Quick one!
# Warnings
cat /var/log/mysqld.log |grep `date +%y%m%d` | grep "\[Warning\]"
# Errors
cat /var/log/mysqld.log |grep `date +%y%m%d` | grep "\[ERROR\]"
And a Bonus!
To get entries from X days ago:
cat /var/log/mysqld.log |grep `date --date="46 days ago" +%y%m%d`
Matheus.