SQL从多个表中选择并按特定条件排序

Question

I have 2 tables, customer and tickets

I want to be able to select from the tickets table and order by:

tickets.priority then customer.category_priority then tickets.queue_time

I have this query:

SELECT t.*
from tickets t
  JOIN customer c ON t.company = c.sequence
WHERE t.status <> 'Completed' AND t.queue = 'Y'
ORDER BY field(t.priority, 'Critical', 'High', 'Medium', 'Low'), t.queue_time ASC

which works great for the tickets.priority and tickets.queue_time

but im not sure how to incorporate the customer.category_priority

so in the customer table, i have columns with names like:

priority_computers
priority_telephone
priority_software

all INT fields and have a value of 0, 1 or 2

the row in tickets has a category column which is either Computers , Telephone , or Software and thats what needs to link to the above.

so, if a customer row has priority_computers of 2 and the tickets row is category = 'Computers' that would be at the top of the list because the customer record has the priority of 2 and it would also incorporate the other ORDER BY conditions

Examples:

Customers:

• Company A priority_computers = 1
• Company B priority_computers = 2
• Company C priority_computers = 3

Example One:

• Ticket 1 Company A priority = Medium category = Computers queue_time = 2015-11-20 08:00
• Ticket 2 Company B priority = Medium category = Computers queue_time = 2015-11-20 10:00:00
• Ticket 3 Company C priority = Medium category = Computers queue_time = 2015-11-20 08:30:00

This should output in the following order:

• Ticket 3
• Ticket 2
• Ticket 1

Example 2:

• Ticket 1 Company B priority = High category = Computers
  queue_time = 2015-11-20 12:00
• Ticket 2 Company A priority = Medium category = Computers queue_time = 2015-11-20 07:00:00
• Ticket 3 Company C priority = Medium category = Computers queue_time = 2015-11-20 07:00:00

This should output in the following order:

• Ticket 1
• Ticket 3
• Ticket 2

Answer 1

If I understand this correctly, then your problem is that you have to match data with column names somehow.

• customer.priority_computers for ticket.category = 'Computers'
• customer.priority_telephone for ticket.category = 'Telephone'
• customer.priority_software for ticket.category = 'Software'

This shows a database design flaw. There should be a customer_priority table instead with each row holding a customer, a category and the associated value. Then you could simply join.

As is, you must check data content and decide for a column to use in your query:

SELECT t.*
from tickets t
  JOIN customer c ON t.company = c.sequence
WHERE t.status <> 'Completed' AND t.queue = 'Y'
ORDER BY field(t.priority, 'Critical', 'High', 'Medium', 'Low')
  , case t.category 
      when 'Computers' then c.priority_computers
      when 'Telephone' then c.priority_telephone
      when 'Software' then c.priority_software
    end
  , t.queue_time ASC

Update: Here is a query you'd write, if you had a customer_priority table. You see, your query doesn't need to know what categories exist and how to treat them any longer.

SELECT t.*
from tickets t
  JOIN customer c ON t.company = c.sequence
  JOIN customer_priority cp ON cp.customer_id = c.sequence
                            AND cp.category = t.category
WHERE t.status <> 'Completed' AND t.queue = 'Y'
ORDER BY field(t.priority, 'Critical', 'High', 'Medium', 'Low')
  , cp.priority_value
  , t.queue_time ASC

Moreover: As mentioned, it is strange to have a table customer , but in tickets it's not called a customer , but a company , and in the customer table itself it's not called a customer number or ID either, but a sequence . This makes the queries less readable. I suggest, you change the names, if possible, so they are consistent.

Also your query shouldn't have to know what 'Critical' and 'High' means. There should be a table for priorities where each priority has a name and a value, so the query could simply pick the value and work with it without having to know anything else about the priorities.