Question

我有三张桌子

tbl_worker

City   WorkerName     Job
 10     Raymond    Carpenter
 10     Sara       Programmer 
 11     John       Painter
 11     Alice      Booker

tbl_workshop

City    WorkshopName   
 10       Dell         
 11       Apple
 10       Sony 

Tbl_city
  Id    Name
  10    Mexico
  11    Sydney

现在我想要这样的结果：

City    WorkersQty    WorkshopQry
 Mexico     2               2
 Sydney     2               1

结果返回在不同城市注册的工人和工作坊的数量。我应该写什么查询？

Answer 1

分别对tbl_workshop和tbl_worker表进行分组，然后使用LEFT JOIN获取结果：

SELECT c.City,
    k.Cnt AS WorkersQty,
    w.Cnt AS WorkshopQry
FROM Tbl_city c
  LEFT JOIN (
    SELECT City, COUNT(*) Cnt
    FROM tbl_worker
    GROUP BY City
    ) k ON c.ID = k.City
  LEFT JOIN (
    SELECT City, COUNT(*) Cnt
    FROM tbl_workshop
    GROUP BY City
    ) w ON c.ID = w.City

如果您只想显示有工作室或工作人员的城市，请添加：

WHERE k.Cnt > 0 OR w.Cnt > 0

Answer 2

使用Dense_rank获取研讨会或工作人员的数量

SELECT city, MAX(WorkshopQty) AS WorkshopQty , MAX(WorkersQty) AS WorkersQty
FROM (
        SELECT c.name AS City, 
               DENSE_RANK() OVER (PARTITION BY c.id ORDER BY WorkshopName) AS WorkshopQty,
               DENSE_RANK() OVER (PARTITION BY c.id ORDER BY WorkerName) AS WorkersQty  
        FROM tbl_city c
        INNER JOIN tbl_workshop s ON s.city = c.id
        INNER JOIN tbl_worker w ON w.city = c.id
    ) s
GROUP BY City

按照三个表格分组

2 个答案: