SQL find percentage of group?

Question

I have an SQL table with a column of names and a column of prices they paid for tickets. What query can I use to find the percentage of people who paid more than £100? Thanks

Answer 1

You can use avg() to get the ratio:

select avg(case when price > 100 then 1.0 else 0 end)
from t;

Answer 2

select 
   100.0                                      -- to get a percentage
   * count(case when price > 100 then 1 end)  -- who paid over 100?
   / count(*)                                 -- all rows
from tickets