[英]Combining Data From Multiple Rows
我有3個表要編寫查詢:Memos,Memos_Description,策略。 該數據庫不是我自己設計的,我無法更改它,這只是一個報告。
我目前有一個查詢似乎正在運行,但在加入所需的額外表之前效率極低。
SELECT
Main.CLIENTSNAME,
Main.ENTRYDATE,
Main.AUTHOR,
Main.POLICYNUMBER,
Main.CLIENTS_ID,
Main.MEMOS_ID,
Left(Main.DESCRIPTION,Len(Main.DESCRIPTION)) AS REGARDING
FROM
(
SELECT distinct ST1.MEMOS_ID,
(
SELECT ST2.DESCRIPTION + ' ' AS [text()]
FROM dbo.MEMOS_DESCRIPTION ST2
WHERE ST1.MEMOS_ID = ST2.MEMOS_ID
ORDER BY ST1.MEMOS_ID
For XML PATH ('')
) [DESCRIPTION],
ST1.CLIENTSNAME,
ST1.ENTRYDATE,
ST1.AUTHOR,
ST1.POLICYNUMBER,
ST1.REGARDING,
ST1.CLIENTS_ID
FROM dbo.MEMOS ST1
) [Main]
這些表如下所示:
tbl.MEMOS
MEMOS_ID
POLICIES_ID
CLIENTSNAME
tbl.MEMOS_DESCRIPTION
MEMOS_ID
DESCRIPTION
tbl.POLICIES
POLICIES_ID
POLICYNUMBER
數據如下所示:
tbl1.MEMOS_ID | tbl1.CLIENTSNAME
1 PERSON ONE
2 PERSON TWO
3 PERSON THREE
tbl2.MEMOS_ID | tbl2.DESCRIPTION
1 This is a sentence
1 that can run over more
1 than one description record.
2 Person two has
2 something different.
3 Client Created.
tbl3.POLICIES_ID | tbl3.POLICYNUMBER
123 ABCDE
456 FGHIJ
我希望報告看起來像:
tbl1.MEMOS_ID | tbl1.CLIENTSNAME | tbl2.DESCRIPTION | tbl3.POLICIES_ID | tbl3.POLICYNUMBER
1 PERSON ONE This is a sentence that can run over more tan one description record. 123 ABCDE
我希望這是有道理的,謝謝。
根據戈登的建議答案更新了查詢:
SELECT ST1.*,
STUFF(
(SELECT ' ' + ST2.DESCRIPTION AS [text()]
FROM dbo.MEMOS_DESCRIPTION ST2
WHERE ST1.MEMOS_ID = ST2.MEMOS_ID
ORDER BY ST1.MEMOS_ID
For XML PATH ('')
), 1, 1, '') [REGARDING]
FROM
(SELECT DISTINCT ST1.MEMOS_ID,
ST1.CLIENTSNAME,
ST1.ENTRYDATE,
ST1.AUTHOR,
ST1.POLICYNUMBER,
ST1.CLIENTS_ID,
ST1.POLICIES_ID
FROM dbo.MEMOS ST1
) ST1
LEFT JOIN POLICIES B
ON ST1.POLICIES_ID = B.POLICIES_ID
WHERE ST1.ENTRYDATE >= DATEADD(month, -2, GETDATE())
AND (B.PROD1 = ('123') OR B.PROD1 = ('456') OR B.PROD1 = ('789'))
如果您在進行字符串聚合之前 select distinct
,那么性能如何比較?
SELECT ST1.*,
STUFF((SELECT ' ' + ST2.DESCRIPTION AS [text()]
FROM dbo.MEMOS_DESCRIPTION ST2
WHERE ST1.MEMOS_ID = ST2.MEMOS_ID
ORDER BY ST1.MEMOS_ID
For XML PATH ('')
), 1, 1, '') ) [DESCRIPTION]
FROM (SELECT DISTINCT T1.MEMOS_ID, ST1.CLIENTSNAME, ST1.ENTRYDATE,
ST1.AUTHOR, ST1.POLICYNUMBER, ST1.REGARDING, ST1.CLIENTS_ID
FROM dbo.MEMOS ST1
) ST1
我懷疑SQL Server可能在運行不同的行之前對每一行進行字符串聚合-這是很多不必要的工作。
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