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

问题描述

我是 sql 新手。我正在尝试编写一个查询，该查询根据监视器数量 (monitorID) 为每个用户 (userID) 创建新列。

我的意图是使用公用表表达式 (CTE) 来计算监视器的数量，然后根据监视器计数创建新列的子查询。

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

感谢您的建议。

解决方法

 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