First query: All employees that has subscribed to Chess or Football but has no subscriptions of Tennis.
Second query: All empid's that has subscribed to Chess or football.
Your second query is filtering subscriptions and one subscription can only link to one facility. That means that if you have a subscription of Chess it will of course not at the same time be a subscription for Tennis and if you find a subscription of Tennis it will already be excluded be because it is not Chess or Football. Any EmpID that subscribes to both Chess and Tennis will be included because of the subscription of Chess but it will not be excluded because of the subscription of Tennis.
发布评论
评论（1）
第一个查询：
所有订阅了国际象棋或足球但没有订阅网球的员工。
第二个查询：
所有已订阅国际象棋或足球的 empid。
您的第二个查询是过滤订阅，一项订阅只能链接到一项设施。这意味着，如果您订阅了国际象棋，它当然不会同时订阅网球，如果您发现订阅了网球，那么它已经被排除在外，因为它不是国际象棋或足球。任何同时订阅 Chess 和 Tennis 的 EmpID 都将因为订阅 Chess 而被包含在内，但不会因为订阅 Tennis 而被排除。
First query:
All employees that has subscribed to Chess or Football but has no subscriptions of Tennis.
Second query:
All empid's that has subscribed to Chess or football.
Your second query is filtering subscriptions and one subscription can only link to one facility. That means that if you have a subscription of Chess it will of course not at the same time be a subscription for Tennis and if you find a subscription of Tennis it will already be excluded be because it is not Chess or Football. Any EmpID that subscribes to both Chess and Tennis will be included because of the subscription of Chess but it will not be excluded because of the subscription of Tennis.