Difference of timestamp event rows using WHERE clause - sql

Question

I have two event tables with timestamped data: Registered, Signed_In.
Both have rows such as: original_timestamp, user_id
I am trying to find out users who haven't signed in within 30 days after registering. I have used the following query but I cannot add a WHERE clause to it.
I tried a query but I am getting hourly difference, whereas I wanted days difference which is unsupported in BigQuery.
SELECT Signed_In.user_id, TIMESTAMP_DIFF(Registered.original_timestamp, Signed_In.original_timestamp, HOUR) AS days_difference
FROM `test_db.Signed_In` signed_in
JOIN `test_db.Registered` registered
ON Signed_In.user_id = Registered.user_id
GROUP BY 1,2
ORDER BY 2 DESC
WHERE days_difference > '30'
I am getting two columns: user_id, days_difference but the days_difference shows hours and my WHERE clause is rejected when I use it.

Answer 1

You can try this below code-
Note: Using Ordinal Position for GROUP BY and ORDER BY is not a good practice. Its always safe and standard to use the column names directly.
SELECT Signed_In.user_id,
TIMESTAMP_DIFF(Registered.original_timestamp, Signed_In.original_timestamp, HOUR) AS days_difference
FROM `test_db.Signed_In` signed_in
JOIN `test_db.Registered` registered
ON Signed_In.user_id = Registered.user_id
WHERE DATE_DIFF(Registered.original_timestamp, Signed_In.original_timestamp, Day) > '30'
GROUP BY 1,2
ORDER BY 2 DESC

Answer 2

Just replace HOUR to DAY in your query:
SELECT Signed_In.user_id, TIMESTAMP_DIFF(Registered.original_timestamp, Signed_In.original_timestamp, DAY) AS days_difference
Correct values are:
MICROSECOND
MILLISECOND
SECOND
MINUTE
HOUR
DAYOFWEEK
DAY
DAYOFYEAR
WEEK: Returns the week number of the date in the range [0, 53]. Weeks begin with Sunday, and dates prior to the first Sunday of the year are in week 0.
WEEK(<WEEKDAY>): Returns the week number of timestamp_expression in the range [0, 53]. Weeks begin on WEEKDAY. datetimes prior to the first WEEKDAY of the year are in week 0. Valid values for WEEKDAY are SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY.
ISOWEEK: Returns the ISO 8601 week number of the datetime_expression. ISOWEEKs begin on Monday. Return values are in the range [1, 53]. The first ISOWEEK of each ISO year begins on the Monday before the first Thursday of the Gregorian calendar year.
MONTH
QUARTER
YEAR
ISOYEAR: Returns the ISO 8601 week-numbering year, which is the Gregorian calendar year containing the Thursday of the week to which date_expression belongs.
DATE
DATETIME
TIME