SQL 服务器中的查询表达式中的语法错误（缺少运算符）

Question

I have some SQL code, and when I run it, I get an error:

SELECT AVG (DISTINCT E.salary) AS avrage
FROM aircraft AS A, certified AS C, employees AS E
WHERE A.cruisingrange > 1000 
  AND A.aid = C.aid 
  AND C.eid = E.eid

Error:

How can I fix this error?

Answer 1

MS Access does not directly support DISTINCT syntax inside of an aggregate function. One workaround here would be to take the average of a subquery which finds the distinct salaries:

SELECT AVG(salary) AS avrage
FROM
(
    SELECT DISTINCT E.salary
    FROM (aircraft AS A
    INNER JOIN certified AS C ON A.aid = C.aid)
    INNER JOIN employees AS E ON C.eid = E.eid
    WHERE A.cruisingrange > 1000
) t;

Note that I have also converted your old school implicit join syntax to modern explicit join syntax. This is the preferred way of writing SQL these days.