使用优先级字段获取已连接的mysql表上的最大值/最小值

Question

I have three tables to describe jobs that have tasks:

job:
jobId (int)
name (varchar)

task:
taskId (int)
jobId (int)
statusId (int)
name

taskStatus:
taskStatusId (int)
name (varchar)
priority (int)

I want to present the user with a list, that shows every jobs, and in the list, I need to show the name and status of the task with the highest and lowest priority. For example:

Job                 Highest priority task     Highest pri. task status
Build a house          Build the base              Very high

I am using MySQL and so far all I could come up was to use triggers to query and store the name and status of the highest and lowest tasks for every job in the jobs table, but I would like to solve this in the select query, if that's possible.

Any suggestions? Thanks

Answer 1

One way to approach this is with nested scalar subqueries:

select j.name,
       (select ts.name
        from task t join
             taststatus ts
             on t.name = ts.name
        where t.jobid = j.jobid
        order by priority
        limit 1
       ) as HighestPriority,
       (select ts.status
        from task t join
             taststatus ts
             on t.name = ts.name
        where t.jobid = j.jobid
        order by priority
        limit 1
       ) as HighestPriorityStatus
from job j;

This is likely to result in the best performance, if you have the appropriate indexes: task(jobid, name) , taskstatus(name, priority, status) .