sql - 强制 Count 中出现零

Question

以下代码采用一个包含车辆名称的表和一个包含区域名称的表，并将它们组合成一个结果表。 然后，我对结果表执行 COUNT 操作，以显示每个区域有多少车辆。

我需要修改代码以强制计算所有区域和所有车辆。目前，COUNT 语句不显示任何不包含车辆的区域(我已从结果中手动删除了一些条目以显示这一点)。谁能说明一种快速的方法来做到这一点？我正在使用 SQL 2012，希望有一个简单的解决方案...

为了回答问题，请假设两个原始表不再可访问，并且我们现在仅使用@tbl_results。谢谢。

注意:我知道我可以直接从车辆和区域表中执行此操作，但我需要在实际工作中为其他流程使用结果表变量。

DECLARE @tbl_vehicles TABLE (vehicleID int, vehicleName nvarchar(100))
DECLARE @tbl_regions TABLE (regionID int, regionName nvarchar(100))
DECLARE @tbl_results TABLE (regionID int, regionName nvarchar(100), vehicleID int, vehicleName nvarchar(100))

INSERT INTO @tbl_regions (regionID, regionName) VALUES (1, 'England')
INSERT INTO @tbl_regions (regionID, regionName) VALUES (2, 'United States')
INSERT INTO @tbl_regions (regionID, regionName) VALUES (3, 'Arctic')

INSERT INTO @tbl_vehicles (vehicleID, vehicleName) VALUES (1, 'Planes')
INSERT INTO @tbl_vehicles (vehicleID, vehicleName) VALUES (2, 'Trains')
INSERT INTO @tbl_vehicles (vehicleID, vehicleName) VALUES (3, 'Automobiles')

DECLARE @i INT
SET @i = 0 

WHILE @i < 100
    BEGIN
        INSERT INTO @tbl_results
            (regionID, regionName, vehicleID, vehicleName) 
        SELECT
            r.regionID, r.regionName, v.vehicleID, v.vehicleName 
        FROM
            @tbl_regions r CROSS JOIN
            @tbl_vehicles v 
        WHERE
            (r.regionID = CAST(RAND() * 4 AS INT)) AND
            (v.vehicleID = CAST(RAND() * 4 AS INT)) 
        SET @i = @i + 1
    END

-- remove trains in the arctic for count example
DELETE FROM @tbl_results WHERE (regionID=3) AND (vehicleID=2)

-- this statement needs to include ALL vehicles and ALL regions (even if no vehicles are found at a region)
SELECT 
    regionName,
    vehicleName,
    COUNT(*) as VehicleCount
FROM
    @tbl_results 
GROUP BY
    regionID,
    regionName,
    vehicleID,
    vehicleName
ORDER BY regionName, vehicleName  

Answer 1

SELECT  r.regionName
,       v.vehicleName
,       COUNT(res.vehicleName) as VehicleCount
FROM    (
        select  distinct regionName
        from    @tbl_results
        ) r
CROSS JOIN 
        (
        select  distinct vehicleName
        from    @tbl_results
        ) v
LEFT OUTER JOIN
        @tbl_results res
ON      r.regionName = res.regionName
        AND v.vehicleName = res.vehicleName
GROUP BY
        r.regionName
,       v.vehicleName
ORDER BY
        r.regionName
,       v.vehicleName