John John - 5 months ago 15
SQL Question

MySQL - How to SELECT based on value of another SELECT

I have a table that looks something like this:

Name Year Value
A 2000 5
A 2001 3
A 2002 7
A 2003 1
B 2000 6
B 2001 1
B 2002 8
B 2003 2


The user can query based on a range of years, and it will return the sum of Value grouped by Name, as such (assume queried years are 2000 - 2001):

Name SUM(Value)
A 8
B 7


Now, I wanted to insert a calculated field that outputs the ratio of the sum of the values of each name for ALL years to the sum of all values. Basically the percentage of all values attributed to A and B, respectively, like:

Name SUM(Value) % Of Total
A 8 0.484 (16 / 33)
B 7 0.516 (17 / 33)


Note that even though the user queried only 2000-2001, I want the calculation to use the sum across all years. I've been searching and experimenting for hours and I cannot figure out how. I only know how to sum across the queried years like so:

SELECT `Name`, SUM(`Value`)/(SELECT SUM(`Value`) FROM `table1`) AS "% of Total"
FROM `table1`
WHERE `Year` BETWEEN 2000 AND 2001
GROUP BY `Name`;


Please help! I'm very much a novice, and don't understand SQL in much depth, so please clarify any advanced code. Thank you for your kindness.

Answer

You can calculate the total (and from that the desired percentage) by using a subquery in the FROM clause:

SELECT Name,
       SUM(Value) AS "SUM(VALUE)",
       SUM(Value) / totals.total AS "% of Total"
FROM   table1,
       (
           SELECT Name,
                  SUM(Value) AS total
           FROM   table1
           GROUP BY Name
       ) AS totals
WHERE  table1.Name = totals.Name
AND    Year BETWEEN 2000 AND 2001
GROUP BY Name;

Note that the subquery does not have the WHERE clause filtering the years.