Help with JOIN and arithmetic

I've never used JOIN, and have tried getting some good examples on the
web, but am getting more confused.

I have two tables. In the first table, I have a date field (among
others) that represents the last date some event occurred. In the
second table, I have another date field that represents when this
particular record was created. Each time such an event occurs for the
appropriate record in the first table, a new record is created in the
second table with the date it occurred, and the date field in the first
table is updated with the same date. What I want to do is have an SQL
statement that queries both tables for a difference in dates over a
given period.

For example:

table1
id varchar(5)
lastFound date

table2
id varchar(5)
seq int(5) autoincrement
created date

And I want to find those records where "table1.lastFound -
table2.created > 60" AND "table2.seq = 1".

Thanks!

spride@gmail.com wrote:
> I've never used JOIN, and have tried getting some good examples on the
> web, but am getting more confused.

Joins are essential to using relational databases. It would be worth
your time to make sure you understand joins. You can google for "sql
join tutorial" or something like that.

Or you can look for a good book. Here are a few web pages with book
recommendations:

http://databases.about.com/cs/sql/tp/sqlbooks.htm
http://www.ocelot.ca/mysql.htm
http://theopensourcery.com/osbksql.htm

> I want to find those records where "table1.lastFound -
> table2.created > 60" AND "table2.seq = 1".

Here are a couple of queries that should give you those results.

SELECT ...
FROM table1 JOIN table2 USING (id)
WHERE TO_DAYS(table1.lastFound - table2.created) > 60
AND table2.seq = 1

SELECT ...
FROM table1 JOIN table2 USING (id)
WHERE table1.lastFound > table2.created + INTERVAL 60 DAY
AND table2.seq = 1

I'd prefer the latter, for performance reasons. If one has an index on
table1.lastFound, this query can benefit from the index, while the
former query can't.

Regards,
Bill K.