从具有多个相似行的表中选择不同的行

Question

I'm trying to list all cars that are available for rent between two specific dates, using a procedure. The table of which I am to select from, bookings, looks similar to this;

CarNumber    StartDate    EndDate
1            2018-01-03   2018-01-05
2            2018-01-09   2018-01-14
3            2018-01-03   2018-01-04
2            2018-01-29   2018-02-2
3            2018-01-12   2018-01-16

This is my current procedure;

CREATE PROCEDURE available_cars (Start_Date DATE, End_Date DATE)
READS SQL DATA
    BEGIN
        SELECT DISTINCT CarNumber FROM bookings
        WHERE NOT StartDate BETWEEN Start_Date AND End_Date
           OR NOT EndDate BETWEEN Start_Date AND End_Date;
    END;

This, to my knowledge, correctly checks if the car is rentable between, Start_Date and End_Date, the issue is that it cannot take into account several rows with the same CarNumber. For example, if I were to call the procedure with the dates 2018-01-10 to 2018-01-12 the output will display;

CarNumber
1
3
2

Obviously Car 3 and Car 2 is not available to be rented between these dates, but due to the table including several bookings on several rows it checks the second booking as well.

So how do I account for this?

Answer 1

If you don't store unique key in your database you can make compound query checking rented cars between selected dates and then making a DIFF between all available cars and currently rented.

SELECT DISTINCT CarNumber
FROM bookings
WHERE CarNumber NOT IN (
        SELECT CarNumber FROM bookings
        WHERE StartDate BETWEEN Start_Date AND End_Date
        OR EndDate BETWEEN Start_Date AND End_Date)
        OR (StartDate < Start_Date AND EndDate > End_Date;

You can easily create procedure from that code.