Calculating difference of dates In Postgresql

问题

I'm trying to find out the time between certain fields in my tables. However cause I'm using Postgresql :(( I can't use the DATEDIFF function. I can't find any clear guides/ tutorials on the net which shows how to do a similar thing in Postgres so I need help doing the same thing but in Postgres

I'm assuming this query would work if I was using a RDBMS that supported the DATEDIFF function so basically my question is how can I change this so it works using features provided by Postgresql?

SELECT Question.ID, 
Question.Status, COUNT (qUpdate.ID)  AS NumberofUpdates,
DATEDIFF (Question.LoggedTime,MIN(qUpdate.UpdateTime)) AS TimeBeforeFirstUpdate,
DATEDIFF(Question.LoggedTime, MAX(qUpdate.UpdateTime)) AS TimeBeforeLastUpdate
FROM qUpdate
LEFT JOIN Question ON qUpdate.qID=Question.ID
WHERE Question.Status = 'closed' AND qUpdate.Update NOT NULL
GROUP BY Question.Status, Question.ID, Question.LoggedTime;

If you need more info or any clarification I'll responsd ASAP.

回答1:

You don't need a "datediff" function.

Just subtract the two dates:

Question.LoggedTime - MIN(qUpdate.UpdateTime)

In case you don't know, but all that is documented online:
http://www.postgresql.org/docs/current/static/functions-datetime.html

回答2:

You can use the age(<date1>, <date2>) function (instead of DATEDIFF).

This should work -

SELECT Question.ID, 
Question.Status, COUNT (qUpdate.ID)  AS NumberofUpdates,
age(Question.LoggedTime,MIN(qUpdate.UpdateTime)) AS TimeBeforeFirstUpdate,
age(Question.LoggedTime, MAX(qUpdate.UpdateTime)) AS TimeBeforeLastUpdate
FROM qUpdate
LEFT JOIN Question ON qUpdate.qID=Question.ID
WHERE Question.Status = 'closed' AND qUpdate.Update NOT NULL
GROUP BY Question.Status, Question.ID, Question.LoggedTime;

Note, if psql gives you this error - ERROR: date/time field value out of range, then you would need to choose an appropriate datestyle.

回答3:

SELECT extract(year from age('2014-01-23', '1985-08-27'));
-- returns 28 years, my current age.

来源：https://stackoverflow.com/questions/10065894/calculating-difference-of-dates-in-postgresql

标签

sql

postgresql

datediff