计算字段总数与另一个表列值

room      | beds available | ****table room****
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room1     | 4
room2     | 2 
room3     | 4

room      | occupant       | ****table occupant****
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room1     | arnold
room1     | berry
room2     | charles
room2     | daisy
room3     | eric
room3     | frank
room3     | greg
room      | beds available | ****table room****