如何从两个或多个相同的mysql表求和？

Question

I've got a couple of identical tables. They look like this:

Table 1 
--------------------
Username      Points 
User 1            10 
User 2            15 
User 2            1 
User 1            3 

Table 2
---------------------
Username       Points 
User 1             10 
User 2             15 
User 2             5 
User 1             15 

I'm using SELECT username, SUM( points ) AS total_points to calculate the points for particular user. And it workds perfect. But i want to SUM the results from two or more tables. Is that possible?

Answer 1

Use a UNION ALL if you don't want to discard duplicates between the tables.

select username, sum(points) as total_points
from (
  select username, points
  from table_1
  union all
  select username, points
  from table_2
) t

If you use UNION instead, then rows with the same username and points will only be counted (summed) once

But it sounds like you actually should put that into a single table. You might want to read up on database normalization.