查询以获取总行数和不同行之间的差异

Question

我是SQL的新手，无法编写正确的SQL。给定一个表STATION，其中包含五个字段的数据，即ID，CITY，STATE，NORTHERN LATITUDE和WESTERN LONGITUDE。

+-------------+------------+
| Field       |   Type     |
+-------------+------------+
| ID          | INTEGER    |
| CITY        | VARCHAR(21)|
| STATE       | VARCHAR(2) |
| LAT_N       | NUMERIC    |
| LONG_W      | NUMERIC    |
+-------------+------------+

让NUM成为城市的数量，NUMunique是独特城市的数量，然后写一个查询来打印NUM - NUMunique的值。

我试过了：

select (count(CITY)- distinct count(CITY)) from STATION; 

Answer 1

您可以在计数内使用select distinct并尝试这种方式

select  (count(CITY)- count(distinct CITY)) from STATION; 

Answer 2

select (count(CITY)- count(distinct CITY)) from STATION;

脚注：您可以查看以下sql函数计算数学值：count，avg，sum，+， - ，*，％

Answer 3

SELECT COUNT(CITY) - COUNT(DISTINCT CITY) AS N FROM STATION;

查询结果别名为N。

Answer 4

SELECT (COUNT(CITY)- COUNT(DISTINCT(CITY))) AS diff
FROM STATION