Date comparisons
When working with timestamps, sometimes you want to find all observations on a given day. However, if you specify only a date in a comparison, you may get unexpected results. This query:
SELECT count(*)
FROM evanston311
WHERE date_created = '2018-01-02';
returns 0, even though there were 49 requests on January 2, 2018.
This is because dates are automatically converted to timestamps when compared to a timestamp. The time fields are all set to zero:
SELECT '2018-01-02'::timestamp;
2018-01-02 00:00:00
When working with both timestamps and dates, you'll need to keep this in mind.
Deze oefening maakt deel uit van de cursus
Exploratory Data Analysis in SQL
Praktische interactieve oefening
Probeer deze oefening eens door deze voorbeeldcode in te vullen.
-- Count requests created on January 31, 2017
SELECT count(*)
FROM evanston311
WHERE ___;