I have a weird situation. I have a select like this:

DECLARE @Active Bit
DECLARE @PayAccept Bit
DECLARE @AddDate DateTime
DECLARE @Loss_Code Varchar(1)
DECLARE @NoDetailType Integer
DECLARE @NoDetailType2 Integer
DECLARE @NoDetailType3 Integer
DECLARE @NoDetailType4 Integer
DECLARE @NoDetailType5 Integer

SET @Active=1
SET @PayAccept=0
SET @AddDate='2009-12-09 15:59:51'
SET @Loss_Code=' '
SET @NoDetailType=5
SET @NoDetailType2=6
SET @NoDetailType3=10
SET @NoDetailType4=12
SET @NoDetailType5=8

 SELECT M2.AI
 FROM M AS M2
 INNER JOIN B ON M2.NoBilling=B.Numero
 INNER JOIN (
   SELECT E.NoEntity,E.NoProvince
   FROM E
   WHERE E.Active=@Active AND E.PayAccept=@PayAccept
  ) EResult ON EResult.NoEntity=M2.NoEntity
 WHERE M2.AddDate<@AddDate AND
  B.NoProvince=EResult.NoProvince AND
  M2.Loss_Code=@Loss_Code AND
 (M2.NoDetailType=@NoDetailType OR M2.NoDetailType=@NoDetailType2 OR
  M2.NoDetailType=@NoDetailType3 OR M2.NoDetailType=@NoDetailType4 OR
  M2.NoDetailType=@NoDetailType5)

The table names have been adjusted to only keep the first letter to preserve the confidentiality of table names.

This select returns 27456 records.

Now, the goal to do this select is to update a field in the master table for those that are part of the result, in this case, 27456 records. So, what I did was the encapsulate that command into an update command such as this:

DECLARE @Active Bit
DECLARE @PayAccept Bit
DECLARE @AddDate DateTime
DECLARE @Loss_Code Varchar(1)
DECLARE @NoDetailType Integer
DECLARE @NoDetailType2 Integer
DECLARE @NoDetailType3 Integer
DECLARE @NoDetailType4 Integer
DECLARE @NoDetailType5 Integer

SET @Active=1
SET @PayAccept=0
SET @AddDate='2009-12-09 15:59:51'
SET @Loss_Code=' '
SET @NoDetailType=5
SET @NoDetailType2=6
SET @NoDetailType3=10
SET @NoDetailType4=12
SET @NoDetailType5=8

UPDATE M
 SET Loss_Code='1'
 FROM M
 INNER JOIN (
 SELECT M2.AI
 FROM M AS M2
 INNER JOIN B ON M2.NoBilling=B.Numero
 INNER JOIN (
   SELECT E.NoEntity,E.NoProvince
   FROM E
   WHERE E.Active=@Active AND E.PayAccept=@PayAccept
  ) EResult ON EResult.NoEntity=M2.NoEntity
 WHERE M2.AddDate<@AddDate AND
  B.NoProvince=EResult.NoProvince AND
  M2.Loss_Code=@Loss_Code AND
 (M2.NoDetailType=@NoDetailType OR M2.NoDetailType=@NoDetailType2 OR
  M2.NoDetailType=@NoDetailType3 OR M2.NoDetailType=@NoDetailType4 OR
  M2.NoDetailType=@NoDetailType5)
 ) MResult ON MResult.AI=M.AI

So, basically, the update part contains a relationship into its own table by the use of the AI field. As surprisinly as it gets, it only updates 26401 records. So, there is something I am missing here. I just don't understand why the update doesn't update all of the 27456 records.