tailieunhanh - Restricting and Sorting Data

Character strings and date values are enclosed in single quotation marks. Character values are case sensitive, and date values are format sensitive. The default date format is DD-MON-RR. | Restricting and Sorting Data Schedule: Timing Topic 45 minutes Lecture 30 minutes Practice 75 minutes Total Objectives After completing this lesson, you should be able to do the following: Limit the rows retrieved by a query Sort the rows retrieved by a query Lesson Aim While retrieving data from the database, you may need to restrict the rows of data that are displayed or specify the order in which the rows are displayed. This lesson explains the SQL statements that you use to perform these actions. Limiting Rows Using a Selection “retrieve all employees in department 90” EMPLOYEES Limiting Rows Using a Selection In the example on the slide, assume that you want to display all the employees in department 90. The rows with a value of 90 in the DEPARTMENT_ID column are the only ones returned. This method of restriction is the basis of the WHERE clause in SQL. Limiting the Rows Selected Restrict the rows returned by using the WHERE clause. The WHERE clause follows the FROM clause. . | Restricting and Sorting Data Schedule: Timing Topic 45 minutes Lecture 30 minutes Practice 75 minutes Total Objectives After completing this lesson, you should be able to do the following: Limit the rows retrieved by a query Sort the rows retrieved by a query Lesson Aim While retrieving data from the database, you may need to restrict the rows of data that are displayed or specify the order in which the rows are displayed. This lesson explains the SQL statements that you use to perform these actions. Limiting Rows Using a Selection “retrieve all employees in department 90” EMPLOYEES Limiting Rows Using a Selection In the example on the slide, assume that you want to display all the employees in department 90. The rows with a value of 90 in the DEPARTMENT_ID column are the only ones returned. This method of restriction is the basis of the WHERE clause in SQL. Limiting the Rows Selected Restrict the rows returned by using the WHERE clause. The WHERE clause follows the FROM clause. SELECT *|{[DISTINCT] column|expression [alias],.} FROM table [WHERE condition(s)]; Limiting the Rows Selected You can restrict the rows returned from the query by using the WHERE clause. A WHERE clause contains a condition that must be met, and it directly follows the FROM clause. If the condition is true, the row meeting the condition is returned. In the syntax: WHERE restricts the query to rows that meet a condition condition is composed of column names, expressions, constants, and a comparison operator The WHERE clause can compare values in columns, literal values, arithmetic expressions, or functions. It consists of three elements: Column name Comparison condition Column name, constant, or list of values Using the WHERE Clause SELECT employee_id, last_name, job_id, department_id FROM employees WHERE department_id = 90 ; Using the WHERE Clause In the example, the SELECT statement retrieves the name, job ID, and department number of all employees whose job ID is SA_REP. Note that the