Lesson01 学会使用基本的SQL语句

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 SQL*1-3 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Lesson Agenda • Basic SELECT statement • Arithmetic expressions and NULL values in the SELECT statement • Column aliases • Use of concatenation operator, literal character strings, alternative quote operator, and the DISTINCT keyword • DESCRIBE command1-4 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Basic SELECT Statement SELECT *|{[DISTINCT] column|expression [alias],...} FROM table; • SELECT identifies the columns to be displayed • FROM identifies the table containing those columns1-6 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Writing SQL 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. • In iSQL*Plus, SQL statements can optionally be SQL* terminated by a semicolon (;). Semicolons are required if you execute multiple SQL statements. • In SQL*plus, you are required to end each SQL SQL* statement with a semicolon (;).1-9 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Column Heading Defaults • iSQL*Plus: SQL* – Default heading alignment: Center – Default heading display: Uppercase • SQL*Plus: SQL* – Character and Date column headings are Left- aligned – Number column headings are right-aligned – Default heading display: Uppercase1-10 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Arithmetic Expressions Create expressions with number and date data by using arithmetic operators. Operator Description + Add - Subtract * Multiply / Divide1-11 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Operator Precedence SELECT last_name, salary, 12*salary+100 12* FROM employees; 1 … SELECT last_name, salary, 12*(salary+100) 12* FROM employees; 2 …1-13 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Defining a Null Value • A null is a value that is unavailable, unassigned, unknown, or inapplicable. • A null is not the same as a zero or a blank space. SELECT last_name, job_id, salary, commission_pct FROM employees; … …1-14 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Null Values in Arithmetic Expressions Arithmetic expressions containing a null value evaluate to null. SELECT last_name, 12*salary,12*salary*(1+commission_pct) 12* 12* salary* FROM employees; … …1-15 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Defining a Column Alias A column alias: • Renames a column heading • Is useful with calculations • Immediately follows the column name (There can also be the optional AS keyword between the column name and alias.) • Requires double quotation marks if it contains spaces or special characters or if it is case- sensitive • Can not be used in Where clause1-16 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Using Column Aliases SELECT last_name AS name, commission_pct comm FROM employees; … SELECT last_name "Name" , salary*12 "Annual Salary" salary* FROM employees; …1-17 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Concatenation Operator A concatenation operator: • Links columns or character strings to other columns • Is represented by two vertical bars (||) • Creates a resultant column that is a character expression SELECT last_name||job_id AS "Employees" FROM employees; …1-18 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Concatenation Operator SELECT last_name||s||salary FROM employees; SELECT last_name||chr(39)||s||salary FROM employees; SELECT ASCII() FROM dual; SELECT ASCII(?) FROM dual;1-19 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Literal Character Strings • A literal is a character, a number, or a date that is included in the SELECT statement. • Date and character literal values must be enclosed by single quotation marks. • Each character string is output once for each row returned.1-20 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Duplicate Rows The default display of queries is all rows, including duplicate rows. SELECT department_id FROM employees; 1 … SELECT DISTINCT department_id FROM employees; 2 …1-22 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

SQL and iSQL*Plus Interaction SQL* SQL statements Oracle server Internet browser iSQL*Plus SQL* Query results commands Formatted report Client1-23 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

