PL/SQL --> 流程控制

--=======================
--  PL/SQL --> 流程控制
--=======================
 
    类似于高级语言，流程控制语句是PL/SQL语言的重要组成部分。这些流程控制语句使得PL/SQL加大了代码的灵活性和多样性，大大简化了
程序的编写。下面将列出流程控制语句并给出具体事例。
   
一、顺序结构
    按代码的书写顺序依次执行
    --在下面的示例中将逐步执行代码
        scott@ORCL> declare v_ename varchar2(20);
          2  v_job emp.job%type;
          3  v_no  emp.empno%type;
          4  begin
          5    v_no:=&inputno;
          6    select ename,job into v_ename,v_job from emp where empno=v_no;
          7    dbms_output.put_line('Employee Name: '||v_ename);
          8    dbms_output.put_line('Employee Job : '||v_job);
          9  end;
         10  /
        Enter value for inputno: 7788
        old   5:   v_no:=&inputno;
        new   5:   v_no:=7788;
        Employee Name: SCOTT
        Employee Job : ANALYST
 
        PL/SQL procedure successfully completed.   
二、条件分支结构
    1.IF ... THEN ... END IF
        IF condition THEN
            statement
        END IF;
 
        判断condition是否成立，成立就执行IF 与END IF 之间的语句。
   
        --例：输入员工编号，查询其工资，如果他们的职位是CLERK，则工资增加%，再显示修改前后的工资数。
 
            DECLARE
                v_empid emp.empno%TYPE;
                v_job emp.job%TYPE;
                v_old_sal emp.sal%TYPE;
                v_new_sal emp.sal%TYPE;
            BEGIN
                v_empid:=&inputid;
                SELECT job,sal INTO v_job,v_old_sal FROM emp WHERE empno=v_empid;
                IF v_job='CLERK' THEN
                    v_new_sal:=v_old_sal*1.1;
                    UPDATE emp SET sal=v_new_sal WHERE empno=v_empid;
                    DBMS_OUTPUT.PUT_LINE('Old sal:'||v_old_sal);
                    DBMS_OUTPUT.PUT_LINE('New sal:'||v_new_sal);
                END IF;
            EXCEPTION
                WHEN NO_DATA_FOUND THEN
                    DBMS_OUTPUT.PUT_LINE('Not FOUND RECORD');
            END;
            /
 
    2.IF ... THEN ... ELSE ... END IF
        IF condition THEN
            statements1;
        ELSE
            statements2;
        END IF;
 
        判断condition是否成立，成立就执行IF 与ELSE 之间的语句，
        否则执行ELSE 与END IF之间的语句。
 
        --例：输入员工编号,查询其工资,如果他们的职位是CLERK,则工资增加%,如果不是CLERK,工资增加8%,再显示修改前后的工资数。
 
            DECLARE
                v_empid emp.empno%TYPE;
                v_job emp.job%TYPE;
                v_old_sal emp.sal%TYPE;
                v_new_sal emp.sal%TYPE;
            BEGIN
                v_empid:=&inputid;
                SELECT job,sal INTO v_job,v_old_sal FROM emp WHERE empno=v_empid;
                IF v_job='CLERK' THEN
                    v_new_sal:=v_old_sal*1.1;
                ELSE
                    v_new_sal:=v_old_sal*1.08;
                END IF;
 
                UPDATE emp SET sal=v_new_sal WHERE empno=v_empid;
                DBMS_OUTPUT.PUT_LINE('Old sal:'||v_old_sal);
                DBMS_OUTPUT.PUT_LINE('New sal:'||v_new_sal);
 
            EXCEPTION
                WHEN NO_DATA_FOUND THEN
                    DBMS_OUTPUT.PUT_LINE('Not FOUND RECORD');
            END;
            /
 
    3.IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF
        IF condition1 THEN
            statements1;
        ELSIF condition2 THEN
            statements2;
        ELSE
            else_statements;
        END IF;
 
