Updates not correct

[Tison]

If I run the following script twice,I get different results.
Anyone know why ?

update steve_rev
set a.business_type = b.business_type,
a.history_amount = b.amount
from steve_rev a,
steve_tmp b
where a.account_no in ('3000', '5000')
and a.company_mnemonic = b.company_mnemonic
and a.treaty_number = b.treaty_number
and a.move_plan_code = b.move_plan_code
and a.period_ending_dt = b.period_ending_dt
and a.account_description = b.account_description
and a.account_no = b.account_no
and convert(char(8), a.posted_date, 112) = convert(char(8), b.

 

[Tim1]

By you get different answers, do you mean that you get a different count of rows affected, or the values in the columns are different?