Generate SQL Query to segment survey data

We often need to analyse survey data for our client which is taken
from tools such as SurveyGizmo / SurveyMonkey and is sent to use
as CSV file.

I'd like to load this into MySQL and then run some queries against it
to identify certain patterns. The reason why I want to do it in MySQL
is that Excel grinds to a halt when you try and do something similar with
10,000's of rowas

I've attached a spreadsheet that contains a sample of the data

Calculate Percentages for Segments
If you take a look at Column C, you'll see the ages the people could
choose from in a survey. These come from a list and therefore
there can only be certain choices

What I'd like to be able to do is get % breakdown of each item i.e.

At a single column level (C)
15-18 - 36%
35-44 - 25%

with the sum adding up to 100%

Then at multiple column level where I want to get a better
demographic breakdown - in this case I'm cross matching columns C
and D, but I may want to cross match 3 or 4 columns to get a total

Men - 15-18 - 16%
Women - 15-18 - 20%

Calculate NetPromoter Score
The Netpromoter score is used to identify your most loyal customers
and you can see more here

http://www.satmetrix.com/net-promoter/net-promoter-score/calculating-your-net-promoter-score/

It asks people to rank how likely they are to recommend your
company on a scale of 1-10.

Promoters (score 9–10) are loyal enthusiasts who keep buying and
refer others, fueling growth.

Passives (score 7–8) are satisfied but unenthusiastic customers who
are vulnerable to competitors.

Detractors (score 0–6) are unhappy customers who can damage your
brand and impede growth through negative word of mouth.

Your Netpromter score is % of Promoters - the % of detractors

In the attached Excel sheet the overall net promoter score is 44%

61% (Promoters) - 17% (Detractors)

What I'd like to be able to do is calculate the Netpromoter score for
the whole database and then for particular segments (as above), so
it could by by age (Column C) or by Gender & Age (D & C)

Thus then allows me to see are there any particular demographics
that stand out

Outputs
We'll be running MySQL locally via Wampserver and using tool such
as HeidiSQL to run the queries

The SQL that you write will need to be easily modified so that we
adapt it for differnt survey questions