如何在表上创建触发器，为每个插入的行填充 id 与 pl/sql 中序列的值？

Question

create or replace TRIGGER dept_id_trig

 BEFORE INSERT ON DEPARTMENTS


  FOR EACH ROW

DECLARE

BEGIN

  IF(:NEW.DEPARTMENT_ID IS NULL )

  THEN

   select DEPT_DEPTID_SEQ.nextval INTO :new.DEPARTMENT_ID FROM dual;

  END IF;

END; 

Answer 1

请检查以下触发器。

CREATE OR REPLACE TRIGGER dept_id_trig
  BEFORE INSERT ON DEPARTMENTS
  FOR EACH ROW
DECLARE
BEGIN
    :new.DEPARTMENT_ID := DEPT_DEPTID_SEQ.nextval;
END;

Answer 2

如果您使用的是 Oracle 12c 或更高版本，请在列上使用IDENTITY子句而不是触发器：

CREATE TABLE departments(
  department_id NUMBER(10,0)
                GENERATED ALWAYS AS IDENTITY
                CONSTRAINTS departments__department_id__pk PRIMARY KEY
)

Answer 3

这是在创建新表时由 Oracle 自身生成的触发器：

create or replace TRIGGER dept_id_trig 
BEFORE INSERT ON DEPARTMENTS 
FOR EACH ROW 
BEGIN
  <<COLUMN_SEQUENCES>>
  BEGIN
    IF INSERTING AND :NEW.DEPARTMENT_ID IS NULL THEN
      SELECT DEPT_DEPTID_SEQ.NEXTVAL INTO :NEW.DEPARTMENT_ID FROM SYS.DUAL;
    END IF;
  END COLUMN_SEQUENCES;
END;