Unique contraints cause duplicate fields when using postgres

[jhartwell]

If you have a column that is a primary key and also has a unique constraint that column will be exported twice in the output. We don't need to worry about the unique constraint so it will need to be ignored

[tomjoro]

I have traced the issue and have a fix for it (I can make a pull request). The issue is caused by this left join:

        LEFT JOIN pg_index i ON
            (pgc.oid = i.indrelid AND i.indkey[0] = a.attnum)

This causes two effects:

1. Compound primary keys don't work
2. If the field is repeated in another index you will get a row for both primary_key: true and primary_key: false (which now generates the field twice).

The solution I have is just to query the primary key(s) in another query otherwise the SQL gets too complicated.