《数据库原理与应用第三章.ppt

Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 从职工关系中检索所有工资值 SELECT 工资 FROM 职工 结果是： 1220 1210 1250 1230 1250 SELECT DISTINCT工资 FROM 职工 结果是： 1220 1210 1250 1230 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 单表查询 用户在查询时可根据应用的需要改变列的显示顺序 例2查询全体学生的姓名、学号、所在系。 查询全部列-将所有的列名在SELECT后面列出或者用*表示列名 例3 SELECT * FROM Student; 查询经过计算的值 例4查询全体学生姓名及其出生年份 SELECT Sname,1996-Sage FROM Student; Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 单表查询 目标列表达式不仅可以是算术表达式，还可以是字符串常量、函数等。 例5查询全体学生的姓名、出生年份和所有系，要求用小写字母表示所有系名 SELECT Sname,’Year of Birth:’,1996-Sage,ISLOWER(Sdept) FROM Student; 输出结果： Sname ’Year of Birth:’ 1996-Sage ISLOWER(Sdept) ------- ---------------- ------------- ------------------ 李勇 Year of Birth: 1976 cs 刘晨 Year of Birth: 1977 is 王名 Year of Birth: 1978 ma 张立 Year of Birth: 1977 is Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. [例5.*] 使用列别名改变查询结果的列标题 SELECT Sname NAME，Year of Birth: ’ BIRTH， 2000-Sage BIRTHDAY，ISLOWER(Sdept) DEPARTMENT FROM Student； 输出结果： NAME BIRTH BIRTHDAY DEPARTMENT ------- ---------------- ------------- ------------------ 李勇 Year of Birth: 1976 cs 刘晨 Year of Birth: 1977 is 王名 Year of Birth: 1978 ma 张立 Year of Birth: 1977 is Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 二、选择表中的若干元组 消除取值重复的行 查询满足条件的元组 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011