Calculate percentage of String values in table

Question

I have a table, where questions have been answered either pass or fail.

I just need an SQL query to find the percentage of Fails for question 1 out of the total number of questions asked.

I'm trying this, but this is coming up with a Syntax error -

$CA001 = "COUNT(CA001Result WHERE CA001Result = "Fail") / COUNT(CA001Result)) From Datable";

As I said, total noob, it's MYSQL btw.

I no need to isolate the % results for Product, I've got this so far, and have tried GROUP by Product but that didn't work, any ideas?

$CA001 = "( SELECT ROUND(100 *  (SELECT count(CA001Result ) from Data_Table where (CA001Result='Fail' AND Product='$product' AND Area='$Area'))/count(CA001Result),2) from Data_Table) AS 'CA001 %'";

Looking at it again I need to insert a WHERE Product = 'Product' somewhere like where I have it below, however don't quite understand where to put it as the below doesn't work:

$ CA001 = "( SELECT ROUND(100 * (SELECT count(CA001Result ) from Data_Table where (CA001Result='Fail' AND Product='$product' AND Area='$Area'))/count(CA001Result WHERE Product = '$product'),2) from Data_Table) AS 'CA001 %'";

Answer 1

Suppose this is your table:

ID     Answer
-------------
 1  ,  'pass'
 2  ,  'pass'
 3  ,  'fail'
 4  ,  'fail'
 5  ,  'fail'
 6 ,   'fail'

So you need to use a subquery like this:

SELECT 100 * 
(SELECT COUNT(answer) FROM t WHERE answer='fail')/COUNT(answer)
AS Fail_percent FROM t;

Or you can use COUNT with CASE like this:

SELECT 100 * 
COUNT(CASE WHEN answer = 'fail' THEN 1 ELSE NULL END)/COUNT(answer)
AS Fail_percent FROM t;

Or you can use SUM with CASE like this:

SELECT 100 * 
SUM(CASE WHEN answer = 'fail' THEN 1 ELSE 0 END)/COUNT(answer)
AS Fail_percent FROM t;

Or you can use SUM without using CASE (Only for MySQL) like this:

SELECT 100 * 
SUM(answer = 'fail')/COUNT(answer)
AS Fail_percent FROM t;

See this SQLFiddle