1)触发器只能建立在永久表(Permanent Table)上,不能对临时表(Temporary Table)建立触发器。sql
# 建立触发器,单条执行语句 # create trigger 触发器名 // 不能与已存在的触发器重复 触发时间 // before、after,表示事件以前或以后触发 触发事件 // insert、update、delete 触发该触发器的具体事件 on 触发器响应表名 // 该触发器操做的表 for each row 触发操做; > create trigger trigger_student_count_insert after insert on student for each row update student_count set scount = scount + 1; Query OK, 0 rows affected (0.09 sec)
# 建立触发器,多条执行语句 # delimiter $$ // 定义结束符 create trigger 触发器名 // 不能与已存在的触发器重复 触发时间 // before、after,表示事件以前或以后触发 触发事件 // insert、update、delete 触发该触发器的具体事件 on 触发器响应表名 // 该触发器操做的表 for each row begin 触发操做(多条执行语句); // 每条语句使用分号结束 end $$ // 使用自定义结束符 > delimiter $$ > create trigger trigger_student_count_insert after insert on student for each row begin update student_count set scount = scount + 1; update student_count set scount = scount + 1000; end $$ Query OK, 0 rows affected (0.10 sec)
2)对同一个表相同触发时间的相同触发事件,只能定义一个触发器。数据库
3)使用别名 old 和 new 来引用触发器中发生变化的记录内容,这与其余的数据库是类似的。函数
别名 | 解释 |
---|---|
new | 在触发器为 insert 事件类型时有效,表示当前正在插入的数据,如 new.class |
old | 在触发器为 delete 事件类型时有效,表示当前正在删除的数据,如 old.class |
> delimiter $$ create trigger ins_film after insert on film for each row begin insert into film_text (film_id, title, description) values (new.film_id, new.title, new.description); end; $$
一次能够删除一个触发程序,若是没有指定 schema_name,默认为当前数据库。ui
# 删除触发器 # drop trigger [schema_name.]触发器名; > drop trigger trigger_student_count_insert; Query OK, 0 rows affected (0.00 sec) # 删除触发器,若是触发器存在就删除 # drop trigger if exists 触发器名; > drop trigger if exists trigger_student_count_insert;
能够经过执行 show triggers 命令查看全部触发器的状态、语法等信息。this
# 查看全部的触发器 > show triggers; *************************** 1. row *************************** Trigger: trigger_student_count_insert Event: INSERT Table: student Statement: begin update student_count set scount = scount + 1; update student_count set scount = scount + 1000; end Timing: AFTER Created: 2018-06-28 18:42:15.47 sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE, NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION Definer: root@localhost character_set_client: utf8mb4 collation_connection: utf8mb4_0900_ai_ci Database Collation: gbk_chinese_ci *************************** 2. row *************************** ... ... row in set (0.01 sec)
能够经过查询系统表的 information_schema.triggers 表的方式查询指定触发器的指定信息。设计
> use information_schema; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed > desc triggers; +----------------------------+----------------------------------+------+-----+----------------------+--------------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------------------+----------------------------------+------+-----+----------------------+--------------------------------+ | TRIGGER_CATALOG | varchar(64) | NO | | NULL | | | TRIGGER_SCHEMA | varchar(64) | NO | | NULL | | | TRIGGER_NAME | varchar(64) | NO | | NULL | | | EVENT_MANIPULATION | enum('INSERT','UPDATE','DELETE') | NO | | NULL | | | EVENT_OBJECT_CATALOG | varchar(64) | NO | | NULL | | | EVENT_OBJECT_SCHEMA | varchar(64) | NO | | NULL | | | EVENT_OBJECT_TABLE | varchar(64) | NO | | NULL | | | ACTION_ORDER | int(10) unsigned | NO | | NULL | | | ACTION_CONDITION | binary(0) | YES | | NULL | | | ACTION_STATEMENT | longtext | NO | | NULL | | | ACTION_ORIENTATION | varchar(3) | NO | | | | | ACTION_TIMING | enum('BEFORE','AFTER') | NO | | NULL | | | ACTION_REFERENCE_OLD_TABLE | binary(0) | YES | | NULL | | | ACTION_REFERENCE_NEW_TABLE | binary(0) | YES | | NULL | | | ACTION_REFERENCE_OLD_ROW | varchar(3) | NO | | | | | ACTION_REFERENCE_NEW_ROW | varchar(3) | NO | | | | | CREATED | timestamp(2) | NO | | CURRENT_TIMESTAMP(2) | on update CURRENT_TIMESTAMP(2) | | SQL_MODE | set('REAL_AS_FLOAT', 'PIPES_AS_CONCAT', 'ANSI_QUOTES', 'IGNORE_SPACE', 'NOT_USED', 'ONLY_FULL_GROUP_BY', 'NO_UNSIGNED_SUBTRACTION', 'NO_DIR_IN_CREATE', 'NOT_USED_9', 'NOT_USED_10', 'NOT_USED_11', 'NOT_USED_12', 'NOT_USED_13', 'NOT_USED_14', 'NOT_USED_15', 'NOT_USED_16', 'NOT_USED_17', 'NOT_USED_18', 'ANSI', 'NO_AUTO_VALUE_ON_ZERO', 'NO_BACKSLASH_ESCAPES', 'STRICT_TRANS_TABLES', 'STRICT_ALL_TABLES', 'NO_ZERO_IN_DATE', 'NO_ZERO_DATE', 'INVALID_DATES', 'ERROR_FOR_DIVISION_BY_ZERO', 'TRADITIONAL', 'NOT_USED_29', 'HIGH_NOT_PRECEDENCE', 'NO_ENGINE_SUBSTITUTION', 'PAD_CHAR_TO_FULL_LENGTH') | NO | | NULL | | | DEFINER | varchar(93) | NO | | NULL | | | CHARACTER_SET_CLIENT | varchar(64) | NO | | NULL | | | COLLATION_CONNECTION | varchar(64) | NO | | NULL | | | DATABASE_COLLATION | varchar(64) | NO | | NULL | | +----------------------------+----------------------------------+------+-----+----------------------+--------------------------------+ 22 rows in set (0.00 sec)
# 查询指定触发器 > select * from triggers where trigger_name = 'trigger_student_count_insert' \G *************************** 1. row *************************** TRIGGER_CATALOG: def TRIGGER_SCHEMA: test TRIGGER_NAME: trigger_student_count_insert EVENT_MANIPULATION: INSERT EVENT_OBJECT_CATALOG: def EVENT_OBJECT_SCHEMA: test EVENT_OBJECT_TABLE: student ACTION_ORDER: 1 ACTION_CONDITION: NULL ACTION_STATEMENT: begin update student_count set scount = scount + 1; update student_count set scount = scount + 1000; end ACTION_ORIENTATION: ROW ACTION_TIMING: AFTER ACTION_REFERENCE_OLD_TABLE: NULL ACTION_REFERENCE_NEW_TABLE: NULL ACTION_REFERENCE_OLD_ROW: OLD ACTION_REFERENCE_NEW_ROW: NEW CREATED: 2018-06-28 18:42:15.47 SQL_MODE: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION DEFINER: root@localhost CHARACTER_SET_CLIENT: utf8mb4 COLLATION_CONNECTION: utf8mb4_0900_ai_ci DATABASE_COLLATION: gbk_chinese_ci 1 row in set (0.00 sec)
触发器执行的语句有如下两个限制。code
触发器触发顺序orm
MySQL 的触发器是按照 before 触发器、行操做、after 触发器的顺序执行的,其中任何一步操做发生错误都不会继续执行剩下的操做。若是是对事务表进行的操做,那么会整个做为一个事务被回滚(Rollback),可是若是是对非事务表进行的操做,那么已经更新的记录将没法回滚,这也是设计触发器的时候须要注意的问题 。对象
对于那些实际执行 update 操做的记录,仍然会执行 before insert 触发器的内容,在设计触发器的时候必定要考虑这种状况,避免错误地触发了触发器。事件