PL/SQL 游标详解

2023-12-05 13:53:28

刚打开游标的时候，是位于一个空行，要用fetch into 才能到第一行。
只是要注意用更新游标的时候，不能在游标期间commit. 否则会报ORA-01002: fetch out of sequence就是COMMIT导致的错误。
在打开有for update的cursor时，系统会给取出的数据加上排他锁(exclusive), 这样在这个锁释放前其他用户不能对这些记录作update、delete和加锁。
而我一旦执行了commit,锁就释放了，游标也变成无效的,再去fetch数据时就出现错误了。因而要把commit放在循环外，等到所有数据处理完成后再commit,然后关闭cursor

隐含游标
--------
又名SQL游标，用于处理单行select into 和 DML语句。
SQL%ISOPEN
SQL%FOUND
SQL%NOTFOUND
SQL%ROWCOUNT

显示游标
--------
用户处理select语句返回的多行数据。
select语句返回多行数据处理方式：[1]显示游标；[2]select ... bulk collect into 集合变量...；

【1】显示游标属性
[1] %ISOPEN 检测游标是否打开。
[2] %FOUND 检测游标结果集是否存在数据。
[3] %NOTFOUND 是否不存在数据。
[4] %ROWCOUNT 游标已提取的实际行数

【2】使用显示游标
[1] 定义游标
CURSOR cursor_name IS select_statement;
[2] 打开游标
OPEN cursor_name;
[3] 提取数据
FECTH cursor_name INTO variable,...
[4] 关闭数据
CLOSE cursor_name;
使用标量变量：

DECLARE
Cursor emp_cur IS select ename,sal from emp order by empno;
v_ename emp.ename%TYPE;
v_sal   emp.sal%TYPE;
BEGIN
IF NOT emp_cur%ISOPEN THEN
   OPEN emp_cur; 
   DBMS_OUTPUT.PUT_LINE(‘打开游标‘);
END IF;
NULL;
LOOP
   FETCH emp_cur INTO v_ename,v_sal;
   EXIT WHEN emp_cur%NOTFOUND;
   DBMS_OUTPUT.PUT_LINE(‘用户名：‘||v_ename||‘，工资：‘||v_sal);
END LOOP;
NULL;
IF emp_cur%ISOPEN THEN
   CLOSE emp_cur;
   DBMS_OUTPUT.PUT_LINE(‘关闭游标‘);
END IF;
END;

使用PLSQL记录变量：

DECLARE
Cursor emp_cur IS select ename,sal from emp order by empno;
emp_record emp_cur%ROWTYPE;
BEGIN
IF NOT emp_cur%ISOPEN THEN
   OPEN emp_cur; 
   DBMS_OUTPUT.PUT_LINE(‘打开游标‘);
END IF;
NULL;
LOOP
   FETCH emp_cur INTO emp_record;
   EXIT WHEN emp_cur%NOTFOUND;
   DBMS_OUTPUT.PUT_LINE(‘用户名：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
END LOOP;
NULL;
IF emp_cur%ISOPEN THEN
   CLOSE emp_cur;
   DBMS_OUTPUT.PUT_LINE(‘关闭游标‘);
END IF;
END;

使用PLSQL集合变量：

DECLARE
Cursor emp_cur IS select ename,sal from emp order by empno;
TYPE emp_table_type IS TABLE OF emp_cur%ROWTYPE INDEX BY BINARY_INTEGER;
emp_table emp_table_type;
i number;
BEGIN
i := 1;
IF NOT emp_cur%ISOPEN THEN
   OPEN emp_cur; 
   DBMS_OUTPUT.PUT_LINE(‘打开游标‘);
END IF;
NULL;
LOOP
   FETCH emp_cur INTO emp_table(i);
   EXIT WHEN emp_cur%NOTFOUND;
   DBMS_OUTPUT.PUT_LINE(‘用户名：‘||emp_table(i).ename||‘，工资：‘||emp_table(i).sal);
   i := i + 1;
END LOOP;
NULL;
IF emp_cur%ISOPEN THEN
   CLOSE emp_cur;
   DBMS_OUTPUT.PUT_LINE(‘关闭游标‘);
END IF;
END;

【3】循环游标
FOR record_name IN cursor_name|select_statement LOOP
statement;

