Les03(编写可执行的语句).pdf

编写可执行的语句 Copyright © 2009, Oracle. All rights reserved. 目标 本课将学习: • 识别PL/SQL的各个词汇单元 • 在PL/SQL 使用内置的SQL functions • 描述隐式替换或处理显示替换 • 编写嵌套块 • 编写可读的、正确编排的代码 3 - 2 Copyright © 2009, Oracle. All rights reserved. PL/SQL块中词汇单元 词汇单元: • Are building blocks of any PL/SQL block • Are sequences of characters including letters, numerals, tabs, spaces, returns, and symbols • 分为以下几类: – Identifiers – Delimiters – Literals – Comments 3 - 3 Copyright © 2009, Oracle. All rights reserved. PL/SQL 块语法和指南 • Literals: – 字符串和日期类型被需要用单引号括起来. – 数字类型可以以简单值或科学型 name := Henderson; • Statements can continue over several lines. 3 - 4 Copyright © 2009, Oracle. All rights reserved. 注释代码 • Prefix single-line comments with two hyphens (--). • Place multiple-line comments between the symbols /* and */. Example DECLARE ... annual_sal NUMBER (9,2); BEGIN -- Begin the executable section /* Compute the annual salary based on the monthly salary input from the user */ annual_sal := monthly_sal * 12; END; -- This is the end of the block / 3 - 5 Copyright © 2009, Oracle. All rights reserved. SQL Functions in PL/SQL • Available in procedural statements: – Single-row number – Single-row character – Data type conversion – Date – Timestamp – GREATEST and LEAST – Miscellaneous functions • Not available in procedural statements: – DECODE – Group functions AVG, MIN, MAX, COUNT, SUM, STDDEV,