1) i run the code in phpmyadmin: ALTER TABLE `usu_cache` MODIFY COLUMN `cache_date` DATETIME NOT NULL default '0001-01-01 00:00:00';
it returns error:

SQL query:

ALTER TABLE `usu_cache` MODIFY COLUMN `cache_date` DATETIME NOT NULL default '0001-01-01 00:00:00'

MySQL said: Documentation
#1146 - Table 'new.usu_cache' doesn't exist

i can not find table usu_cache in the database.
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2) i did not use prefix in configure.php.

what can i do now?