search
HomeDatabaseOracleHow to write oracle trigger

In Oracle, a trigger will automatically execute a defined statement when the specified condition is met. The writing method is "create [or replace] tigger trigger name trigger time trigger event on table name [for each row] begin pl/sql statement end".

How to write oracle trigger

The operating environment of this tutorial: Windows 10 system, Oracle 11g version, Dell G3 computer.

How to write an oracle trigger

1. Introduction to triggers

The definition of a trigger means that when a certain condition is established, it triggers The statements defined in the container will be automatically executed.

Therefore, triggers do not need to be called manually and cannot be called.

Then, the triggering conditions of the trigger are actually set when you define it.

It needs to be explained here that triggers can be divided into statement-level triggers and row-level triggers.

For detailed introduction, please refer to the information on the Internet. Simply put, statement-level triggers can be triggered before or after the execution of certain statements. Row-level triggers are triggered once when the row data in the defined trigger table changes.

Specific examples:

1. A statement-level trigger defined in a table. When the table is deleted, the program will automatically execute the operation process defined in the trigger. This means that the operation of deleting the table is the condition for trigger execution.

2. If a row-level trigger is defined in a table, when a row of data in the table changes, such as deleting a row of records, the trigger will be automatically executed.

2. Trigger syntax

Trigger syntax:

create [or replace] tigger 触发器名 触发时间 触发事件
on 表名
[for each row]
begin
 pl/sql语句
end

Among them:

  • trigger Trigger name: The name of the trigger object. Since the trigger is automatically executed by the database, the name is just a name and has no real purpose.

  • Trigger time: Indicates when the trigger is executed. The value is optional:

  • before: Indicates that the trigger is executed before the database action;

  • after: Indicates that the trigger is executed after the database action.

  • Trigger event: Indicate which database actions will trigger this trigger:

  • insert: Database insertion will trigger this trigger;

  • update: Database modification will trigger this trigger;

  • delete: Database deletion will trigger this trigger.

  • Table name: The table where the database trigger is located.

  • for each row: The trigger is executed once for each row of the table. Without this option, it is executed only once for the entire table.

Triggers can achieve the following functions:

Function:

1. Allow/restrict modifications to the table

2. Automatically generate derived columns, such as auto-increment fields

3. Enforce data consistency

4. Provide auditing and logging

5. Prevent invalid transaction processing

6. Enable complex business logic

Example

1) The following trigger is triggered before updating the table tb_emp, in order to not allow the table to be modified on weekends:

create or replace trigger auth_secure before insert or update or DELETE
on tb_emp
begin
  IF(to_char(sysdate,'DY')='星期日') THEN
    RAISE_APPLICATION_ERROR(-20600,'不能在周末修改表tb_emp');
  END IF;
END;
/

2), use triggers to realize the serial number auto-increment

Create a test table:

create table tab_user(
  id number(11) primary key,
  username varchar(50),
  password varchar(50)
);

Create a sequence:

Copy the code The code is as follows:

create sequence my_seq increment by 1 start with 1 nomaxvalue nocycle cache 20;

Create a trigger:

CREATE OR REPLACE TRIGGER MY_TGR
 BEFORE INSERT ON TAB_USER
 FOR EACH ROW--对表的每一行触发器执行一次
DECLARE
 NEXT_ID NUMBER;
BEGIN
 SELECT MY_SEQ.NEXTVAL INTO NEXT_ID FROM DUAL;
 :NEW.ID := NEXT_ID; --:NEW表示新插入的那条记录
END;

Insert data into the table:

insert into tab_user(username,password) values('admin','admin');
insert into tab_user(username,password) values('fgz','fgz');
insert into tab_user(username,password) values('test','test');
COMMIT;

Query table results: SELECT * FROM TAB_USER;

Recommended tutorial: "Oracle Video tutorial

The above is the detailed content of How to write oracle trigger. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
什么是oracle asm什么是oracle asmApr 18, 2022 pm 04:16 PM

oracle asm指的是“自动存储管理”,是一种卷管理器,可自动管理磁盘组并提供有效的数据冗余功能;它是做为单独的Oracle实例实施和部署。asm的优势:1、配置简单、可最大化推动数据库合并的存储资源利用;2、支持BIGFILE文件等。

oracle怎么查询所有索引oracle怎么查询所有索引May 13, 2022 pm 05:23 PM

方法:1、利用“select*from user_indexes where table_name=表名”语句查询表中索引;2、利用“select*from all_indexes where table_name=表名”语句查询所有索引。

Oracle怎么查询端口号Oracle怎么查询端口号May 13, 2022 am 10:10 AM

在Oracle中,可利用lsnrctl命令查询端口号,该命令是Oracle的监听命令;在启动、关闭或重启oracle监听器之前可使用该命令检查oracle监听器的状态,语法为“lsnrctl status”,结果PORT后的内容就是端口号。

oracle全角怎么转半角oracle全角怎么转半角May 13, 2022 pm 03:21 PM

在oracle中,可以利用“TO_SINGLE_BYTE(String)”将全角转换为半角;“TO_SINGLE_BYTE”函数可以将参数中所有多字节字符都替换为等价的单字节字符,只有当数据库字符集同时包含多字节和单字节字符的时候有效。

oracle怎么删除sequenceoracle怎么删除sequenceMay 13, 2022 pm 03:35 PM

在oracle中,可以利用“drop sequence sequence名”来删除sequence;sequence是自动增加数字序列的意思,也就是序列号,序列号自动增加不能重置,因此需要利用drop sequence语句来删除序列。

oracle怎么查询数据类型oracle怎么查询数据类型May 13, 2022 pm 04:19 PM

在oracle中,可以利用“select ... From all_tab_columns where table_name=upper('表名') AND owner=upper('数据库登录用户名');”语句查询数据库表的数据类型。

oracle查询怎么不区分大小写oracle查询怎么不区分大小写May 10, 2022 pm 05:45 PM

方法:1、利用“LOWER(字段值)”将字段转为小写,或者利用“UPPER(字段值)”将字段转为大写;2、利用“REGEXP_LIKE(字符串,正则表达式,'i')”,当参数设置为“i”时,说明进行匹配不区分大小写。

Oracle怎么修改sessionOracle怎么修改sessionMay 13, 2022 pm 05:06 PM

方法:1、利用“alter system set sessions=修改后的数值 scope=spfile”语句修改session参数;2、修改参数之后利用“shutdown immediate – startup”语句重启服务器即可生效。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

Safe Exam Browser

Safe Exam Browser

Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!