Magento upgrade: help with this error message

Question

My upgrade won't conclude. Can you help me "translating" to a simpler sentence this error message?

Error message

Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (DATABASE-incremental.salesrule_coupon_usage, CONSTRAINT FK_SALESRULE_COUPON_CUSTOMER_CUSTOMER_ID_CUSTOMER_ENTITY FOREIGN KEY (customer_id) REFERENCES customer_entity (entity_id) O)";i:1;s:1228:"#0 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/Resource/Setup.php(390): Mage::exception('Mage_Core', 'Error in file: ...')

So far I understand that a child table ("salesrule_coupon_usage") has a constraint ("FK_SALESRULE_COUPON_CUSTOMER_CUSTOMER_ID_CUSTOMER_ENTITY") that makes Magento compare to the parent table ("customer_entity") where there are some values ("entity_id") that aren't on the child table ("customer_id").

I'm ok removing values and I'd like to know if I have to remove them from the parent table.

Complete error

a:5:{i:0;s:477:"Error in file: "/is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/SalesRule/sql/salesrule_setup/mysql4-upgrade-1.4.0.0.0-1.4.0.0.1.php" - SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`DATABASE-incremental`.`salesrule_coupon_usage`, CONSTRAINT `FK_SALESRULE_COUPON_CUSTOMER_CUSTOMER_ID_CUSTOMER_ENTITY` FOREIGN KEY (`customer_id`) REFERENCES `customer_entity` (`entity_id`) O)";i:1;s:1228:"#0 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/Resource/Setup.php(390): Mage::exception('Mage_Core', 'Error in file: ...')
#1 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/Resource/Setup.php(289): Mage_Core_Model_Resource_Setup->_modifyResourceDb('upgrade', '0.7.12', '1.4.0.0.6')
#2 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/Resource/Setup.php(233): Mage_Core_Model_Resource_Setup->_upgradeResourceDb('0.7.12', '1.4.0.0.6')
#3 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/Resource/Setup.php(161): Mage_Core_Model_Resource_Setup->applyUpdates()
#4 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/App.php(363): Mage_Core_Model_Resource_Setup::applyAllUpdates()
#5 /is/htdocs/wpSERVER/www/clonsite-incremental/app/code/core/Mage/Core/Model/App.php(295): Mage_Core_Model_App->_initModules()
#6 /is/htdocs/wpSERVER/www/clonsite-incremental/app/Mage.php(596): Mage_Core_Model_App->run(Array)
#7 /is/htdocs/wpSERVER/www/clonsite-incremental/index.php(80): Mage::run('', 'store')
#8 {main}";s:3:"url";s:27:"/clonsite-incremental/admin";s:11:"script_name";s:31:"/clonsite-incremental/index.php";s:4:"skin";s:7:"default";}

Thank you!

Answer 1

I finally restored the database and files, went to the admin area and removed the sales rules and the clients (they were faulty in some database tables that I messed up prior to that). I previously exported to CSV the clients which are important, but removed the sales rules as they can easily be reproduced later on. Then I cleared the cache, logged out, overwrote files with the newer version, and went to the admin. It worked, and the upgrade completed.