SQL Server 2008:删除重复的行

Question

我的表中有重复的行,如何根据单个列的值删除它们？

例如

uniqueid, col2, col3 ...
1, john, simpson
2, sally, roberts
1, johnny, simpson

delete any duplicate uniqueIds
to get 

1, John, Simpson
2, Sally, Roberts

Answer 1

你可以DELETE从cte:

WITH cte AS (SELECT *,ROW_NUMBER() OVER(PARTITION BY uniqueid ORDER BY col2)'RowRank'
             FROM Table)
DELETE FROM cte 
WHERE RowRank > 1

该ROW_NUMBER()函数为每一行分配一个数字. PARTITION BY用于为该组中的每个项目开始编号,在这种情况下,每个值uniqueid将从1开始编号并从那里开始. ORDER BY确定数字进入的顺序.由于每个uniqueid数字从1开始编号,任何ROW_NUMBER()大于1的记录都有重复uniqueid

要了解ROW_NUMBER()函数的工作原理,请尝试一下:

SELECT *,ROW_NUMBER() OVER(PARTITION BY uniqueid ORDER BY col2)'RowRank'
FROM Table
ORDER BY uniqueid

您可以调整ROW_NUMBER()函数的逻辑以调整要保留或删除的记录.

例如,您可能希望通过多个步骤执行此操作,首先删除具有相同姓氏但名字不同的记录,您可以将姓氏添加到PARTITION BY:

WITH cte AS (SELECT *,ROW_NUMBER() OVER(PARTITION BY uniqueid, col3 ORDER BY col2)'RowRank'
             FROM Table)
DELETE FROM cte 
WHERE RowRank > 1