Updating duplicate records in same table

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SQL-Server-2008

I have a table named "Table1"
Its schema with data is like this

Id | col2 | col3 | col4 | col5 | isUnique | dbUnique
1 | red | 3M | 1995 | UK | 1 | null
2 | red | 3M | 1995 | UK | 0 | null
2 | red | 3M | 1995 | UK | 0 | null
3 | red | 3M | 1995 | UK | 0 | null
4 | pink | A4 | 2002 | USA | 1 | null
5 | pink | A4 | 2002 | USA | 0 | null

Now my question is that, that i want to update dbUnique column of this table, such that dbUnique should contain Id of Table1 where isUnique is 1 in all duplicate rows based on col2,col3,col4 & col5

So my updated data will look like this

Id | col2 | col3 | col4 | col5 | isUnique | dbUnique
1 | red | 3M | 1995 | UK | 1 | 1
2 | red | 3M | 1995 | UK | 0 | 1
2 | red | 3M | 1995 | UK | 0 | 1
3 | red | 3M | 1995 | UK | 0 | 1
4 | pink | A4 | 2002 | USA | 1 | 4
5 | pink | A4 | 2002 | USA | 0 | 4

this table has over 50,000 rows.

How can i do this in MS SQL 2008

Posted 16-Jun-11 3:06am

markand911

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Maciej Los · Answer 1 · 2011-06-21T05:41:00

If Id is unique value, like this:

MIDL

Id | col2 | col3 | col4 | col5 | isUnique | dbUnique
1 | red | 3M | 1995 | UK | 1 | null
2 | red | 3M | 1995 | UK | 0 | null
3 | red | 3M | 1995 | UK | 0 | null
4 | red | 3M | 1995 | UK | 0 | null
5 | pink | A4 | 2002 | USA | 1 | null
6 | pink | A4 | 2002 | USA | 0 | null

(not: 1, 2, 2, 3, 4, 5) the fallowing instruction:

SQL

SELECT col2, Count(col2) AS CountOfCol2, Min(ID) AS MinOfID
FROM Table1
GROUP BY col2
HAVING (Count(col2)>1);

returns:

col2 | CountOfCol2 | MinOfID<br />
pink | 2 | 5<br />
red | 4 | 1<br />

So you need to build another instructions to update your table using data returned by previous instruction.
I'm not sure which column is grouping column, so i can't help you more.