....
END LOOP;

declare 
cursor emp_cusor is select ename,sal from emp where deptno = &no order by empno;
begin
for emp_record in emp_cusor loop
      dbms_output.put_line(‘姓名：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
end loop;
end;

begin
for emp_record in (select ename,sal from scott.emp where deptno = &no order by empno) loop
      dbms_output.put_line(‘姓名：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
end loop;
end;

【4】参数游标
CURSOR cursor_name(parameter_name datatype) IS select_statement;
--只能制定类型，不能指定具体大小
OPEN cursor_name(参数值);
FECTH cursor_name INTO
variable,...;
CLOSE cursor_name;

declare 
cursor emp_cursor(v_depnto number) is select ename,sal from scott.emp where deptno = v_depnto order by empno;
emp_record emp_cursor%rowtype;
v_dno number;
begin
v_dno := &no;
if not emp_cursor%isopen then
      open emp_cursor(v_dno);
end if; 
null;
loop
        fetch emp_cursor into emp_record; 
        exit when emp_cursor%notfound;
        dbms_output.put_line(‘姓名：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
end loop;
null;
if emp_cursor%isopen then
       close emp_cursor;
end if;
end;

declare 
cursor emp_cursor(v_depnto number) is select ename,sal from scott.emp where deptno = v_depnto order by empno;
v_dno number;
begin
v_dno := &no;
for emp_record in emp_cursor(v_dno) loop
      dbms_output.put_line(‘姓名：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
end loop;
end;

【5】更新、删除游标行

CURSOR cursor_name IS select_statement
FOR UPDATE [OF column_reference] [NOWAITE]; -- OF子句指定对特定表加锁。
UPDATE table_name SET column=.. WHERE CURRENT OF cursor_name;
DELETE table_name WHERE CURRENT OF cursor_name;

declare
       cursor test_cursor is select empno,ename,sal,deptno from scott.test for update;
       test_record test_cursor%rowtype;
       v_deptno number;
       v_sal test.sal%type;
begin
       v_deptno := &no;
       if not test_cursor%isopen then
          open test_cursor;
       end if;
       loop
          fetch test_cursor into test_record;
          exit when test_cursor%notfound;
          dbms_output.put_line(‘姓名：‘||test_record.ename||‘，旧工资：‘||test_record.sal);
          if test_record.deptno = v_deptno then
             update scott.test set sal=2*sal where current of test_cursor;
          else
             update scott.test set sal=3*sal where current of test_cursor;
          end if;
       end loop;
       close test_cursor;
end;
       
declare
cursor test_cursor is select empno,ename,sal,deptno from scott.test for update;
      v_deptno NUMBER:=&dno;
begin
for test_record in test_cursor loop
        if test_record.deptno = v_deptno then
                 dbms_output.put_line(‘姓名：‘||test_record.ename||‘，旧工资：‘||test_record.sal);
                 update scott.test set sal = sal*1.5 where current of test_cursor;
           end if;
       end loop;
end;

使用游标删除数据

declare 
cursor test_cursor(v_deptno number) is select deptno,empno,ename,comm from scott.test where deptno = v_deptno for update;
v_dno test.deptno%type := &dno;
begin
     for test_record in test_cursor(v_dno) loop
         if test_record.comm is null then
            dbms_output.put_line(‘用户名：‘||test_record.ename||‘部门：‘||test_record.deptno);
            delete from scott.test where current of test_cursor;
         end if;
     end loop;     
end;

【6】游标变量
指向内存地址的指针。可以在打开游标时指定其所对应的SELECT语句，实现动态游标。
[1]定义REF CURSOR类型和游标变量：
Type ref_type_name IS REF CURSOR [RETURN return_type --必须是PL/SQL记录类型];
说明：如果指定RETURN子句，那么在打开游标时SELECT语句的返回结果必须与RETURN子句所指定的记录类型匹配。
cursor_variable ref_type_name;
SYS_REFCURSOR
[2]打开游标，指定对应的SELECT语句：
OPEN cursor_variable FOR select_statement;
[3]提取数据
FETCH cursor_variable INTO variable1,variable,...;
[4]关闭游标
CLOSE cursor_variable;

不使用RETURN子句
----------------

DECLARE
TYPE ref_type_table IS REF CURSOR;
v_cursor            ref_type_table;
emp_record          emp%rowtype;
BEGIN
     OPEN v_cursor FOR select * from emp where deptno=&no;
     LOOP
         FETCH v_cursor INTO emp_record;
         EXIT WHEN v_cursor%NOTFOUND;
         dbms_output.put_line(‘员工号：‘||emp_record.ename||‘部门号：‘||emp_record.deptno);
     END LOOP;
     CLOSE v_cursor;
END;

