If you have recently upgraded your Magento website and tried to reindex your data, then you might be stuck at PRODUCT FLAT DATA reindexing. This problem is mainly due to the fact of too many attributes usage, etc.
In order to fix this,
- Edit
app/code/core/Mage/Catalog/Model/Resource/Product/Flat/Indexer.php
comment out this line :
//$adapter-quoteInto(’additional_table.is_used_for_promo_rules = ?’, 1),
inside function getAttributeCodes()
Article source: http://www.learnmagento.org/magento-tutorials/magento-reindexing-problem-with-product-flat-data/