Question

我的查询如下：

linear-gradient(to left, currentcolor, currentcolor);

但是，我的查询无法很好地执行，我收到此错误：

Msg 102，Level 15，State 1，Server WIN-ILO9GLLB9J0，Line 33
＆＃39;）＆＃39;
附近的语法不正确

请帮我解决这个问题。

Answer 1

在SQL Server或MySQL中需要子查询的别名：

SELECT COUNT(*)
FROM (SELECT h2.hacker_id, count(c2.challenge_id) as co
      FROM hackers h2 INNER JOIN 
           challenges c2
           ON h2.hacker_id = c2.hacker_id
      GROUP BY h2.hacker_id
      HAVING count(c2.challenge_id) = 1
     ) x;

假设您的hacker_id都已明确定义，则不需要JOIN：

SELECT COUNT(*)
FROM (SELECT c2.hacker_id, count(c2.challenge_id) as co
      FROM challenges c2
      GROUP BY c2.hacker_id
      HAVING count(c2.challenge_id) = 1
     ) x;

如果您在challenges中有唯一ID，则还可以将其标记为：

select count(*)
from challenges c
where not exists (select 1
                  from challenges c2
                  where c2.hacker_id = c.hacker_id and c2.challenge_id <> c.challenge_id
                 );

使用challenges(hacker_id, challenge_id)上的索引，这应该具有最佳性能（再次，无论数据库如何）。

Answer 2

您需要FROM（）表的表名，例如在结束后添加一个简单的T）

SELECT COUNT(*)
FROM (
    SELECT h2.hacker_id, count(c2.challenge_id) as co
    FROM hackers h2 INNER JOIN challenges c2 ON h2.hacker_id = c2.hacker_id
    GROUP BY h2.hacker_id
    HAVING count(c2.challenge_id) = 1
) T

查询计数的SQL Server计数值

2 个答案: