone who can help? Thanks.

update TableA
set In=e.In, EA=e.ea, We=e.we
from TableA c, TableB e
where c.code=e.code

TableA 12,000,000 records.
TableB 750,000 records.
And have clustered index on each code field.