有人请解释一下
ρ emp2.surname,emp2.forenames (
σ employee.empno = 3 ^ employee.depno = emp2.depno (
employee × (ρemp2employee)
)
)
有人请解释一下
ρ emp2.surname,emp2.forenames (
σ employee.empno = 3 ^ employee.depno = emp2.depno (
employee × (ρemp2employee)
)
)