Oracle触发器和MySQL触发器之间的区别
Oracle触发器格式：
CREATE [OR REPLACE] TRIGGER trigger_name BEFORE|AFTER INSERT|UPDATE|DELETE ON table_name [FOR EACH ROW] DECLARE arg_name type [CONSTANT] [NOT NULL] [:=value] BEGIN pl/sql语句 END
MySQL触发器格式：
CREATE TRIGGER trigger_name BEFORE|AFTER INSERT|UPDATE|DELETE ON table_name [FOR EACH ROW] BEGIN DECLARE arg_name1[,arg_name2,...] type [DEFAULT value] sql语句 END
创建测试表（建表语句适用于Oracle、MySQL）：
CREATE TABLE test( id int, name varchar(10), age int, birthday date, description varchar(50), PRIMARY KEY (id) ); CREATE TABLE test_log( id int, dealtime date, dealtype varchar(10), PRIMARY KEY (`id`) );
Oracle触发器和MySQL触发器的区别如下：
1，创建语句格式不同
Oracle：create or replace（Oracle客户端需要手动提交，MySQL客户端设置的自动提交）
SQL> CREATE OR REPLACE TRIGGER trigger_test_insert
2 BEFORE INSERT ON test
3 FOR EACH ROW
4 BEGIN
5 insert into test_log values(1,sysdate,'insert');
6 END;
7 /
Trigger created
SQL> insert into test(id, name) values(1, 'name');
1 row inserted
SQL> commit;
Commit complete
SQL> select * from test_log;
ID DEALTIME DEALTYPE
--------------------------------------- ----------- ----------
1 2014/7/16 1 insert
MySQL：不包含or replace
mysql> delimiter $ CREATE TRIGGER trigger_test_insert BEFORE INSERT ON test FOR EACH ROW BEGIN insert into test_log values(1,now(),'insert'); END$ delimiter ; Query OK, 0 rows affected mysql> insert into test(id, name) values(1, 'name'); Query OK, 1 row affected mysql> select * from test_log; +----+------------+----------+ | id | dealtime | dealtype | +----+------------+----------+ | 1 | 2014-07-16 | insert | +----+------------+----------+ 1 row in set
2，变量的声明位置、声明格式均不相同
Oracle：声明位置在触发时的执行语句块外部
通过%type的方式将变量与表特定字段类型相关联的好处是：在某些情况下，修改该字段类型时不需要修改触发器（如：字段类型由varchar(10)修改为varchar(20)时，不需要修改触发器）
SQL> CREATE TRIGGER trigger_test_insert
2 BEFORE INSERT ON test
3 FOR EACH ROW
4 DECLARE id1 int default 1;
5 id2 int:=1;
6 id3 test_log.id%type:=1;
7 BEGIN
8 insert into test_log values(id1+id2+id3,sysdate,'insert');
9 END;
10 /
Trigger created
SQL> insert into test(id, name) values(1, 'name');
1 row inserted
SQL> commit;
Commit complete
SQL> select * from test_log;
ID DEALTIME DEALTYPE
--------------------------------------- ----------- ----------
3 2014/7/16 1 insert
MySQL：声明位置在触发时的执行语句块内部
mysql> delimiter $ CREATE TRIGGER trigger_test_insert BEFORE INSERT ON test FOR EACH ROW BEGIN DECLARE id1 int DEFAULT 1; DECLARE id2 int DEFAULT 1; insert into test_log values(id1+id2,now(),'insert'); END$ delimiter ; Query OK, 0 rows affected mysql> insert into test(id, name) values(1, 'name'); Query OK, 1 row affected mysql> select * from test_log; +----+------------+----------+ | id | dealtime | dealtype | +----+------------+----------+ | 2 | 2014-07-16 | insert | +----+------------+----------+ 1 row in set
3，注释符不同
Oracle：使用/* */作为注释符，或者两个连续的-作为注释符（PL/SQL块中至少包含一条可执行语句）
CREATE OR REPLACE TRIGGER trigger_test_insert BEFORE INSERT ON test FOR EACH ROW BEGIN --just a test /* just a test */ null; END; /
MySQL：使用/* */作为注释符，或者两个连续的-后加一个空格作为注释符
delimiter $ CREATE TRIGGER trigger_test_insert BEFORE INSERT ON test FOR EACH ROW BEGIN /* just a test */ -- 两个‘-’后面必须带空格 END$ delimiter ;
4，赋值语法不同
Oracle：可以通过select into语句赋值，还可以通过:=进行赋值
SQL> CREATE OR REPLACE TRIGGER trigger_test_insert
2 BEFORE INSERT ON test
3 FOR EACH ROW
4 DECLARE id int;
5 BEGIN
6 select max(tl.id) into id from test_log tl;
7 if id is null then
8 id:=1;
9 else
10 id:=id+1;
11 end if;
12 insert into test_log values(id,sysdate,'insert');
13 END;
14 /
Trigger created
SQL> insert into test(id, name) values(1, 'name');
1 row inserted
SQL> commit;
Commit complete
SQL> select * from test_log;
ID DEALTIME DEALTYPE
--------------------------------------- ----------- ----------
1 2014/7/16 1 insert
MySQL：可以通过select into语句赋值，还可以通过set语句进行赋值
mysql> delimiter $ CREATE TRIGGER trigger_test_insert BEFORE INSERT ON test FOR EACH ROW BEGIN DECLARE id int; select max(tl.id) into id from test_log tl; if id is null then set id=1; else set id=id+1; end if; insert into test_log values(id,now(),'insert'); END$ delimiter ; Query OK, 0 rows affected mysql> insert into test(id, name) values(1, 'name'); Query OK, 1 row affected mysql> select * from test_log; +----+------------+----------+ | id | dealtime | dealtype | +----+------------+----------+ | 1 | 2014-07-16 | insert | +----+------------+----------+ 1 row in set
5，对于行级更新触发器
Oracle：原有行用:old表示，新行用:new表示
SQL> CREATE OR REPLACE TRIGGER trigger_test_update
2 BEFORE UPDATE ON test
3 FOR EACH ROW
4 BEGIN
5 :new.description := 'change name[' ||
6 :old.name || ']->[' ||
7 :new.name || ']';
8 END;
9 /
Trigger created
SQL> insert into test(id, name) values (1, 'aaa');
1 row inserted
SQL> commit;
Commit complete
SQL> update test set name = 'bbb' where id = 1;
1 row updated
SQL> commit;
Commit complete
SQL> select id, name, description from test;
ID NAME DESCRIPTION
--------------------------------------- ---------- ----------------------
1 bbb change name[aaa]->[bbb]
MySQL：原有行用old表示，新行用new表示
mysql> delimiter $
CREATE TRIGGER trigger_test_update
BEFORE UPDATE ON test
FOR EACH ROW
BEGIN
set new.description = concat('change name[',
old.name,']->[',new.name,']');
END$
delimiter ;
Query OK, 0 rows affected
mysql> insert into test(id, name) values (1, 'aaa');
Query OK, 1 row affected
mysql> update test set name = 'bbb' where id = 1;
Query OK, 1 row affected
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select id, name, description from test;
+----+------+-------------------------+
| id | name | description |
+----+------+-------------------------+
| 1 | bbb | change name[aaa]->[bbb] |
+----+------+-------------------------+
1 row in set
6，其它一些语法、函数上的区别
Oracle：使用if...elsif...else
MySQL：使用if...elseif...else
Oracle：sysdate指代系统时间
MySQL：sysdate()指代系统时间