tailieunhanh - SQL VISUAL QUICKSTART GUIDE- P46

SQL VISUAL QUICKSTART GUIDE- P46:SQL (pronounced es-kyoo-el) is the standard programming language for creating, updating, and retrieving information that is stored in databases. With SQL, you can turn your ordinary questions (“Where do our customers live?”) into statements that your database system can understand (SELECT DISTINCT city, state FROM customers;) | Chapter 15 Assigning Ranks Assigning Ranks Ranking which allocates the numbers 1 2 3 . to sorted values is related to top-n queries and shares the problem of interpreting ties. The following queries calculate ranks for sales values in the table empsales from the preceding section. Listings to rank employees by sales. The first two queries shows the most commonly accepted ways to rank values. The other queries show variations on them. Figure shows the result of each ranking method a to e combined for brevity and ease of comparison. These queries rank highest to lowest to reverse the order change or to or in the WHERE comparisons. Listing Rank employees by sales method a . See Figure for the result. Listing SELECT SELECT COUNT sales FROM empsales e2 WHERE AS ranking FROM empsales el Listing Rank employees by sales method b . See Figure for the result. Listing SELECT SELECT COUNT sales FROM empsales e2 WHERE 1 AS ranking FROM empsales el Listing Rank employees by sales method c . See Figure for the result. Listing SELECT SELECT COUNT sales FROM empsales e2 WHERE AS ranking FROM empsales el Listing Rank employees by sales method d . See Figure for the result. Listing SELECT SELECT COUNT DISTINCT sales FROM empsales e2 WHERE AS ranking FROM empsales el 430 SQL Tricks Listing Rank employees by sales method e . See Figure for the result. Listing SELECT SELECT COUNT DISTINCT sales FROM empsales e2 WHERE AS ranking FROM empsales el emp_id sales a b c d e E09 900 1 1 0 1 0 E02 800 2 2 1 2 1 E10 700 4 3 2 3 2 E05 700 4 3 2 3 2 E01 600 5 5 4 4 3 E04 500 8 6 5 5 4 E03 500 8 6 5 5 4 E06 500 8 6 5 5 4 E08 400 9 9 8 6 5 E07 300 10 10 9 7 6 Figure Compilation of results of Listings to . DBMS These