使用LEFT JOIN进行MySQL查询，并具有来自另一个表的OrderID的计数…卡住了

Question

This is my current query and it's working fine as I expect it.

SELECT a.ID, a.CreatedDate, a.Status, b.OrderTotal, 
    e.Rate, f.RouteType, f.Code, g.Country, h.Network 
    from orders AS a
     LEFT JOIN order_details AS b ON a.ID = b.OrderID
     LEFT JOIN order_routes AS d ON a.ID = d.OrderID
     LEFT JOIN userrate AS e ON e.ID = d.RouteID
     LEFT JOIN ratelist AS f ON f.ID = e.RateListID
     LEFT JOIN country AS g ON f.CountryID = g.ID
     LEFT JOIN network AS h ON f.NetworkID = h.ID
     WHERE a.UserID = 16 ORDER BY a.CreatedDate DESC

However now I am trying to add another column which shows me count of appearances of each OrderID from order_routes

My order routes look like this right now

ID   OrderID   RouterID
1      1         1
2      1         2
3      2         2
4      2         3
5      2         5

So I want column which shows me how many appearances OrderID have in order_routes table.

I think I need sub query inside my query but when I try that it giving me error. To let you know

a.ID = d.OrderID

e.ID = d.RouteID

Please help.

Answer 1

try this

SELECT a.ID, a.CreatedDate, a.Status, b.OrderTotal, 
    e.Rate, f.RouteType, f.Code, g.Country, h.Network, d2.cnt AS OrderCount 
FROM orders AS a
    LEFT JOIN order_details AS b ON a.ID = b.OrderID
    LEFT JOIN order_routes AS d ON a.ID = d.OrderID
    LEFT JOIN (SELECT OrderID as OrderID2, COUNT(*) AS cnt FROM order_routes GROUP BY 1) AS d2 ON a.ID = d2.OrderID2
    LEFT JOIN userrate AS e ON e.ID = d.RouteID
    LEFT JOIN ratelist AS f ON f.ID = e.RateListID
    LEFT JOIN country AS g ON f.CountryID = g.ID
    LEFT JOIN network AS h ON f.NetworkID = h.ID
    WHERE a.UserID = 16 ORDER BY a.CreatedDate DESC