PL/SQL中的=>作用

=> 是 Oracle 中调用 存储过程的时候,  指定 参数名进行调用.一般是， 某些参数有默认值的时候，你需要跳过某些参数来进行调用。下面是具体的例子。
参数的默认值
SQL> CREATE OR REPLACE PROCEDURE HelloWorld3 (

p_user_name VARCHAR2,

p_val1 VARCHAR2 DEFAULT ' Good Moning,',

p_val2 VARCHAR2 DEFAULT ' Nice to Meet you') AS

BEGIN
dbms_output.put_line('Hello ' || p_user_name || p_val1 || p_val2 || '!');
END HelloWorld3;

/
Procedure created.
SQL> BEGIN
HelloWorld3('Edward');
HelloWorld3('Edward', ' Good Night,');
HelloWorld3('Edward', ' Good Night,', 'Bye');
END;
/
Hello Edward Good Moning, Nice to Meet you!
Hello Edward Good Night, Nice to Meet you!
Hello Edward Good Night,Bye!
PL/SQL procedure successfully completed.

指定参数名称调用
此部分使用 “参数默认值”那一小节的存储过程。
用于说明当最后2个参数是有默认的时候，如何跳过中间那个。
SQL> BEGIN
HelloWorld3('Edward');
HelloWorld3('Edward', p_val1 => ' Good Night,');
HelloWorld3('Edward', p_val1 => ' Good Night,', p_val2 => 'Bye');
HelloWorld3('Edward', p_val2 => ' HeiHei ');
END;
/
Hello Edward Good Moning, Nice to Meet you!
Hello Edward Good Night, Nice to Meet you!
Hello Edward Good Night,Bye!
Hello Edward Good Moning, HeiHei !
PL/SQL procedure successfully completed.