关系型数据库大王Mysql——SQL编程

FJW0208142026-01-29 9:31

SQL编程

触发器

什么是触发器?

​ 当某个表的数据发生某件事(insert, delete, update), 然后自动触发预先编译好的若干条sql

触发器

1.特点：触发的操作和触发器的sql语句是一个事务操作，具备原子性，要么都执行，要么都不执行

2.作用：保证数据的完整性，起到约束的作用

示例1

复制代码 
mysql> create table emp_count(
    -> emp_count_id int primary key auto_increment,
    -> total int);
Query OK, 0 rows affected (0.07 sec)

mysql> show tables;
+--------------------+
| Tables_in_dml_test |
+--------------------+
| department         |
| emp_count          |
| employee           |
| user               |
+--------------------+
4 rows in set (0.00 sec)

mysql> insert into emp_count values(1,0);
Query OK, 1 row affected (0.01 sec)

mysql> select * from emp_count;
+--------------+-------+
| emp_count_id | total |
+--------------+-------+
|            1 |     0 |
+--------------+-------+
1 row in set (0.00 sec)

mysql> update emp_count set total = 18 where total = 0;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp_count;
+--------------+-------+
| emp_count_id | total |
+--------------+-------+
|            1 |    18 |
+--------------+-------+
1 row in set (0.00 sec)

#临时修改终止符，以免与触发器语句发生冲突
mysql> \d $		#delimiter $
mysql> create trigger emp_count_p after insert
    -> on employee for each row
    -> begin
    -> update emp_count set total = total + 1 where emp_count_id = 1;
    -> end
    -> $
Query OK, 0 rows affected (0.01 sec)

mysql> show triggers\G
*************************** 1. row ***************************
             Trigger: emp_count_p
               Event: INSERT
               Table: employee
           Statement: begin
update emp_count set total = total + 1 where emp_count_id = 1;
end
              Timing: AFTER
             Created: 2025-11-18 20:10:20.59
            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@%
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
1 row in set (0.01 sec)

mysql> insert into employee(number,name) values("23123213132",'来俊希')$
Query OK, 1 row affected (0.01 sec)

mysql> select * from emp_count$
+--------------+-------+
| emp_count_id | total |
+--------------+-------+
|            1 |    19 |
+--------------+-------+
1 row in set (0.00 sec)

示例2

复制代码 
mysql> create table bank(
    -> b_id int primary key auto_increment,
    -> value int)$
Query OK, 0 rows affected (0.03 sec)

mysql> create table u(
    -> u_id int primary key auto_increment,
    -> value int)$
Query OK, 0 rows affected (0.04 sec)

#创建触发器
mysql> create trigger u_bank_t after insert
    -> on u for each row
    -> begin
    -> update bank set value = value + 500 where b_id = 1;
    -> end
    -> $
Query OK, 0 rows affected (0.02 sec)

#查看创建的触发器
mysql> show triggers\G
*************************** 1. row ***************************
             Trigger: emp_count_p
               Event: INSERT
               Table: employee
           Statement: begin
update emp_count set total = total + 1 where emp_count_id = 1;
end
              Timing: AFTER
             Created: 2025-11-18 20:10:20.59
            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@%
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
*************************** 2. row ***************************
             Trigger: u_bank_t
               Event: INSERT
               Table: u
           Statement: begin
update bank set value = value + 500 where b_id = 1;
end
              Timing: AFTER
             Created: 2025-11-18 20:24:50.28
            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@%
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
2 rows in set (0.00 sec)

mysql> insert into bank(b_id,value) values(1,0);
Query OK, 1 row affected (0.01 sec)

mysql> select * from bank;
+------+-------+
| b_id | value |
+------+-------+
|    1 |     0 |
+------+-------+
1 row in set (0.00 sec)

mysql> insert into u(u_id,value) values(1,500);
Query OK, 1 row affected (0.01 sec)

mysql> select * from bank;
+------+-------+
| b_id | value |
+------+-------+
|    1 |   500 |
+------+-------+
1 row in set (0.00 sec)

mysql> select * from u;
+------+-------+
| u_id | value |
+------+-------+
|    1 |   500 |
+------+-------+
1 row in set (0.00 sec)

mysql> select value from u where u_id = 1;
+-------+
| value |
+-------+
|   500 |
+-------+
1 row in set (0.00 sec)

mysql> select value from u  group by u_id having max(value);
+-------+
| value |
+-------+
|   500 |
+-------+
1 row in set (0.00 sec)

mysql> insert into bank(value) select value from u  group by u_id having max(value);
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select * from bank;
+------+-------+
| b_id | value |
+------+-------+
|    1 |   500 |
|    2 |   500 |
+------+-------+
2 rows in set (0.00 sec)

