tailieunhanh - Writing Basic SQL SELECT Statements

SQL statements are not case sensitive. SQL statements can be on one or more lines. Keywords cannot be abbreviated or split across lines. Clauses are usually placed on separate lines. Indents are used to enhance readability. | Writing Basic SQL SELECT Statements Schedule: Timing Topic 40 minutes Lecture 25 minutes Practice 65 minutes Total Objectives After completing this lesson, you should be able to do the following: List the capabilities of SQL SELECT statements Execute a basic SELECT statement Differentiate between SQL statements and iSQL*Plus commands Lesson Aim To extract data from the database, you need to use the structured query language (SQL) SELECT statement. You may need to restrict the columns that are displayed. This lesson describes all the SQL statements needed to perform these actions. You may want to create SELECT statements that can be used more than once. This lesson also covers the iSQL*Plus environment where you execute SQL statements. Note: iSQL*Plus is new in the Oracle9i product. It is a browser environment where you execute SQL commands. In prior releases of Oracle, SQL*Plus was the default environment where you executed SQL commands. SQL*Plus is still available and is described . | Writing Basic SQL SELECT Statements Schedule: Timing Topic 40 minutes Lecture 25 minutes Practice 65 minutes Total Objectives After completing this lesson, you should be able to do the following: List the capabilities of SQL SELECT statements Execute a basic SELECT statement Differentiate between SQL statements and iSQL*Plus commands Lesson Aim To extract data from the database, you need to use the structured query language (SQL) SELECT statement. You may need to restrict the columns that are displayed. This lesson describes all the SQL statements needed to perform these actions. You may want to create SELECT statements that can be used more than once. This lesson also covers the iSQL*Plus environment where you execute SQL statements. Note: iSQL*Plus is new in the Oracle9i product. It is a browser environment where you execute SQL commands. In prior releases of Oracle, SQL*Plus was the default environment where you executed SQL commands. SQL*Plus is still available and is described in Appendix C. Capabilities of SQL SELECT Statements Selection Projection Table 1 Table 2 Table 1 Table 1 Join Capabilities of SQL SELECT Statements A SELECT statement retrieves information from the database. Using a SELECT statement, you can do the following: Projection: You can use the projection capability in SQL to choose the columns in a table that you want returned by your query. You can choose as few or as many columns of the table as you require. Selection: You can use the selection capability in SQL to choose the rows in a table that you want returned by a query. You can use various criteria to restrict the rows that you see. Joining: You can use the join capability in SQL to bring together data that is stored in different tables by creating a link between them. You learn more about joins in a later lesson. Instructor Note Inform students that selection and projection are often considered horizontal and vertical partitioning. Basic SELECT Statement SELECT *|{[DISTINCT] .