>>Here is a sample:
>>
>>

>>declare @t table (id int identity, col1 Int, col2 Int)
>>
>>insert into @t (col1, col2) values (1, 3), (2, 5)
>>
>>select * from @t where not (col1 > 3 and col2 < 6)
>>
>>select * from @t T where not exists (select * from @t T1 where col1 > 3 and col2 < 6 and T.id = T1.id)
>>
>>select * from @t where col1 <=3 or col2 >=6

>>
>>Normally NOT (condition1 and condition2) translates into opposite condition1 OR opposite condition2
>
>Yes, after second verification, I see that the execution is the same.
>
>I always use the NOT in such approach as it is more easy to understand. When I have something like this:
>
>

>DECLARE @ModDate DateTime
>DECLARE @NoStatus Int
>DECLARE @ModDate2 DateTime
>DECLARE @NoStatus2 Int
>DECLARE @ModDate3 DateTime
>DECLARE @NoStatus3 Int
>
>SET @ModDate='2013-11-09 10:31:18'
>SET @NoStatus=5
>SET @ModDate2='2014-11-03 10:31:18'
>SET @NoStatus2=8
>SET @ModDate3='2014-11-03 10:31:18'
>SET @NoStatus3=7
>
>SELECT Client.Numero FROM Client (NOLOCK)
> WHERE NOT (Client.ModDate<@ModDate AND Client.NoStatus=@NoStatus) AND
>  NOT (Client.ModDate<@ModDate2 AND Client.NoStatus=@NoStatus2) AND
>  NOT (Client.ModDate<@ModDate3 AND Client.NoStatus=@NoStatus3)
>

>
>...it seems more easy to understand that the second one:
>
>

>DECLARE @ModDate DateTime
>DECLARE @NoStatus Int
>DECLARE @ModDate2 DateTime
>DECLARE @NoStatus2 Int
>DECLARE @ModDate3 DateTime
>DECLARE @NoStatus3 Int
>
>SET @ModDate='2013-11-09 10:31:18'
>SET @NoStatus=5
>SET @ModDate2='2014-11-03 10:31:18'
>SET @NoStatus2=8
>SET @ModDate3='2014-11-03 10:31:18'
>SET @NoStatus3=7
>
>SELECT Client.Numero FROM Client (NOLOCK)
> WHERE (Client.ModDate>=@ModDate OR Client.NoStatus<>@NoStatus) AND
>  (Client.ModDate>=@ModDate2 OR Client.NoStatus<>@NoStatus2) AND
>  (Client.ModDate>=@ModDate3 OR Client.NoStatus<>@NoStatus3)
>

This thing is still very hard to understand for me. I think the easiest here would be

and Client.ModDate >=@MinDateOf3Dates OR Client.NoStatus NOT IN (@Status1, @Status2, @Status3)