        --例:输入员工编号,查询其工资,如果其职位是CLERK,则工资增加%,如果是SALESMAN工资增加%,其它的加%,显示修改前后的工资数。
 
            DECLARE
                v_empid emp.empno%TYPE;
                v_job emp.job%TYPE;
                v_old_sal emp.sal%TYPE;
                v_new_sal emp.sal%TYPE;
            BEGIN
                v_empid:=&inputid;
                SELECT job,sal INTO v_job,v_old_sal FROM emp WHERE empno=v_empid;
                IF v_job='CLERK' THEN
                    v_new_sal:=v_old_sal*1.1;
                ELSIF v_job='SALESMAN' THEN
                    v_new_sal:=v_old_sal*1.08;
                ELSE
                    v_new_sal:=v_old_sal*1.05;
                END IF;
 
                UPDATE emp SET sal=v_new_sal WHERE empno=v_empid;
                DBMS_OUTPUT.PUT_LINE('Old sal:'||v_old_sal);
                DBMS_OUTPUT.PUT_LINE('New sal:'||v_new_sal);
 
            EXCEPTION
                WHEN NO_DATA_FOUND THEN
                    DBMS_OUTPUT.PUT_LINE('Not FOUND RECORD');
            END;
            /
       
    4.等值比较的CASE多分支
       
        CASE expression
            WHEN result_1 THEN
            statements1;
            WHEN result_2 THEN
            statemnts2;
              ......
            [ELSE
            else_statements;]
        END CASE;
       
        --使用case分支完成前面的示例
        --例:输入员工编号,查询其工资,如果其职位是CLERK,则工资增加%,如果是SALESMAN工资增加%,其它的加%,显示修改前后的工资数。
            DECLARE
                v_empid emp.empno%TYPE;
                v_job emp.job%TYPE;
                v_old_sal emp.sal%TYPE;
                v_new_sal emp.sal%TYPE;
            BEGIN
                v_empid:=&inputid;
                SELECT job,sal INTO v_job,v_old_sal FROM emp WHERE empno=v_empid;
                CASE v_job
                    WHEN 'CLERK' THEN
                    v_new_sal:=v_old_sal*1.1;
                    WHEN 'SALESMAN' THEN
                    v_new_sal:=v_old_sal*1.08;
                    ELSE
                    v_new_sal:=v_old_sal*1.05;
                END CASE;
 
                UPDATE emp SET sal=v_new_sal WHERE empno=v_empid;
                DBMS_OUTPUT.PUT_LINE('Old sal:'||v_old_sal);
                DBMS_OUTPUT.PUT_LINE('New sal:'||v_new_sal);
 
            EXCEPTION
                WHEN NO_DATA_FOUND THEN
                    DBMS_OUTPUT.PUT_LINE('Not FOUND RECORD');
            END;
            /
 
    5.条件比较的CASE语句
        CASE
            WHEN expression_1 THEN
                statements1;
            WHEN expression_2 THEN
                statements2;
            WHEN expression_3 THEN
                statements3;
                ......
            [ELSE
                else_statements；]
        END CASE
       
        --使用case分支完成前面的示例，仅仅列出case 部分
            CASE
                WHEN v_job='CLERK' THEN
                v_new_sal:=v_old_sal*1.1;
                WHEN v_job='SALESMAN' THEN
                v_new_sal:=v_old_sal*1.08;
                ELSE
                v_new_sal:=v_old_sal*1.05;
            END CASE;
 
三、循环结构
    1.LOOP 循环
       
        LOOP
            statement;
            EXIT [WHEN condition];
        END LOOP;
 
        --例：用LOOP写一个程序求1＋＋＋＋. . . +10 之和
 
            DECLARE
                v_n INT:=1;
                v_s INT:=0;
            BEGIN
                LOOP
                    v_s:=v_s+v_n;
                    v_n:=v_n+1;
                    EXIT WHEN v_n>10;
                END LOOP;  
                DBMS_OUTPUT.PUT_LINE('1+2+3+...+10='||v_s);
            END;
            /
 
