Question

我有一个统计查询，它将返回三行（因为我有3种类型，我按其分组），我也知道行的顺序，因为我明确ORDER BY FIELD：

SELECT COUNT(id) AS c FROM Vehicles GROUP BY VehicleTypeID ORDER BY FIELD(VehicleTypeID, 1,2,3)

有没有一种简单的方法将行转换为列？类似（PSEUDO SQL）：

SELECT c[0] AS CarsCount, c[1] AS MotorcyclesCount, c[2] AS TrucksCount FROM (
     SELECT COUNT(id) AS c 
     FROM Vehicles 
     GROUP BY VehicleTypeID 
     ORDER BY FIELD(VehicleTypeID, 1,2,3)
)

Answer 1

是的，它是带有聚合的case语句：

SELECT max(case when fieldnum = 1 then c end) AS CarsCount, 
       max(case when fieldnum = 2 then c end) AS MotorcyclesCount, 
       max(case when fieldnum = 3 then c end) AS TrucksCount
FROM (SELECT COUNT(id) AS c , FIELD(VehicleTypeID, 1,2,3) as fieldnum
      FROM Vehicles 
      GROUP BY VehicleTypeID 
     ) t;

将简单的单列3行结果转换为单行，3列结果？

1 个答案: