How to add two/multiple values together in mysql? How to write a function f(x)?

Question

I'm wondering how to add several values together. For example, I have a table1:

#|a1|a2|a3
-|--|--|--
1|##|##|##
2|##|##|##
3|##|##|##

and a table2:

#|b1|b2|b3
-|--|--|--
1|##|##|##
2|##|##|##
3|##|##|##

I want to get:

y = sum(a1) + b1(3)  -- Sum of a1 and the third element of b1.

Also, How can I do more complex functions like:

y = (a1(2) * 3 + b2(2) * a3(2)) / avg(b1)

Please tell us how we may identify the third element of `b1` in `table2`. — Tim Biegeleisen, Mar 29 '16 at 01:23
@TimBiegeleisen So there's even issue with getting b1(3) ? :/ — Bing Gan, Mar 29 '16 at 01:50
You will need some way of referring to the "third" row. Is there some sort of identifier which can be used? — Tim Biegeleisen, Mar 29 '16 at 01:53
give more details of your table especially relation between table 1 and table 2 could help more to understand your needs.. — Hilarius L. Doren, May 03 '16 at 09:29

score 0 · Answer 1 · edited May 23 '17 at 12:16

You can use Group by to get sum(a1) of table1.

Then you will need to join table2 on some condition.

Also, you need to specify the ordering condition for b1(3).

Look at: MySQL row order for “SELECT * FROM table_name

insertion time ordering is not guaranteed in mysql. Once you specified the ordering, you can use top 3 row by 'Limit' keyword. Ref: How do you select every n-th row from mysql

How to add two/multiple values together in mysql? How to write a function f(x)?

1 Answers1