title: Select n amount of random rows where n is proportionate to each value's % of total population
body: <p>I have a table of 58 million customer records. Each customer has a market value (EN, US, FR etc.)</p>
  
  <p>I'm trying to select a 100k sample set which contains customers from every market. The ratio of customers per market in the sample must match the ratios in the actual table.</p>
  
  <p>So if UK customers account for 15% of the records in the customer table then there must be 15k UK customers in the 100k sample set and the same then for each market.</p>
  
  <p>Is there a way to do this?</p>