Sql Server 2008 - 没有聚合功能的PIVOT

Question

我知道你有多个主题涉及到这一点.但是,我找不到满足我需求的.我需要(按需)将深度表数据透视到宽输出表.这里的问题是我不能使用Pivot的聚合,因为它会占用输出中需要的响应.我已经找到了解决方案,但我认为这不是最好的,因为它需要无数的左连接才能工作.我已将所有尝试和说明包括在内如下:

-- Sql Server 2008 db.
-- Deep table structure (not subject to modification) contains name/value pairs with a userId as
-- foreign key.  In many cases there can be MORE THAN ONE itemValue given by the user for the
-- itemName such as if asked their race, can answer White + Hispanic, etc.  Each response is stored
-- as a seperate record - this cannot currently be changed.

-- Goal: pivot deep data to wide while also compressing result 
-- set down. Account for all items per userId, and duplicating
-- column values (rather than show nulls) as applicable

-- Sample table to store some data of both single and multiple responses
DECLARE @testTable AS TABLE(userId int, itemName varchar(50), itemValue varchar(255))

INSERT INTO @testTable
SELECT 1, 'q01', '1-q01 Answer'
UNION SELECT 1, 'q02', '1-q02 Answer'
UNION SELECT 1, 'q03', '1-q03 Answer 1'
UNION SELECT 1, 'q03', '1-q03 Answer 2'
UNION SELECT 1, 'q03', '1-q03 Answer 3'
UNION SELECT 1, 'q04', '1-q04 Answer'
UNION SELECT 1, 'q05', '1-q05 Answer'
UNION SELECT 2, 'q01', '2-q01 Answer'
UNION SELECT 2, 'q02', '2-q02 Answer'
UNION SELECT 2, 'q03', '2-q03 Answer 1'
UNION SELECT 2, 'q03', '2-q03 Answer 2'
UNION SELECT 2, 'q04', '2-q04 Answer'
UNION SELECT 2, 'q05', '2-q05 Answer'

SELECT 'Raw Data'
SELECT * FROM @TestTable

SELECT 'Using Pivot - shows aggregate result of itemValue per itemName - eats others'
; WITH Data AS (
    SELECT
        [userId]
        , [itemName]
        , [itemValue]
    FROM 
        @testTable
)
SELECT
    [userId]
    , [q02]
    , [q03]
    , [q05]
FROM
    Data
PIVOT
(
    MIN(itemValue)  -- Aggregate function eats needed values.
    FOR itemName in ([q02], [q03], [q05])
) AS PivotTable


SELECT 'Aggregate with Grouping - Causes Null Values'
SELECT
    DISTINCT userId 
    ,[q02] = Max(CASE WHEN itemName = 'q02' THEN itemValue END)
    ,[q03] = Max(CASE WHEN itemName = 'q03' THEN itemValue END)
    ,[q05] = Max(CASE WHEN itemName = 'q05' THEN itemValue END)
FROM
    @testTable
WHERE
    itemName in ('q02', 'q03', 'q05')   -- Makes it a hair quicker
GROUP BY
    userId  -- If by userId only, it only gives 1 row PERIOD = BAD!!
    , [itemName]
    , [itemValue]


SELECT 'Multiple Left Joins - works properly but bad if pivoting 175 columns or so'
; WITH Data AS (
    SELECT
        userId 
        ,[itemName]
        ,[itemValue]
    FROM
        @testTable
    WHERE
        itemName in ('q02', 'q03', 'q05')   -- Makes it a hair quicker
)
SELECT
    DISTINCT s1.userId
    ,[q02] = s2.[itemValue]
    ,[q03] = s3.[itemValue]
    ,[q05] = s5.[itemValue]
FROM
    Data s1
    LEFT JOIN Data s2 
        ON s2.userId = s1.userId 
            AND s2.[itemName] = 'q02'
    LEFT JOIN Data s3 
        ON s3.userId = s1.userId 
            AND s3.[itemName] = 'q03'
    LEFT JOIN Data s5 
        ON s5.userId = s1.userId 
            AND s5.[itemName] = 'q05'

因此,底层查询是唯一一个(到目前为止)执行我需要它做的事情,但是当我使用实际项目名称进行转动时,LEFT JOIN将失控并导致性能问题.任何建议表示赞赏.

Answer 1

; 将 SRData 作为 (
    SELECT——仅查询该块中的单个响应项
        [用户身份]
        , [q01]
        , [q02]
        , [q04]
        , [q05]
    从
        @测试表
    枢
    （
        MIN(项目值)
        FOR itemName in ([q01], [q02], [q04], [q05])
    ) AS 数据透视表
）
选择
    sr.[用户 ID]
    ，老先生。[q01]
    ，老先生。[q02]  
    , [q03] = mr03.[项目值]
    ，老先生。[q04]      
    ，老先生。[q05]      
    , [q06] = mr06.[项目值]
从
    SR数据SR
    LEFT JOIN @testTable mr03 ON mr03.userId = sr.userId AND mr03.itemName = 'q03' -- Muli 响应 q03
    LEFT JOIN @testTable mr06 ON mr06.userId = sr.userId AND mr06.itemName = 'q06' -- Muli 响应 q06