SQL：While 和 Union 来统一 SELECT

Question

让我们试试这个方法。

如您所见，我有很多 SELECT（我只展示了 3 个，但我有 20 多个），我需要统一所有这些。每次我需要添加一个品牌时，我都必须一个一个地更改所有的选择。这很无聊。

另外，我有超过 10 个品牌（不仅仅是 3 个），我也需要一一输入。如果我可以只更改 1 次并让 WHILE LOOP 为其他 SELECT 完成其余的工作，这还不错。但是，如果我必须为所有 SELECT 更改所有品牌，我会花费很多时间。

DECLARE @COUNTRY varchar(30)
SET @COUNTRY = 'GERMANY'

SELECT * FROM
(SELECT * FROM
    (SELECT
        FOOD_CATEGORY,
        YEAR_SALE,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND A' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3) 
        END AS Share_A,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND B' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_B,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND C' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_C
    FROM tableChicken
    WHERE
        AREA = @COUNTRY
    GROUP BY
        FOOD_CATEGORY,
        YEAR_SALE) AS CHICKEN

UNION

SELECT * FROM

    (SELECT
        FOOD_CATEGORY,
        YEAR_SALE,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND A' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3) 
        END AS Share_A,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND B' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_B,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND C' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_C
    FROM tableSwine
    WHERE
        AREA = @COUNTRY
    GROUP BY
        FOOD_CATEGORY,
        YEAR_SALE) AS SWINE

UNION

SELECT * FROM

    (SELECT
        FOOD_CATEGORY,
        YEAR_SALE,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND A' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3) 
        END AS Share_A,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND B' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_B,
        CASE WHEN SUM(SALES)=0 THEN 0
        ELSE ROUND(SUM(CASE WHEN FABRICANTE='BRAND C' THEN ROUND(SALES,3) ELSE 0 END)/SUM(SALES),3)
        END AS Share_C
    FROM tableTurkey
    WHERE
        AREA = @COUNTRY
    GROUP BY
        FOOD_CATEGORY,
        YEAR_SALE) AS TURKEY
) AS MAIN_BASE

ORDER BY FOOD_CATEGORY, YEAR_SALE

我希望现在可以理解了。感谢您的帮助！

Answer 1

我知道这是您的代码的简单版本，但您不能这样做。

SELECT Brand
     , SUM(Sales_Kg)  AS Sales_Volume
FROM tblSales
WHERE Year = 2015 
  and ID_Brand IN (1,2,3)  -- ADD THIS LINE
GROUP BY Brand

我真的不明白为什么当group by 已经设置了brand_id 时，你用CASE 使查询复杂化

否则使用临时表保存每个结果SAMPLE

Answer 2

我觉得逻辑很奇怪，但你可以使用cross join：

SELECT Brand,
       (CASE WHEN SUM(Sales_Kg)=0 THEN 0
             ELSE SUM(CASE WHEN ID_Brand = b.id_brand THEN Sales_Kg ELSE 0 END)  
        END) AS Sales_Volume
FROM tblSales s CROSS JOIN
     (SELECT 1 as id_brand UNION ALL SELECT 2 UNION ALL select 3) b
WHERE Year = 2015
GROUP BY Brand, b.id_brand;

您可能还想在select 中包含b.id_brand。