title: mysql setting a negative integer value to a primary auto increment field which is int
body: <p>I have a table which maintains categories from another site.</p>
  
  <p>I populate this table with the data i fetch from other site as xml.</p>
  
  <p>The data are divided as categories and products. </p>
  
  <p>Some products does not have a category and the category xml does not have the others category.</p>
  
  <p>So what i thought was to add a category others and setting its primary auto increment ID field to -1. So while inserting values into products table for all the entries which dosent have a category i am setting to -1.</p>
  
  <p>The auto increment initial values is 1.</p>
  
  <p>Is this a good practice. will it be valid or will it be a problem sometimes later for some conditions(any)?</p>
  
  <p>The db operations are working well but i want to know if it could be a problem later.</p>