sql-内部联接没有重复的返回集？

Question

Creating a mock help desk ticketing service.

I have a ticket table which holds all tickets created by the customer. I have a works_on table which holds all tickets which managers have claimed and are working on.

In both tables I have a customerid to identify the owner of the ticket.

In the customer menu, they can check all of their tickets that they created, whether they are open, in the ticket table or being worked on in the works_on table.

My code below is giving me the same ticket from both tables. I only want to see the ticket once. How can I do that?

SELECT * FROM ticket
INNER JOIN works_on
ON ticket.custid = works_on.customerid

Answer 1

Good day,

try using Group By

SELECT * FROM ticket
       INNER JOIN works_on
       ON ticket.custid = works_on.customerid
       GROUP BY ticket.custid

you can also try using DISTINCT

The SELECT DISTINCT statement is used to return only distinct (different) values

Answer 2

SELECT * FROM ticket
INNER JOIN works_on
ON ticket.custid = works_on.customerid
GROUP BY ticket.custid

This will group the results where the customer ID are the same.

If not the modify the select into a SELECT DISTINCT

Answer 3

You're joining on the wrong columns. When you join on customerid , it finds all the tickets for a customer, and all the works_on rows for that customer, and creates a cross-product between them. You should be joining on the ticket ID, so you get each ticket with its corresponding works_on row.

SELECT *
FROM ticket AS t
INNER JOIN works_on AS w ON t.ticket_id = w.ticket_id
WHERE t.custid = :customer