配置大小写不敏感字符集引起的性能下降

SELECT os.id as telemarketId, oi.orderNo as orderNo, rr.backTime as backTime, IF(os.id is null,0,1) as flag
FROM test_info oi
LEFT JOIN rent_test rr on rr.rentRecordNo = oi.orderNo
LEFT JOIN test_snapshot os on oi.orderNo = os.orderNo
where rr.state > -6 and IFNULL(rr.backTime,‘0000-00-00 00:00:00’) != IFNULL(os.backTime,‘0000-00-00 00:00:00’)
limit 10;

where不等式的左边不能用函数
会走全表扫描