>I would rewrite it into a form like
>
>

>UPDATE Client
>	SET DayBetweenFirstAcceptSoldDate = CASE WHEN ....WHEN ... WHEN ... THEN ... ELSE 0 END
>	FROM Client
>		LEFT JOIN BusinessTime ON ....
>		LEFT JOIN Company ON ....
>		LEFT JOIN Research ON ....
>

>
>This will give the optimizer a chance to get you the best performance possible.

Yes, I had that at first but this creates a too long command as I need to repeat pretty much the entire base command. By putting the CASE WHEN inside the WHERE clause, this allows to keep the core of the command as is but only to add an exception down below.