Peter Eisentraut wrote:
David Inglis wrote:
Can anybody assist with this problem I have a table that has some
duplicated rows of data, I want to place a unique constraint on the
columns userid and procno to eliminate this problem in the future but
how do I identify and get rid of the existing duplication.
To find them, something like
SELECT a, b, c FROM table GROUP BY a, b, c HAVING count(*) > 1;
comes to mind, where you have to list all columns of the table in place
of a, b, c.
As for deleting all but one row in a duplicated group, you're going to
have to get at them by the oid or ctid columns perhaps.
The other idea is to run CREATE TABLE newtable AS SELECT DISTINCT * FROM
oldtable;.
This doesn't bring over to the new table any foreign key relationships
or triggers.
Another approach (if you don't have OID's) is to create uniqueness by
appending a column to the table, populating it with sequential integers.
Then you proceed as otherwise suggested above by using aggregation to
identify the duplicated rows.
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