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标题: 为什么需要Reflexive Join [打印本页]

作者: shiyiming 时间: 2011-1-9 14:49
标题: 为什么需要Reflexive Join
例题(来自adv prep guide)：
Suppose you want to list the names of supervisors for the crew on the flight to Copenhagen on March 4, 2000.

sasuser.flightschedule (empid, date, destination)
sasuser.staffmaster (empid, firstname, lastname, state)
sasuser.payrollmaster (empid, jobcode)
sasuser.supervisors（empid, state, jobcategory)

proc sql;
  select distinct e.firstname, e.lastname
from sasuser.flightschedule as a,
         sasuser.staffmaster as b,
         sasuser.payrollmaster  as c,
         sasuser.supervisors    as d,
         sasuser.staffmaster    as e
where a.date='04mar2000'd and
            a.destination='cph' and
            a.empid=b.empid and
            a.empid=c.empid and
            d.jobcategory=substr(c.jobcode,1,2)
            and d.state=b.state
            and d.empid=e.empid;
quit;

我的问题是：为什么list sasuser.staffmaster 两次，有必要吗？

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