PL / SQL-基本语法 - 芒果文档

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📜 PL / SQL-基本语法

📅 最后修改于: 2020-11-26 05:48:07 🧑 作者: Mango

在本章中，我们将讨论PL / SQL的基本语法，它是一种块结构语言。这意味着将PL / SQL程序划分并写入逻辑代码块中。每个块包含三个子部分-

S.No	Sections & Description
1	Declarations This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program.
2	Executable Commands This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable line of code, which may be just a NULL command to indicate that nothing should be executed.
3	Exception Handling This section starts with the keyword EXCEPTION. This optional section contains exception(s) that handle errors in the program.

S.No

Sections & Description

Declarations

This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program.

Executable Commands

This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable line of code, which may be just a NULL command to indicate that nothing should be executed.

Exception Handling

This section starts with the keyword EXCEPTION. This optional section contains exception(s) that handle errors in the program.

每个PL / SQL语句均以分号(;)结尾。可以使用BEGIN和END将PL / SQL块嵌套在其他PL / SQL块中。以下是PL / SQL块的基本结构-

DECLARE 
    
BEGIN 
   
EXCEPTION 
    
END;

“ Hello World”示例

DECLARE 
   message  varchar2(20):= 'Hello, World!'; 
BEGIN 
   dbms_output.put_line(message); 
END; 
/

结束;行表示PL / SQL块结束。要从SQL命令行运行代码，您可能需要在代码的最后一行之后的第一个空白行的开头键入/。当以上代码在SQL提示符下执行时，将产生以下结果-

Hello World  

PL/SQL procedure successfully completed.

PL / SQL标识符

PL / SQL标识符是常量，变量，异常，过程，游标和保留字。标识符由一个字母组成，可以选择在其后跟随更多字母，数字，美元符号，下划线和数字符号，并且不得超过30个字符。

默认情况下，标识符不区分大小写。因此，您可以使用整数或整数表示数字值。您不能使用保留关键字作为标识符。

PL / SQL分隔符

分隔符是具有特殊含义的符号。以下是PL / SQL中的分隔符列表-

Delimiter	Description
*+, -, , /**	Addition, subtraction/negation, multiplication, division
%	Attribute indicator
‘	Character string delimiter
.	Component selector
(,)	Expression or list delimiter
:	Host variable indicator
,	Item separator
“	Quoted identifier delimiter
=	Relational operator
@	Remote access indicator
;	Statement terminator
:=	Assignment operator
=>	Association operator
\|\|	Concatenation operator
**	Exponentiation operator
<<, >>	Label delimiter (begin and end)
*/, /*	Multi-line comment delimiter (begin and end)
—	Single-line comment indicator
..	Range operator
<, >, <=, >=	Relational operators
<>, ‘=, ~=, ^=	Different versions of NOT EQUAL

PL / SQL注释

程序注释是解释性语句，可以包含在您编写的PL / SQL代码中，可帮助任何人阅读其源代码。所有编程语言都允许某种形式的注释。

PL / SQL支持单行和多行注释。 PL / SQL编译器将忽略任何注释中可用的所有字符。 PL / SQL单行注释以定界符-(双连字符)开头，多行注释由/ *和* /括起来。

DECLARE 
   -- variable declaration 
   message  varchar2(20):= 'Hello, World!'; 
BEGIN 
   /* 
   *  PL/SQL executable statement(s) 
   */ 
   dbms_output.put_line(message); 
END; 
/

当以上代码在SQL提示符下执行时，将产生以下结果-

Hello World

PL/SQL procedure successfully completed.

PL / SQL程序单元

PL / SQL单元是以下任意一项-

PL / SQL块
功能
包
包装体
程序
触发
类型
型体

在以下各章中将讨论这些单元中的每个单元。