假设您的表名为T，字段名为F：

SELECT COUNT(F)
FROM (
    SELECT F
    FROM T
    GROUP BY F
    HAVING COUNT(*) = 1
) AS ONLY_ONCE

select count(*) from 
(
  select
    col1, count(*)
  from 
    Table
  group by 
    Col1
  Having 
    Count(Col1) = 1
)

把它放进窝里。

select count( cnt ) from
( select count(mycol) cnt from mytab group by mycol )
where cnt = 1

select field1, count(field1) from my_table group by field1 having count(field1) = 1

select count(*) from (select field1, count(field1) from my_table group by field1 having count(field1) = 1)

第一个函数将返回唯一的元素，第二个函数将返回唯一元素的数量。

难道就这么简单：

Select count(*) From MyTable Group By MyColumn Where Count(MyColumn) = 1

这就是我所做的，它的工作：

SELECT name 
FROM people JOIN stars ON stars.person_id = people.id 
JOIN movies ON movies.id = stars.movie_id
WHERE year = 2004
GROUP BY name, person_id ORDER BY birth;

注意：我在这里使用了几个表。
CS50问题集7（pset 7）9.sql修复！！