mssql not in not exists

There are three ways to do such a query:

• LEFT JOIN / IS NULL:

  SELECT  *
  FROM    common
  LEFT JOIN
          table1 t1
  ON      t1.common_id = common.common_id
  WHERE   t1.common_id IS NULL

• NOT EXISTS:

  SELECT  *
  FROM    common
  WHERE   NOT EXISTS
          (
          SELECT  NULL
          FROM    table1 t1
          WHERE   t1.common_id = common.common_id
          )

• NOT IN:

  SELECT  *
  FROM    common
  WHERE   common_id NOT IN
          (
          SELECT  common_id
          FROM    table1 t1
          )

When table1.common_id is not nullable, all these queries are semantically the same.

When it is nullable, NOT IN is different, since IN (and, therefore, NOT IN) return NULL when a value does not match anything in a list containing a NULL.

This may be confusing but may become more obvious if we recall the alternate syntax for this:

common_id = ANY
(
SELECT  common_id
FROM    table1 t1
)

The result of this condition is a boolean product of all comparisons within the list. Of course, a single NULL value yields the NULL result which renders the whole result NULL too.

We never cannot say definitely that common_id is not equal to anything from this list, since at least one of the values is NULL.

출처 : http://stackoverflow.com/questions/1406215/sql-select-where-not-in-subquery-returns-no-results