【正文】
? Use table prefixes to qualify column names that are in multiple tables. ? Improve performance by using table prefixes. ? Distinguish columns that have identical names but reside in different tables by using column aliases. 411 SELECT , , , , FROM employees e , departments d WHERE = 。Displaying Data from Multiple Tables 42 Objectives After pleting this lesson, you should be able to do the following: ? Write SELECT statements to access data from more than one table using equality and nonequality joins ? View data that generally does not meet a join condition by using outer joins ? Join a table to itself by using a self join 43 Obtaining Data from Multiple Tables EMPLOYEES