I have 2 workers’ threads, one for install and one for delete. and one jobs table sqlite3. I want to select the next job to install but only if there is no job for the system to delete because the delete job needs to run first. For simplicity here is my table:

• System version operation
• windows 10 install
• windows 7 remove
• ubuntu 14 install

In this case, I want to select Ubuntu/14 install job, not windows 10 install job.