每个组的 MAX 的 SQL

Question

我有 4 张桌子。我试图为每个汽车品牌获得最大价值。有10个品牌。我想知道每个品牌哪辆车最贵。

我做的第一件事是将所有我想从中获取信息的表格分组。 我已经加入了 BRAND、MODEL、CLASS 和 VEH 表。但是，我不确定如何获得每个组的最大值。

SELECT B.BRAND_NAME, M.MODEL_NAME, C.CLASS_NAME, V.VEH_YEAR,  V.VEH_PRICE

FROM ((VEHICLE V INNER JOIN CLASS C ON V.CLASS_ID = C.CLASS_ID)
INNER JOIN MODEL M ON M.MODEL_ID = V.MODEL_ID)
INNER JOIN BRAND B ON B.BRAND_ID = M.BRAND_ID

我试过了：

SELECT B.BRAND_NAME, M.MODEL_NAME, C.CLASS_NAME, V.VEH_YEAR,  V.VEH_PRICE
FROM (
SELECT B.BRAND_NAME, MAX(V.VEH_PRICE)
FROM ((VEHICLE V INNER JOIN CLASS C ON V.CLASS_ID = C.CLASS_ID)
INNER JOIN MODEL M ON M.MODEL_ID = V.MODEL_ID)
INNER JOIN BRAND B ON B.BRAND_ID = M.BRAND_ID
GROUP BY B.BRAND_NAME
);

我得到：

Answer 1

如果您只想要每个品牌的最高车辆价格，您的加入就可以了。它只需要一个GROUP BY 和MAX() 函数（请注意，您不需要Class 表）：

SELECT B.BRAND_NAME, 
       MAX(V.VEH_PRICE) AS MAX_VEH_PRICE

FROM ( VEHICLE V
  INNER JOIN MODEL M ON M.MODEL_ID = V.MODEL_ID )
  INNER JOIN BRAND B ON B.BRAND_ID = M.BRAND_ID

GROUP BY B.BRAND_ID, B.BRAND_NAME ;

要获取价格最高的车辆的所有车辆数据，您需要在子查询（派生表）中编写上一个查询，然后再次连接：

SELECT B.BRAND_NAME, M.MODEL_NAME, C.CLASS_NAME, V.VEH_YEAR,  V.VEH_PRICE

FROM  
    ( ((VEHICLE V INNER JOIN CLASS C ON V.CLASS_ID = C.CLASS_ID)
      INNER JOIN MODEL M ON M.MODEL_ID = V.MODEL_ID)
      INNER JOIN BRAND B ON B.BRAND_ID = M.BRAND_ID
    )

  INNER JOIN

    ( SELECT M.BRAND_ID, 
             MAX(V.VEH_PRICE) AS VEH_PRICE  
      FROM (VEHICLE V
        INNER JOIN MODEL M ON M.MODEL_ID = V.MODEL_ID)
      GROUP BY M.BRAND_ID 
    ) AS derived

    ON  b.BRAND_ID = derived.BRAND_ID
    AND v.VEH_PRICE = derived.VEH_PRICE ;