When you design your table, you choose to add a primary key constraint for one or more column while create the same. Column attached with primary key constraint should contain UNIQUE and NOT NULL values. We all know that. But PostgreSQL does not force this constraint while creating a new table, you might forget to add one (missing morning coffee may be). I tried creating a table without adding primary key constraint in PostgreSQL CREATE TABLE weather ( city character varying(80), temp_lo integer, temp_hi integer, prcp real, date date ); This took off and created the weather table successfully. Now when I tried to view data (which I inserted after creating the table) using pgAdmin III, it displayed hint (warning, I would say) as Edit table data without primary key This warning message say, I will not be able to edit or change existing row data since I do » Read more