title: how do I write an SQL INSERT query that will avoid duplicating data that are in a range on a row
body: <pre><code> id | user_id | job_range | start_date | client_name| job_type | job_no     |  job_quan                        
   1  |    4    | 1-3000    | 2014-05-13 |  kenny's   | coloured |   t50000   |    n4500
   2  |    2    | 3001-4500 | 2014-05-13 |  kenny's   | coloured |   t50000   |    n4500
   3  |    3    | 1-2000    | 2014-05-15 |  fredy's   | plain    |   t42100   |    n5000
   4  |    4    |2001-5000  | 2014-05-15 |  fredy's   | plain    |   t42100   |    n5000 
  </code></pre>
  
  <p>I want to write a query that uses range of numbers already inputted into the database (job_range) and matches it with a  job_no to avoid another user from putting jobs in the job range into the database.
  the number cannot be within the lower range already given. for any specific job, if there is a range of 1-2000 then you cannot add another row to the table for that job with the range starting between the 1-2000, only jobs from 2001 to 5000 can be picked. so user can only chose to do jobs btw range 2001 -5000</p>