Why returns this query 'date_parse(Openingsdatum, '%d-%m-%Y' )' more information then just the day, month and year ?

It is an expected output from date_parse which "parses timestamps"/"returns a timestamp" please follow this presto documentation : https://prestodb.io/docs/current/functions/datetime.html#mysql-date-functions.

You can use this query to truncate the time part from timestamp.

select Date(date_parse('2022-03-01','%Y-%m-%d'))

Also please note that Athena for DML queries uses presto for query execution. So in order to write a DML query upto Athena standards we have to use presto functions only.

Here date_parse() expects a string argument and parses that into timestamp format. Now as you stated that you also have null values. Here I have one question, are these empty values is in the form of "" or null in your table, Because if the empty values are in the form of 'null' then the date_parse should work perfectly fine. Like below:

select Date(date_parse(null,'%Y-%m-%d'))

But this will not :

select Date(date_parse('','%Y-%m-%d'))

because on seeing string '' it performs parsing only to find it is not in the standard format and throws error INVALID_FUNCTION_ARGUMENT: Invalid format: ""

In order to make it work you can use this query

select CASE date_g
           WHEN '' THEN null
           ELSE Date(date_parse(date_g,'%Y-%m-%d'))
       END 
FROM Table_name