PostgreSQL时间戳和NULL的区别

Question

I'm novice in PostgreSQL. I have a column timestamp without time zone named FailureTime . At the beginning it has NULL value.

When SELECT I need to get all entries that has current_timestamp - FailureTime > interval '7' .

But when FailureTime is NULL the result of operation is NULL. Can I cast NULL to ZERO value or somehow get just current_timestamp as result of the operation?

Answer 1

current_timestamp - coalesce(FailureTime, current_timestamp) > interval '7'

Answer 2

You can exclude NULL elements by specifying something like:

SELECT ... 
WHERE (FailureTime IS NOT NULL) 
AND (current_timestamp - FailureTime > interval '7')