Left Join with effective dates

Question

I have two tables. One table contains events and another table contains effective dates for a bunch of users.

user_id | date_effective | rate
U1        2015-01-01       08.00
U2        2015-01-01       09.00
U1        2015-02-01       10.00
U2        2015-02-01       11.00
U1        2015-03-01       12.00

event_id | date_event
E1         2015-01-15
E2         2015-02-15
E3         2015-03-15

I am pulling a report for every event a specific user is attached to and the effective date for that event for that user. For U1, it would look like this.

event_id | date_event | rate
E1         2015-01-15   08.00
E2         2015-02-15   10.00
E3         2015-03-15   12.00

I am thinking that the effective dates are going to need to be sorted in ascending order so I can pick the first one on a Left Join, which is the default behavior. The problem I am having is that it won't allow me to order the effective dates when doing a Left Join like so:

SELECT event.event_id, event.event_date, effective.rate
FROM event
LEFT JOIN effective ON effective.user_id=U1
ORDER BY effective.date_effective ASC

The other way I tried was to use a comparison operator in the ON clause of the Left Join, but that did not work. Did not really expect it to.

Any suggestions would be deeply appreciated!

Edit Requirements: For any event date, it needs to look backwards and find the first effective date that is before the event date. If there is an event that happens today with an effective date yesterday and an effective date a month ago, the effective date from yesterday should be used.

Answer 1

Did i understand you correctly? You want the first date_effective by an given user_id ?

With sub-queries:

SELECT * 
    ,date_effecitve = (SELECT top 1 date_effective
                       FROM effective
                       WHERE user_id = 'U1'
                         AND date_effective <= DATE_event
                       ORDER BY date_effective DESC)

    ,rate = (SELECT top 1 rate
             FROM effective
             WHERE user_id = 'U1'
               AND date_effective <= DATE_event
             ORDER BY date_effective DESC)
FROM event

Result user_id = U1

event_id  date_event    date_effective    rate
E1        15.01.2015    01.01.2015        8
E2        15.02.2015    01.02.2015        10
E3        15.03.2015    01.03.2015        12

Result user_id = U2

event_id  date_event    date_effective    rate
E1        15.01.2015    01.01.2015        9
E2        15.02.2015    01.02.2015        11
E3        15.03.2015    01.02.2015        11

EDIT: Deleted my join-code, because it was noch 100% correct.