    2.WHILE 循环
   
        WHIEL condition LOOP
            statement;
        END LOOP;
 
        --下面使用while循环完成loop循环中的示例
           
            DECLARE
                v_s NUMBER:=0;
                v_n NUMBER:=1;
            BEGIN
                WHILE v_n<=10 LOOP
                    v_s:=v_s+v_n;
                    v_n:=v_n+1;
                END LOOP;
                DBMS_OUTPUT.PUT_LINE('1+2+3+...+10='||v_s);
            END;
            /
 
    3.FOR循环
       
        FOR loop_index IN [reverse] lowest_number ..highest_number LOOP
            statements;
        END LOOP;
       
        --下面使用for循环完成loop循环中的示例
            DECLARE
                v_s NUMBER:=0;
            BEGIN
                FOR v_n IN 1 ..10 LOOP
                    v_s:=v_s+v_n;
                    DBMS_OUTPUT.PUT_LINE(v_n);
                END LOOP;
            DBMS_OUTPUT.PUT_LINE('1+2+3+...+10='||v_s);
            END;
            /  
 
            DECLARE
                v_s NUMBER:=0;
            BEGIN
                FOR v_n IN REVERSE 1 ..10 LOOP    --注意reverse是反向循环，即从到
                    v_s:=v_s+v_n;
                    DBMS_OUTPUT.PUT_LINE(v_n);
                END LOOP;
            DBMS_OUTPUT.PUT_LINE('1+2+3+...+10='||v_s);
            END;
            /
 
四、GOTO语句
    GOTO label_name
 
        --下面使用goto语句完成loop循环中的示例
            DECLARE
                v_n NUMBER:=1;
                v_s NUMBER:=0;
            BEGIN
                LOOP
                    v_s:=v_s+v_n;
                    v_n:=v_n+1;
                    IF v_n>10 THEN
                        GOTO out;
                    END IF;
                END LOOP;
                <<out>>
                DBMS_OUTPUT.PUT_LINE('1+2+3+...+10='||v_s);
                END;
                /
 
    使用GOTO语句应注意：
        标号后至少要有一条语句
        PL/SQL块内可以相互跳转，内层块可以跳到外层块，但外层块不能跳到内层块
        不能从某一IF语句外部跳到其内部
        不能从某一循环外跳到其内部
        不能从某一子程序外跳到其内
 
五、NULL
    NULL语句不会执行任何操作，并且会直接将控制传递到下一条语句，使用NULL语句主要是提高程序的可阅读性
        --如下面的示例
            DECLARE
                v_sal emp.sal%TYPE;
                v_ename emp.ename%TYPE;
            BEGIN
                SELECT ename,sal into v_ename,v_sal
                FROM emp WHERE empno=&inputno;
                IF v_sal<3000 then
                    UPDATE emp SET comm=sal*1.2 WHERE ename=v_ename;
                ELSE
                    NULL;
                END IF;
            END;
            /
           
六、更多参考
     
有关SQL请参考
        SQL 基础--> 子查询

        SQL 基础-->多表查询
SQL基础-->分组与分组函数

SQL 基础-->常用函数

SQL 基础--> ROLLUP与CUBE运算符实现数据汇总
SQL基础-->层次化查询(START BY ... CONNECT BY PRIOR)

 

    有关PL/SQL请参考

        PL/SQL --> 语言基础

PL/SQL --> 流程控制

PL/SQL --> 存储过程

PL/SQL --> 函数

PL/SQL --> 游标

PL/SQL -->隐式游标(SQL%FOUND)

PL/SQL --> 异常处理(Exception)

PL/SQL --> PL/SQL记录

PL/SQL --> 包的创建与管理

PL/SQL --> 包重载、初始化

PL/SQL --> DBMS_DDL包的使用

PL/SQL --> DML 触发器

PL/SQL --> INSTEAD OF 触发器