Mysql select with IF函数子查询

Question

我正在尝试使用 php 进行查询。基本上，它应该首先检查是否没有进行特定预订，然后查询所有可用车辆和司机的数据库。

这是目前的查询:

IF EXISTS(SELECT * FROM bookings LEFT JOIN status WHERE bookings.status_id = '.$booking.')
            BEGIN
                select * 
                FROM bookings      as b 
                LEFT JOIN drivers  as d where b.driver_id !="d.driver_id"
                LEFT JOIN vehicles as v where b.vehicle_id !="v.vehicle_id"
                LEFT JOIN status   as s where b.status_id !="'.$booking.'"
                ORDER BY b.bookingDate DESC
            END

Answer 1

加入预订:

SELECT * 
FROM bookings      as b 
LEFT JOIN drivers  as d where b.driver_id !="d.driver_id"
LEFT JOIN vehicles as v where b.vehicle_id !="v.vehicle_id"
LEFT JOIN status   as s where b.status_id !="'.$booking.'"
CROSS JOIN (
    SELECT 1 
    FROM bookings 
    WHERE bookings.status_id = '.$booking.'
    LIMIT 1
) t
ORDER BY b.bookingDate DESC