大家对于礼宾员不是很陌生，在很多的酒店或者高档场所都有礼宾员，但是人们不知道礼宾员是做什么的，接下来给大家详细说一下。
http://en.wikipedia.org/wiki/Relational_algebra#Semijoin Let\'s say that I have two tables:A and B.I want to make a query that would work similarly to th开发者_高级运维e following SQL statement using
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