Question

How can we get the sum of column entries in the NO-SQL database Redis?

I mean similar as :

    Select sum(salary) from Account;

Answer 1

The short answer is, you can’t. That’s not quite what redis was meant for.
The somewhat longer answer is, you can accomplish this with redis lua scripting, and the EVAL command.

With a redis list such as:

LPUSH mylist 1 2 3 4 5 6 7

And a script sum.lua:

local list = redis.call('lrange', KEYS[1], 0, -1)
local sum = 0
for i, val in ipairs(list) do
  sum = sum + val
end

return sum

You could call it from the command line, like this:

$ redis-cli EVAL "$(cat sum.lua)" 1 mylist
(integer) 28

Edit: The third answer is @DidierSpezia’s comment, about calculating it when permuting the data. Usually when working with redis, you will structure your data according to how you want to query it, rather than the other way around. Perhaps you would do something like:

# Paying out salary
redis> LPUSH employee:17:salaries 10000
redis> HINCRBY total_salaries 17 10000

# Fetching total salary to employee 17

redis> HGET total_salaries 17
"10000"