SQL - Row sum with condition from 2 tables

问题

I have 2 tables and want to get the row sum from 2 tables with conditions. Here are my tables:

tabale1, tabale2

i want the row sum from 2 tables, like:

if sk not null sum sk but if it is null sk = ss 

For example, the total sum of sh2 is: 19 + 5 + 11 + 5 = 40

I really need that, please help!

Table1:

Table2:

回答1:

Next sql will return the sum over the tables, grouping by name:

select name, sum(total) total from 
(select name, sum(coalesce(sk,ss)) total
 from table1
 group by name
 union all
 select name, sum(coalesce(sk,ss)) total
 from table2
 group by name
) t
group by name

The clause "group by" inside of the subqueries is very important because whether the tables return a lot of lines, they will reduce the number of lines for the "group by" on the query, optimizing time and using less memory.

回答2:

Use coalesce to pick sk if sk is not null. Otherwise (if sk is null), ss will be used.

UNION ALL the two tables, and GROUP BY its result:

select name, sum(skss)
from 
(
    select name, coalesce(sk, ss) skss
    from table1
    union all
    select name, coalesce(sk, ss) skss
    from table2
) dt
group by name

来源：https://stackoverflow.com/questions/43162761/sql-row-sum-with-condition-from-2-tables