Select row if column data was not selected How can I selected rows from a table when a column data is different.

Table: id(pk), name, title, book_id, date

I want to get all the rows where book_id is uniq.

Data example:

test1, test2, 1, 2015-01-01
test2, test4, 1, 2015-01-02
test2, test3, 1, 2015-01-02
test2, test2, 4, 2015-01-03
test4, test2, 5, 2015-01-04
test5, test2, 5, 2015-01-05


Expected output:

test1, test2, 1, 2015-01-01
test2, test3, 1, 2015-01-02
test2, test2, 4, 2015-01-03
test4, test2, 5, 2015-01-04
This can easily be done using Postgres' distinct on operator:

select distinct on (book_id) name, title, bookd_id, date
from the_table
order by book_id, date;


This will pick the first row for each book_id based on the date column.