这意味着其中一个字段您尚未指定表名存在于两个表中的位置。它可以是Total，Severity或QID。只要把T1。或T2。在每个字段的前面，即使在ORDER BY子句中也应该修复错误。

It means one of the fields where you haven't specified the table name exists in both tables. It could be Total, Severity, or QID. Just put T1. or T2. in front of each field, even in the ORDER BY clause and that should fix the error.