query for non-unique values?

Andy Kriger wrote:

I have a file of legacy data that has duplicate entries in a column that I'd
like to have a unique index on. How can I query to find the duplicates (so I
can determine if they can be thrown out)?

If you have yet to learn about self joins, this is a great example of
where they are handy. Assuming a table like:

create table abc
(
id int not null, -- primary key
name text, -- duplicates are here
);

Try something like:

select b.*
from abc a, abc b
where a.id < b.id
and a.name = b.name;

HTH,
Kevin

select dup_columns,count((*)
from table
group by dup_columns
having count(*) > 1