考虑下图所示的关系数据库，主码加了下划线。给出关系代数表达式来表达下列的每一个查询：
a.找出First Bank Corporation的所有员工姓名
b.找出First Bank Corporation所有员工的姓名和居住城市
c.找出First Bank Corporation所有年收入在10000美元以上的员工姓名和居住的街道、城市。
d.找出所有居住地与工作的公司在同一城市的员工姓名
e.假设公司可以位于几个城市中。找出满足下面条件的所有公司，它位于Small Bank Corporation所位于的每一个城市。
a.
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\prod_{}{person\_name} (\sigma_{company\_name = “First Bank Corporation” }(works))
∏person_name(σcompany_name=“FirstBankCorporation”(works))
b.
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\prod_{}{person\_name,city }{ }(employee \Join(\sigma_{company\_name = “First Bank Corporation”} (works)))
∏person_name,city(employee⋈(σcompany_name=“FirstBankCorporation”(works)))
c.
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\prod_{}person\_name, street, city(\sigma_{(company\_name = “First Bank Corporation” ∧ salar y > 10000)}works \Join employee)
∏person_name,street,city(σ(company_name=“FirstBankCorporation”∧salary>10000)works⋈employee)
d.
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\prod_{}person\_name (employee \Join works \Join company)
∏person_name(employee⋈works⋈company)
e.
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\prod_{}company\_name (company ÷(\prod_{}city (\sigma_{company\_name =“Small Bank Corporation”} (company))))
∏company_name(company÷(∏city(σcompany_name=“SmallBankCorporation”(company))))
