SQL语法错误（缺少运算符）

Question

我有这个问题：

SELECT COUNT (DISTINCT Class)
    from student ;

我得到了：

  

此查询中的语法错误（缺少运算符）。

Answer 1

你可能在此之后：

SELECT COUNT(*) As ClassCount
FROM (SELECT DISTINCT Class FROM student);

或：

SELECT COUNT(*) As ClassCount
FROM (SELECT DISTINCT Class FROM student) AS T;