Is it possible to use values from another table as the interval in a DATEADD function?

问题

I have a table of events containing a date (smalldatetime). I have a table of intervals (int) (days before) for when a reminder should be sent - DATEADD(D, *interval*, GETDATE()).

I'm trying to write an SQL statement to get all the events where a reminder should be sent today (based on GETDATE() from the DATEADD function. This is instead of me first getting all the intervals and running SQL in a loop, passing each interval as a parameter into the DATEADD function.

Any ideas how I'd do this?

**dbo.events**
id (int) PK
date (smalldatetime)
customerID (int)

**dbo.intervals**
id (int) PK
daysBefore (int)
customerID (int)

回答1:

The answer is yes. I can't draw this query for you due to lack of information provided. But yes, you can.

Take this example:

MyTable:
ID    Interval    Date
1     1           10-10-2001

SELECT ID, DATEADD(D, Interval, GETDATE()) AS NewDate FROM MyTable


SELECT e.*
FROM [events] e
INNER JOIN [interval] i on e.customerID = i.customerID
WHERE e.date = DATEADD(D, i.daysBefore, 
                   DATEADD(D, 0, 
                       DATEDIFF(D, 0, GETDATE())))

回答2:

Yes. You should have tried it yourself

create table t(val int);
insert into t values(4),(7),(10)

select DATEADD(D, val, GETDATE()) from t

SQLFiddle

回答3:

Thanks everyone for showing how that's possible. I presume this would be how to write the SQL, unless there is a more efficient way?

SELECT *
FROM events
WHERE date IN (
    SELECT DATEADD(D,daysBefore,DATEADD(D, 0, DATEDIFF(D, 0, GETDATE())))
    FROM interval
    WHERE events.customerID = customerID);

SQLFiddle

来源：https://stackoverflow.com/questions/13001876/is-it-possible-to-use-values-from-another-table-as-the-interval-in-a-dateadd-fun

标签

sql

sql-server

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dateadd