[英]How to compare records in same SQL Server table
我的要求是將行的每一列與其上一行進行比較。
另外,如果沒有區別,則需要將該列設置為NULL。 例如:第3行的request_status_id與第2行的相同,因此我需要將第3行的request_status_id更新為NULL。
有沒有一種干凈的方法可以做到這一點?
您可以使用下面的UPDATE
語句,該語句采用從SQL Server 2012起可用的LAG
窗口功能:
UPDATE #mytable
SET request_status_id = NULL
FROM #mytable AS m
INNER JOIN (
SELECT payment_history_id, request_status_id,
LAG(request_status_id) OVER(ORDER BY payment_history_id) AS prevRequest_status_id
FROM #mytable ) t
ON m.payment_history_id = t.payment_history_id
WHERE t.request_status_id = t.prevRequest_status_id
編輯:
似乎OP的要求是將表的每一列都SET
為NULL
,以防先前的值與當前值相同。 在這種情況下,查詢變得更加冗長。 這是設置兩個列的示例。 可以輕松地擴展它以合並表的任何其他列:
UPDATE #mytable
SET request_status_id = CASE WHEN t.request_status_id = t.prevRequest_status_id THEN NULL
ELSE T.request_status_id
END,
request_entity_id = CASE WHEN t.request_entity_id = t.prevRequest_entity_id THEN NULL
ELSE t.request_entity_id
END
FROM #mytable AS m
INNER JOIN (
SELECT payment_history_id, request_status_id, request_entity_id,
LAG(request_status_id) OVER(ORDER BY payment_history_id) AS prevRequest_status_id,
LAG(request_entity_id) OVER(ORDER BY payment_history_id) AS prevRequest_entity_id
FROM #mytable ) t
ON m.payment_history_id = t.payment_history_id
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