Re: problem for selecting range of date between 2 dates

[Rick James]

CONCAT won't work because you don't have leading zeros on the month:
Last September would come after October: "20119" > "201110"

CONCAT(year, RIGHT(CONCAT('0', month), 2))
is a clumsy workaround for the leading zero issue.

12+year+month world work universally. (Ditto for 100*year+month.)

> ( year >= @start_year and mon >= @start_mon OR year > @start_year )
is incorrect. The AND will happen before the OR, so you need:
( year >= @start_year and ( mon >= @start_mon OR year > @start_year ) )
That is even reasonably efficient if you have
INDEX(year, com)

This should also work:
WHERE (year, month) >= (2011, 10) AND (year, month) <= (2012, 2)

None of the above scales well. (Indexes will not be used, or not used very well.)

Recommend you
1. ALTER TABLE ADD another column to contain the combined year_month.
2. UPDATE to set that new column
3. ALTER TABLE foo DROP COLUMN year, DROP COLUMN month;
The life will be much simpler!