将sql查询组合在一起

Question

I am trying to simplify my current query code. Is there a simpler way of combining both queries into one?

Here is what I have tried so far. Although it seems really messy and clunky. This query requests all the clients

SELECT * FROM clients ORDER BY name DESC

I then have another request inside to find if the client has a booking

SELECT * FROM bookings WHERE client_id=$client_id AND done=0

Done represents if the job is completed, and there can only be 1 uncompleted job per client at a time.

Explanation:

The code needs to show all the clients and if the client has a booking and if the other database returns a result, the booking button won't appear, if no results (ie, all previous bookings for that client are 1) a book button appears.

Answer 1

If you just want a flag, then you can use EXISTS :

SELECT c.*, 
       (EXISTS (SELECT 1
                FROM bookings b
                WHERE ON c.client_id = b.client_id AND b.done = 0
               )
       ) as has_booking
FROM clients c ;

Answer 2

I think you want:

select c.*, coalesce(b.done, 1) completed
from clients c
left join bookings b on b.client_id = c.client_id and b.done = 0

This attempts to find a uncompleted row in booking for each client. Column completed in the resultset contains 0 if the client has an uncompleted row, else 1 .

Answer 3

SELECT clients.*, bookings.done
FROM clients
LEFT JOIN bookings ON bookings.client_id = clients.client_id
AND b.done = 0

With the above result, you can add a condition in your view

if(done == 0){
     show button code
}