[英]Sql return empty cell in subquery
我有兩個表:
transfers
| No_ | PostingDate | Code |
comments
| No_ | comment |
一次轉移可以有很多評論。
我需要創建一個查詢,該查詢返回所有轉賬以及其注釋中的前1條注釋,如果沒有注釋,則為空注釋。
SELECT
th.[No_],
th.[Posting Date] as 'PostingDate',
th.[Transfer-to Code] as 'Transfer_To',
icl.Comment
FROM
dbo.[company$Transfer Header] as th,
dbo.[company$Inventory Comment Line] as icl
where
th.No_=icl.No_
我有這個,但它只返回帶有注釋的傳輸。
我該如何退回所有轉賬,如果轉賬沒有評論,則返回空評論。
將LEFT JOIN
和COALESCE
一起用空注釋替換缺少的NULL
值:
SELECT th.[No_], th.[Posting Date] as 'PostingDate',
th.[Transfer-to Code] as 'Transfer_To',
COALESCE(icl.Comment, '')
FROM
dbo.[company$Transfer Header] AS th
LEFT JOIN
dbo.[company$Inventory Comment Line] AS icl
ON th.No_ = icl.No_
我可能傾向於使用outer apply
:
SELECT th.[No_], th.[Posting Date] as PostingDate,
th.[Transfer-to Code] as Transfer_To,
COALESCE(icl.Comment, '') as Comment
FROM dbo.[company$Transfer Header] as th OUTER APPLY
(SELECT TOP 1 icl.*
FROM dbo.[company$Inventory Comment Line] icl
WHERE th.No_ = icl.No_
) icl;
這假定您要一個注釋,並且當沒有注釋時,您需要一個空字符串。
筆記:
ORDER BY
子句,但尚不清楚如何選擇一個注釋。 JOIN
語法。
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