如何在plsql中使用绑定变量？

Question

简单的任务

variable dept_id NUMBER

DECLARE
    max_deptno NUMBER;
    dept_name departments.department_name%TYPE := 'Education';
BEGIN
    select max(department_id)
      into max_deptno
      from departments;
    :dept_id := max_deptno + 10;
    insert into departments (department_id, department_name, location_id)
      values (:dept_id, dept_name, null);
    DBMS_OUTPUT.PUT_LINE('The maximum department id is ' || max_deptno);
    DBMS_OUTPUT.PUT_LINE('Rows made by insert: ' || SQL%ROWCOUNT);
END;

max_deptno不是NULL.为什么dept_id在赋值后为NULL？我究竟做错了什么？

脚本输出:

MAX(DEPARTMENT_ID)
------------------
               520 

Error starting at line 10 in command:
DECLARE
max_deptno NUMBER;
dept_name departments.department_name%TYPE := 'Education1';
BEGIN
select max(department_id)
into max_deptno
from departments;
:dept_id := max_deptno + 10;
insert into departments (department_id, department_name, location_id)
values (:dept_id, dept_name, null);
DBMS_OUTPUT.PUT_LINE('The maximum department id is ' || max_deptno);
DBMS_OUTPUT.PUT_LINE('Rows made by insert: ' || SQL%ROWCOUNT);
END;

错误报告:

ORA-01400: ?????????? ???????? NULL ? ("ANDKOM"."DEPARTMENTS"."DEPARTMENT_ID")
ORA-06512: ??  line 9
01400. 00000 -  "cannot insert NULL into (%s)"
*Cause:    
*Action:

Answer 1

DEPT_ID赋值后,宿主变量不为NULL.问题是您的INSERT语句正在使用局部变量NEW_DPT,INSERT并且该局部变量尚未赋值.如果你真的想在PL/SQL中使用主机变量(在现实生活中你基本上不会这样做),你需要在PL/SQL块中使用它

SQL> ed
Wrote file afiedt.buf

  1  DECLARE
  2    max_deptno NUMBER;
  3    new_dpt NUMBER;
  4    dept_name departments.department_name%TYPE := 'Education';
  5  BEGIN
  6    select max(department_id)
  7      into max_deptno
  8      from departments;
  9    :dept_id := max_deptno + 10;
 10    insert into departments (department_id, department_name, location_id)
 11      values (:dept_id, dept_name, null);
 12    DBMS_OUTPUT.PUT_LINE('The maximum department id is ' || max_deptno);
 13    DBMS_OUTPUT.PUT_LINE('Rows made by insert: ' || SQL%ROWCOUNT);
 14* END;
SQL> /
The maximum department id is 270
Rows made by insert: 1

PL/SQL procedure successfully completed.

SQL> select :dept_id from dual;

  :DEPT_ID
----------
       280

然而,更现实的是完全抛弃替代变量

SQL> ed
Wrote file afiedt.buf

  1  DECLARE
  2    max_deptno NUMBER;
  3    new_dpt NUMBER;
  4    dept_name departments.department_name%TYPE := 'Education';
  5  BEGIN
  6    select max(department_id)
  7      into max_deptno
  8      from departments;
  9    new_dpt := max_deptno + 10;
 10    insert into departments (department_id, department_name, location_id)
 11      values (new_dpt, dept_name, null);
 12    DBMS_OUTPUT.PUT_LINE('The maximum department id is ' || max_deptno);
 13    DBMS_OUTPUT.PUT_LINE('Rows made by insert: ' || SQL%ROWCOUNT);
 14* END;
SQL> /
The maximum department id is 280
Rows made by insert: 1

PL/SQL procedure successfully completed.