PL/SQL学习（一）

PL/SQL Block consists of three sections:

• The Declaration section (optional).
• The Execution section (mandatory).
• The Exception Handling (or Error) section (optional).

These are the Advantages of PL/SQL

• Block Structures: PL SQL consists of blocks of code, which can be nested within each other. Each block forms a unit of a task or a logical module. PL/SQL Blocks can be stored in the database and reused.

•  Procedural Language Capability: PL SQL consists of procedural language constructs such as conditional statements (if else statements) and loops like (FOR loops).

•  Better Performance: PL SQL engine processes multiple SQL statements simultaneously as a single block, thereby reducing network traffic.

• Error Handling: PL/SQL handles errors or exceptions effectively during the execution of a PL/SQL program. Once an exception is caught, specific actions can be taken depending upon the type of the exception or it can be displayed to the user with a message.

变量

格式：

variable_name datatype [NOT NULL := value ]; 

例子：

dept varchar2(10) NOT NULL := “HR Dept”;

指定变量值的两种方式：

1)   variable_name:= value;

 2)

       SELECT column_name

       INTO variable_name  

       FROM table_name 

       [WHERE condition];

变量范围：

• Local variables -定义在嵌套块里，不能被外部块访问
• Global variables - 定义在外部块里，可以供自己使用，也可以被其里面的嵌套块使用。

constant_name CONSTANT datatype := VALUE; 

例子：

salary_increase CONSTANT number (3) := 10;