SQL Statements Versus iSQL*Plus Commands SQL* SQL iSQL*Plus SQL* • A language • An environment • ANSI standard • Oracle-proprietary • Keyword cannot be • Keywords can be abbreviated abbreviated • Statements manipulate • Commands do not allow data and table definitions manipulation of values in in the database the database • Runs on a browser • Centrally loaded; does not have to be implemented on each machine SQL iSQL*Plus SQL* statements commands1-24 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Overview of iSQL*Plus SQL* After you log in to iSQL*Plus, you can: SQL* • Describe table structures • Enter, execute, and edit SQL statements • Save or append SQL statements to files • Execute or edit statements that are stored in saved script files1-25 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Summary In this lesson, you should have learned how to: • Write a SELECT statement that: – Returns all rows and columns from a table – Returns specified columns from a table – Uses column aliases to display more descriptive column headings • Use the iSQL*Plus environment to write, save, and SQL* execute SQL statements and iSQL*Plus SQL* commands SELECT *|{[DISTINCT] column|expression [alias],...} FROM table;1-38 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1: Overview This practice covers the following topics: • Selecting all data from different tables • Describing the structure of tables • Performing arithmetic calculations and specifying column names • Using iSQL*Plus SQL*1-39 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q1: A SELECT statement can be used to perform these three functions: 1. Choose rows from a table. 2. Choose columns from a table. 3. Bring together data that is stored in different tables by creating a link between them. Which set of keywords describes these capabilities? A. difference, projection, join B. selection, projection, join C. selection, intersection, join D. intersection, projection, join E. difference, projection, product1-40 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q2: Evaluate this SQL statement: SELECT e.EMPLOYEE_ID,e.LAST_NAME, e.DEPARTMENT_ID, d.DEPARTMENT_NAME FROM EMPLOYEES e, DEPARTMENTS d WHERE e.DEPARTMENT_ID = d.DEPARTMENT_ID; In the statement, which capabilities of a SELECT statement are performed? A. selection, projection, join B. difference, projection, join C. selection, intersection, join D. intersection, projection, join E. difference, projection, product1-41 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q3: Evaluate this SQL statement: SELECT ename, sal, 12 *sal+100 12* FROM emp; The SAL column stores the monthly salary of the employee. Which change must be made to the above syntax to calculate the annual compensation as "monthly salary plus a monthly bonus of $100, multiplied by 12"? A. No change is required to achieve the desired results. B. SELECT ename, sal, 12 *(sal+100) FROM emp; 12* C. SELECT ename, sal, (12 *sal)+100 FROM emp; (12* D. SELECT ename, sal+100, *12 FROM emp; sal+100,*1-42 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q4: Which SQL statement generates the alias Annual Salary for the calculated column SALARY *12? SALARY* A. SELECT ename, salary *12 Annual Salary salary* FROM employees; B. SELECT ename, salary *12 "Annual Salary" salary* FROM employees; C. SELECT ename, salary *12 AS Annual Salary salary* FROM employees; D. SELECT ename, salary *12 AS INITCAP("ANNUAL salary* SALARY") FROM employees1-43 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q5: The CUSTOMERS table has these columns: CUSTOMER_ID NUMBER(4) NOT NULL CUSTOMER_NAME VARCHAR2(100) NOT NULL CUSTOMER_ADDRESS VARCHAR2(150) CUSTOMER_PHONE VARCHAR2(20) You need to produce output that states "Dear Customer customer_name, ". The customer_name data values come from the CUSTOMER_NAME column in the CUSTOMERS table. Which statement produces this output?1-44 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 A. SELECT dear customer, customer_name, FROM customers; B. SELECT "Dear Customer", customer_name || , FROM customers; C. SELECT Dear Customer || customer_name , FROM customers; D. SELECT Dear Customer || customer_name || , FROM customers; E. SELECT "Dear Customer " || customer_name || "," FROM customers; F. SELECT Dear Customer || customer_name || , || FROM customers;1-45 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

Practice 1 Q6: Which two are attributes of iSQL *Plus? (Choose two.) iSQL* A. iSQL*Plus commands cannot be abbreviated. iSQL* B. iSQL*Plus commands are accessed from a browser. iSQL* C. iSQL*Plus commands are used to manipulate data in iSQL* tables. D. iSQL*Plus commands manipulate table definitions in iSQL* the database. E. iSQL*Plus is the Oracle proprietary interface for iSQL* executing SQL statements.1-46 Copyright © 2011, www.OracleOnLinux.cn . Part rights reserved.

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Lesson01 学会使用基本的SQL语句

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Lesson01 学会使用基本的SQL语句 — Presentation Transcript