编写一个查询，根据监视器的数量(userID)为每个用户创建新列(monitorID)

Question

我对SQL很陌生。我正在尝试编写一个查询，它根据监视器的数量(userID)为每个用户创建新列(monitorID)。

我的意图是使用公共表表达式(CTE)来计数监视器的数量，然后使用子查询来创建基于监视器计数的新列。

查询

WITH monitors_count AS (
SELECT userID, count(monitorID) as monitors_count,
FROM monitors
GROUP BY userID
)
 
SELECT
    userID,
    (SELECT 
        CASE 
            WHEN monitors_count.monitors_count > 100 THEN "> 100"
            ELSE "<100"
    END;
    FROM monitors AS inside_monitors
    WHERE inside_monitors.userID = outside_monitors.userID
    )
 
FROM monitors AS outside_monitors

谢谢你的建议。

Answer 1

 WITH monitors_count AS (
    SELECT userID, count(monitorID) as monitors_count
    FROM monitors
    GROUP BY userID
    )
     
    SELECT
        monitors.UserID,
        CASE 
        WHEN monitors_count.monitors_count > 100 THEN "> 100"
        ELSE "<100" end as monitor_count
    FROM monitors inner join monitors_count
    On monitors.UserID= monitors_count.UserID
    Group By monitors.UserID