>>The select is the same as you're currently using. I just want to see how long will it take. Your actual select should use SUM and GROUP BY Client.ClientNo, but let's first find out without SUM.
>
>I still do not understand. There is no direct relation with a record in my Client table.
>
>IAC, here is the result:
>
>Primary key SecondValue
>4168140 14400
>4168140 14400
>4168140 10800

To the select statement also add the BT dates.

That select statement is exactly what you have written in your update. You wanted to update client table and you wanted to connect both tables based on date ranges.