Thanks for the reply,
There are no joins, its just a single table.
Can you share screenshot of what you have & how you are taking these tables. As, I do not think that there is any issue with Tableau. Also, drag & drop [Number of Records] field into sheet & check the total number of records.
Well if you don't have any joins and directly dragging and droping the sheet then I am pretty much sure the data will reflect as in your database, May be you can check the "postgre sql" it may be giving you wrong number..
otherwise as mentioned by Prashant a screen shot is always helpful.