使用RETURN子句
--------------

DECLARE
emp_record          emp%rowtype;
TYPE ref_type_table IS REF CURSOR RETURN emp%rowtype;
v_cursor            ref_type_table;
BEGIN
     OPEN v_cursor FOR select * from emp where deptno=&no;
     LOOP
         FETCH v_cursor INTO emp_record;
         EXIT WHEN v_cursor%NOTFOUND;
         dbms_output.put_line(‘员工号：‘||emp_record.ename||‘部门号：‘||emp_record.deptno);
     END LOOP;
     CLOSE v_cursor;
END;

DECLARE
Type emp_record_type IS RECORD(
       ename emp.ename%TYPE,
       salary emp.sal%TYPE,
       deptno emp.deptno%TYPE);
emp_record emp_record_type;

TYPE ref_type_table IS REF CURSOR RETURN emp_record_type;
v_cursor            ref_type_table;
BEGIN
     OPEN v_cursor FOR select ename,sal,deptno from emp where deptno=&no;
     LOOP
         FETCH v_cursor INTO emp_record;
         EXIT WHEN v_cursor%NOTFOUND;
         dbms_output.put_line(‘员工号：‘||emp_record.ename||‘，部门号：‘||emp_record.deptno||‘，工资：‘||emp_record.salary);
     END LOOP;
     CLOSE v_cursor;
END;

【7】使用游标批量获取
FETCH ... BULK COLLECT INTO ...[LIMIT row_number];

不限制行数
----------

DECLARE
     CURSOR emp_cursor(v_deptno number) IS SELECT * FROM EMP WHERE deptno = v_deptno;
     TYPE type_emp_table IS TABLE OF emp%ROWTYPE INDEX BY BINARY_INTEGER;
     emp_table type_emp_table;
     v_dno emp.deptno%TYPE;
BEGIN
     v_dno := &no;
     OPEN emp_cursor(v_dno);
     FETCH emp_cursor BULK COLLECT INTO emp_table;
     CLOSE emp_cursor;
     FOR i IN 1..emp_table.COUNT LOOP
         dbms_output.put_line(‘员工号：‘||emp_table(i).ename||‘工资：‘||emp_table(i).sal);
     END LOOP;
     CLOSE emp_cursor;
END;

限制行数
--------

DECLARE
     CURSOR emp_cursor(v_deptno number) IS SELECT * FROM EMP WHERE deptno = v_deptno;
     TYPE type_emp_table IS TABLE OF emp%ROWTYPE INDEX BY BINARY_INTEGER;
     emp_table type_emp_table;
     v_dno emp.deptno%TYPE;
BEGIN
     v_dno := &no;
     OPEN emp_cursor(v_dno);
     FETCH emp_cursor BULK COLLECT INTO emp_table LIMIT &2;
     CLOSE emp_cursor;
     FOR i IN 1..emp_table.COUNT LOOP
         dbms_output.put_line(‘员工号：‘||emp_table(i).ename||‘工资：‘||emp_table(i).sal);
     END LOOP;
     CLOSE emp_cursor;
END;

【8】使用CURSOR表达式
作用嵌套游标。

DECLARE
       CURSOR dept_emp_cursor(v_deptno number) IS 
   SELECT dname,cursor(SELECT * FROM emp e WHERE e.deptno = d.deptno) 
   FROM dept d WHERE deptno = v_deptno;
       TYPE emp_cursor_type IS REF CURSOR;
       emp_cursor emp_cursor_type;
       emp_record emp%ROWTYPE;
       v_name dept.dname%TYPE;
       v_dno emp.deptno%TYPE;
BEGIN
     v_dno := &no;
     OPEN dept_emp_cursor(v_dno);
     loop 
          FETCH dept_emp_cursor INTO v_name,emp_cursor;
          EXIT WHEN dept_emp_cursor%NOTFOUND;
          dbms_output.put_line(‘部门名称：‘||v_name);
          LOOP
              FETCH emp_cursor INTO emp_record;            
              EXIT WHEN emp_cursor%NOTFOUND;
              dbms_output.put_line(‘员工名称：‘||emp_record.ename||‘，工资：‘||emp_record.sal);
          END LOOP;
     end loop;
     CLOSE dept_emp_cursor;
END;

PL/SQL 游标详解,布布扣,bubuko.com

PL/SQL 游标详解

码农公寓

相关文章