Add column if it does not exist?

[Oliver Ruebenacker]

     Hello,

  What's the easiest way to add a column to a table but only if it does not
exist? Thanks!

     Best, Oliver

-- 
Oliver Ruebenacker
Senior Software Engineer, Diabetes Portal
<http://www.type2diabetesgenetics.org/>, Broad Institute
<http://www.broadinstitute.org/>