If we had these tables related. lets say that table1 has foreign key the column d of table2. And we had a joined table like:

SELECT a,b,c,table2.e
FROM table1
CROSS JOIN table2
where table1.b= table2.d;

How can new values be inserted?

I don’t think you can query and update the same table so I created rating2 table (has same data).

update rating
set ratingdate = (ratingdate+25)
where stars = select avg(rating2.stars)
from rating2

Any advice would be appreciated asap.
Table: Rating
rID mID stars ratingDate
201 101 2 2011-01-22
201 101 4 2011-01-27
202 106 4 Null
203 103 2 2011-01-20
203 108 4 2011-01-12
203 108 2 2011-01-30
204 101 3 2011-01-09
205 103 3 2011-01-27
205 104 2 2011-01-22
205 108 4 Null
206 107 3 2011-01-15
206 106 5 2011-01-19
207 107 5 2011-01-20
208 104 3 2011-01-02

My situation like this: I got sales reports from two channels. Both of them have same format: product_id, sales_volume, month

What I need to do is to import these csv files and combine them into a single report: product_id, channel1_sale, chanel2_sale, month.

There are lots of products. Channel 1 and channel 2 may have same and different products.

I finally use your solution of “Inserting new rows and updating existing rows” to solve it. Additionally I made another temp table with one additional field to judge if the data comes from channel 1 or 2.

At first I import to temp table, then I use your method to transfer data from temp data to final table, then I truncate the dump table.

It works like a charm!

Thank you Xaprb, your article really rocks even it was written years ago!