As you can see, I select a date. So in December, the date will be: BETWEEN '201612015' AND '201601015', for example.
That is an unusual timestamp value...what's the 5 for? (I've figured this out...but its still unusual)
1. Why when I run the function manually I get this error?
select logextract(201612015, 201612015);
ERROR: operator does not exist: timestamp without time zone >= integer
LINE 13: BETWEEN
I presume this is wrong: CREATE or REPLACE FUNCTION logextract(date_start integer, date_end integer) - But what should I use instead?
I don't understand why "date" wouldn't be your first choice here. Or, better yet, a single argument of type daterange.
2. To call the function, I have to login to postgres and then run: select logextract(201612015, 201612015); How can I do it on cron? because the dates will be different every time.
PostgreSQL knows what the current date is so describe how to compute your desired boundaries given a single date.
Dates and times are their own types in PostgreSQL. They are incompatible with integers. You either to convert one or the other if you want to perform a comparison.
