Question

I’m trying (SQL Server Compact) to add primary key constraint on existing table that has some rows in it. While adding primary key I’m getting the error:

“A duplicate key cannot be inserted into a unique index”

I don’t what this is, can anyone help me with this?

Answer 1

Try this

select id_column, count(*) from your_table group by id_column having count(*) > 1

If there are any records returned from this above query you cannot add a primary key on id_column since duplicate IDs exist.

Of course you will need to replace id_column and your_table with the appropriate names.