Lecture7Slides501.ppt - CSC 355 Database Systems Lecture 7...

Info icon This preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
CSC 355 Database Systems Lecture 7 Eric J. Schwabe School of Computing, DePaul University Winter 2018
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Today: SQL queries Joins 2
Image of page 2
Joins Data that is distributed among multiple tables can be combined into a single set of tuples for use in a query using different types of joins : Inner joins (equi-join, natural join) Outer joins (left, right, full) 3
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Cartesian Product What if we list two tables in the FROM? The tuples in the result come from combining all pairs of tuples from the two tables – the Cartesian Product of the tables (This is sometimes called the “cross join”…) This is almost certainly more tuples than we want – most combinations are meaningless! 4
Image of page 4
Equi-Joins An equi-join keeps only those tuples where the two combined tuples agree on the shared attribute(s): …FROM TABLE1, TABLE2 WHERE TABLE1.Attribute = TABLE2.Attribute ; 5
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Natural Joins Like an equi-join, but one of the duplicated columns is removed (the most common join): SELECT all but the duplicated attribute(s) FROM TABLE1, TABLE2 WHERE TABLE1.Attribute = TABLE2.Attribute ; 6
Image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern