Magento – How Many Tables Does Magento 2 Have

Start by creating a plain Magento 1.7 installation. Then run (separately):

select * from information_schema.statistics where TABLE_SCHEMA='YOUR_MAGENTO_DB';
select * from information_schema.statistics where TABLE_SCHEMA='PLAIN_MAGENTO_DB';

Each query will list the indexes in each database. You can then create a script to drop missing indexes/add new

There are multiple ways to save data to two tables at a time.

If you've registered the resource (table-backed) model in Magento's ORM you should be able to do something to the effect of:

$table1 = Mage::getModel('yourmodel/table1');
$table1->setData(array('some'=>'stuff','in'=>'here'));
$table1->save();

Wash, rinse, repeat for the second table - assuming you have a column called parent_id:

$table2 = Mage::getModel('yourmodel/table2');
$table2->setParentId($table1->getId());
$table2->setData($table1->getData());
$table2->save();

This accomplishes your goal of having a table2 related to table1 by the primary key.

Another thought is that if your RDBMS (MySQL?) has the concept of a trigger, you could set up a trigger.