Informix SQL: How to get the date part of a datetime field in a query?

Question

What is the best way to use a only the date part of a datetime field in a query?
I have a datetime field and want to group/count it by date.

Answer 1

There are a number of ways of doing it:

EXTEND(dt_field, YEAR TO DAY)
CAST(dt_field AS DATETIME YEAR TO DAY)
dt_field::DATETIME YEAR TO DAY
CAST(dt_field AS DATE)
dt_field::DATE
DATE(dt_field)

The simplest - as in shortest - are the last two, and the function notation is probably clearest. The first three leave you with a DATETIME value; the last three leave you with a DATE value. These are similar, but not identical. They are fairly freely interchangeable though.

Answer 2

date(name_of_field)

Answer 3

This

to_char(dt_field, "%d %B %Y")

gives as 31 May 2016.

To group:

SELECT YEAR(dt_field) year, MONTH(dt_field) month, COUNT(*) count
FROM tblName
GROUP BY 1, 2
ORDER BY 1, 2;