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saltedfish
saltedfish
Last Activity: Sep 9 '10, 06:30 AM
Joined: Sep 8 '10
Location: WuHan, China
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  • saltedfish
    replied to How to convert sql to relational algebra?
    in SQL Server
    First thank you very much for you reply.
    I have unload a picture about the relational algebra.
    In fact, there are three tables: student, sc, course.
    course has cno and cname, respectively representing the number and name of course. sc has sno, cno, grade, respectlively representing number of student, number of course and the score.
    What I mean is this:
    Code:
    select sname 
      from student 
      where
    ...
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    • saltedfish
      started a topic How to convert sql to relational algebra?
      in SQL Server

      How to convert sql to relational algebra?

      Now I have a sql needed to be converted to relational algebra. There are two tables: student and sc.
      student has sno, sname, sage.
      sc has sno, cno, grade.
      How to translate the sql into relational algebra:
      select sname from student where sage > 20 or sno in (select sno from sc where grade > 90);

      I know it can be converted to union opertaion, but that is too complicated for many sqls like this....
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