sql - select repeat visitors given two time periods -


I would like to find the percentage of repeat visitors on my site. Currently I am selecting users for one month and dividing that month from next month. Is it the best way to write this question to calculate the returnees?

Generates the result that looks right, but thinks if there is a more elegant solution. 

  from the SELECT table (table 'user') in the form of the total table where the table. Event IN ('event1', 'event2', 'event3') and table WHERE table.event IN ('event1', 'event2', 'event3') and table ('in the month (October') in the form of the month ('October') / (SELECT COUNT (table.user) newTotal. ) Or table. Month ('november')) AS percent_ return   
 The table structure looks like this, you have only one month for the same user or many of the same time period Buy event.   order_number User Month Event Gross 1 Jack October Event 2 30 2 Jack November Event 3 20 3 Jack November Event 3 20 4 Jack N Mercury event 2 30 5 Sam November Event 2 30 6 Zone October Event 3 20 7 Zone October Non-Event 20 
 class = "post-text" itemprop = " text "> 
 You do not need two subqueries that you want. Just use conditional aggregation:  
  SELECT (SUM (s.manth IN (october)) / SUM ( WHERE s.event IN ('event1', 'event2', 'event3') and s.gross & gt; 0;   
 In addition, a single quote is not required around the numerical constant.

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