sql - Selecting data not matching query -

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i want select data not match query.

say have 2 tables:

cars: 

id         int          primary key identity make       varchar(255) not null model      varchar(255) not null pricegroup varchar(1)   not null

rentals:

id         int          primary key identity sdate      date         not null edate      date         not null car_id     int          not null

sdate in rentals starting date of rental - edate end date.

i want find available cars between specified time period.

this query works: 

select * cars id not in    (select car_id rentals sdate <='2013-04-28' , edate >='2013-04-30')

however, works specific dates. if enter period between 2013-04-25 , 2013-05-30 cars shows up, though of them booked in between period.

i use ms sql 2012.

you need compare dates other way around:

select * cars id not in    (select car_id rentals sdate <='2013-04-30' , edate >='2013-04-28')

also, using not exists may give better performance not in:

select * cars not exists   (select 1 rentals car_id=cars.id , edate>=start_date , sdate<=end_date)

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