使用同一表子查询结果的SQL更新

Question

I have a table of data like this:

-------------+-------------+-------
| foo_date   | description | flag |
-------------+-------------+-------
| 2014-01-01 | asdf 123    | 1    |
-------------+-------------+-------
| 2014-01-01 | FOO         | 1    |
-------------+-------------+-------
| 2014-01-02 | asdf 456    | 1    |
-------------+-------------+-------

I'm trying to set the flag to 0 for any rows where description isn't "FOO" and there is a row on the same date that is "FOO". So, in this example data set the first row would get flag = 0 because there is a FOO for the same date, but the third row wouldn't because there is no matching FOO for that date. Here's what I've come up with that works but it doesn't feel like the most efficient way of doing it.

UPDATE
  foo_table t1
JOIN
(
  SELECT 
    * 
  FROM 
    foo_table
  WHERE
    (foo_date) IN 
    (
      SELECT 
        foo_date
      FROM 
        foo_table 
      WHERE 
        description LIKE 'FOO%'
    )
    AND description NOT LIKE 'FOO%'
) AS t2
ON
(
  t1.foo_date = t2.foo_date
  AND t1.description = t2.description
)
SET
  t1.flag = 0

Answer 1

update t1
set t1.flag = 0
from foo_table t1
where     t1.description <> 'FOO'
      and exists (select * 
                  from foo_table t2 
                  where     t2.foo_date=t1.foo_date 
                        and t2.description = 'FOO')

Answer 2

Depending on your data, this may be more efficient:

update t1
set t1.flag = 0
from foo_table t1
where isnull(t1.description,'') <> 'FOO'
and t1.foo_date in (select t2.foo_date 
                  from foo_table t2 
                  where t2.description = 'FOO')