我想要合并两张桌子。第一个表是客户端,另一个是产品。目前我有22个产品,但我希望有一个灵活的数据库设计,所以在产品数据库中没有22列,每个客户每个产品有1行,所以如果我添加或删除1个产品,我不会必须改变数据库结构。
我想要一个select语句,我为每个客户选择所有产品,输出应该在一行中,每个产品都有一列。
我已经看到了一些类似的其他问题,但目标是将所有行连接在一列中 - 这是我不想要的。
假设有2个客户和3个产品。
表客户端:
ClientId | ClientName
---------------------
1 | Name1
2 | Name2
表产品
ProductId | ClientId | Product
-------------------------------------
1 | 1 | SomeproductA
2 | 1 | SomeproductB
3 | 1 | SomeproductA
4 | 2 | SomeproductC
5 | 2 | SomeproductD
6 | 2 | SomeproductA
输出应该是这样的:
表格输出:
ClientId | ClientName | Product1 | Product 2 | Product 3
-------------------------------------------------------------------
1 | Name1 | SomeproductA | SomeproductB | SomeproductA
2 | Name2 | SomeproductC | SomeproductD | SomeproductA
完美的解决方案也是灵活的,因为select语句应该计算每个客户端的不同产品的数量(对于所有客户端它们将始终是相同的),这样如果我为所有客户添加或删除1个产品客户端,我不应该更改select语句。
答案 0 :(得分:8)
MYSQL版
这是查询。联接查询使用User Defined Variables MySQL feature为每个客户端组内的每个产品生成RowNumber(1,2,3,...)。外部查询使用GROUP BY
形成PIVOT表,使用内部表中的行号形成CASE。如果您需要变量产品列数,请考虑创建此查询动态添加MAX(CASE WHEN p.RowNum=X THEN p.Product END) as ProductX
到选择列表。
select Clients.ClientName,
MAX(CASE WHEN p.RowNum=1 THEN p.Product END) as Product1,
MAX(CASE WHEN p.RowNum=2 THEN p.Product END) as Product2,
MAX(CASE WHEN p.RowNum=3 THEN p.Product END) as Product3,
MAX(CASE WHEN p.RowNum=4 THEN p.Product END) as Product4
FROM Clients
JOIN
(
SELECT Products.*,
if(@ClientId<>ClientId,@rn:=0,@rn),
@ClientId:=ClientId,
@rn:=@rn+1 as RowNum
FROM Products, (Select @rn:=0,@ClientId:=0) as t
ORDER BY ClientId,ProductID
) as P
ON Clients.ClientId=p.ClientId
GROUP BY Clients.ClientId
SQL Server Edition:
select Clients.ClientId,
MAX(Clients.ClientName),
MAX(CASE WHEN p.RowNum=1 THEN p.Product END) as Product1,
MAX(CASE WHEN p.RowNum=2 THEN p.Product END) as Product2,
MAX(CASE WHEN p.RowNum=3 THEN p.Product END) as Product3,
MAX(CASE WHEN p.RowNum=4 THEN p.Product END) as Product4
FROM Clients
JOIN
(
SELECT Products.*,
ROW_NUMBER() OVER (PARTITION BY ClientID ORDER BY ProductID)
as RowNum
FROM Products
) as P
ON Clients.ClientId=p.ClientId
GROUP BY Clients.ClientId
答案 1 :(得分:0)
答案似乎同时解决了 MySQL 和 SQL Server,所以我在这里添加了一个进一步的 SQL Server 答案,该逻辑也可能适用于 MySQL。
以下是用于 MS SQL Server 的 Transact SQL 中的动态 SQL 版本。
这使您能够获得相同的结果,而不必像 CASE WHEN 解决方案那样在结果表中明确写出您需要的每一列。 CASE WHEN 对几列来说既简单又好用,但我最近有一个类似的场景,它可以旋转到大约 200 列。
对于动态 SQL,您本质上是使用生成的变量将所需的查询编译为字符串,然后执行它。
-- variable tables to store data
DECLARE @Clients TABLE(ClientID int,
ClientName nvarchar(10))
DECLARE @Products TABLE(ProductID int,
ClientID int,
Product nvarchar(15))
-- populate the variable tables with sample data
INSERT INTO @Clients
VALUES (1, 'Name1'),
(2, 'Name2')
INSERT INTO @Products
VALUES (1, 1, 'SomeproductA'),
(2, 1, 'SomeproductB'),
(3, 1, 'SomeproductA'),
(4, 2, 'SomeproductC'),
(5, 2, 'SomeproductD'),
(6, 2, 'SomeproductA')
-- display the tables to check
SELECT * FROM @Clients
SELECT * FROM @Products
-- join the two tables and generate a column with rows which will become the new
-- column names (Product_col) which gives a number to each product per client
SELECT c.ClientID,
c.ClientName,
p.ProductID,
p.Product,
CONCAT('Product', ROW_NUMBER()
OVER(PARTITION BY c.ClientID ORDER BY p.Product ASC)) AS Product_col
INTO #Client_Products
FROM @Products p
LEFT JOIN @Clients c ON c.ClientID = p.ClientID
-- view the joined data and future column headings
SELECT * FROM #Client_Products
-- setup for the pivot, declare the variables to contain the column names for pivoted
-- rows and the query string
DECLARE @cols1 AS NVARCHAR(MAX),
@query AS NVARCHAR(MAX);
-- column name list for products
SET @cols1 = STUFF((SELECT distinct ',' + QUOTENAME(Product_col)
FROM #Client_Products
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
SELECT @cols1 -- view the future column names
-- generate query variable string
-- the top select is all the columns you want to actually see as the result
-- The inner query needs the columns you want to see in the result, and the columns
-- you are pivoting with. The pivot needs to select the value you want to go into the
-- new columns (MAX()) and the values that will become the column names (FOR x IN())
SET @query = 'SELECT ClientID,
ClientName,'
+ @cols1 +'
FROM
(
SELECT ClientID,
ClientName,
Product_col,
Product
FROM #Client_Products
) x
PIVOT
(
MAX(Product)
FOR Product_col IN (' + @cols1 + ')
) p'
EXECUTE(@query) -- execute the dynamic sql
DROP TABLE #Client_Products