sql query to dulicate each row 12 times : I have a table which has columns site,year and sales . this table is unique on site+year eg <br/> 

    site  year   sales
    a     2012   50
    b     2013   100
    a     2006    35

Now what i wanted to do is make this table unique on site+year+month. thus each row gets duplicated 12 times,a month column is added which is labelled from 1-12 and the sales values get divided by 12 thus

    site   year  month  sales
    a      2012  1      50/12
    a      2012  2      50/12
    ...
    a      2012  12     50/12
    ...
    
    b      2013   1     100/12 
    ...
    a      2006   12       35/12

i am doing this on python currently and it works like a charm ,but i need to do this on SQL(ideally postgre SQL since i will be using this as a datasource for tableau) 

it would be very helpful,if someone can provide the explanations with the solution as well,since i am a novice at this 