存储过程

什么是存储过程

事先经过编译并存储在数据库中的一段sql语句集合

示例1

mysql 复制代码 
mysql> create procedure emp_count()
    -> begin
    -> select count(emp_count_id) from emp_count;
    -> end
    -> $
Query OK, 0 rows affected (0.01 sec)

#查看创建的存储过程
mysql> show create procedure emp_count\G$
*************************** 1. row ***************************
           Procedure: emp_count
            sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
    Create Procedure: CREATE DEFINER=`root`@`%` PROCEDURE `emp_count`()
begin
select count(emp_count_id) from emp_count;
end
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

#调用存储过程
mysql> call emp_count();
    -> $
+---------------------+
| count(emp_count_id) |
+---------------------+
|                   1 |
+---------------------+
1 row in set (0.00 sec)

示例2

mysql 复制代码 
mysql> create table t1(
    -> id int primary key auto_increment,
    -> password varchar(255));
    -> $
Query OK, 0 rows affected (0.03 sec)

mysql> create procedure insert_many_date(in total_row)
    -> begin
    -> declare i int  default 1;
    -> while (i < rows) do
    -> insert into t1 values(i,md5(i));
    -> set i = i + 1;
    -> end while;
    -> end
    -> $
    
mysql> create procedure user_password(in pwd varchar(255))
    -> begin
    -> select * from user where password = pwd;
    -> end$
Query OK, 0 rows affected (0.01 sec)

mysql> call user_password("111")$
Empty set (0.01 sec)

示例3

mysql 复制代码 
mysql> select * from user;
    -> $
+---------+----------+----------+------+------------+
| user_id | username | password | name | hire_date  |
+---------+----------+----------+------+------------+
|       1 | ljx      | ljxbbfjw | cj   | 2006-06-06 |
|       2 | ljx      | ljxbbfjw | cj   | 2006-06-06 |
|       3 | lisi     | 123      | ls   | 2007-07-07 |
|       4 | wangwu   | 123      | ww   | 2008-08-08 |
|       5 | cj       | 123      | cj   | 2009-09-09 |
+---------+----------+----------+------+------------+
5 rows in set (0.00 sec)

mysql> create procedure user_password(in pwd varchar(255))
    -> begin
    -> select * from user where password = pwd;
    -> end$
Query OK, 0 rows affected (0.01 sec)

mysql> call user_password("123")$
+---------+----------+----------+------+------------+
| user_id | username | password | name | hire_date  |
+---------+----------+----------+------+------------+
|       3 | lisi     | 123      | ls   | 2007-07-07 |
|       4 | wangwu   | 123      | ww   | 2008-08-08 |
|       5 | cj       | 123      | cj   | 2009-09-09 |
+---------+----------+----------+------+------------+
3 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

示例4

mysql 复制代码 
mysql> select @a;
    -> $
+------------+
| @a         |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)

mysql> set @a = 1;
    -> $
Query OK, 0 rows affected (0.01 sec)

mysql> select @a;
    -> $
+------+
| @a   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql> \d $
mysql> create procedure user_count_a(out number int)
    -> begin
    -> select count(1) into number from user;
    -> end$
Query OK, 0 rows affected (0.01 sec)

mysql> show create procedure user_count_a\G$
*************************** 1. row ***************************
           Procedure: user_count_a
            sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
    Create Procedure: CREATE DEFINER=`root`@`%` PROCEDURE `user_count_a`(out number int)
begin
select count(1) into number from user;
end
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> call user_count_a(@a);
    -> $
Query OK, 1 row affected (0.01 sec)

mysql> select @a
    -> $
+------+
| @a   |
+------+
|    5 |
+------+
1 row in set (0.00 sec)

mysql> \d ;

mysql> select count(1) from user;
+----------+
| count(1) |
+----------+
|        5 |
+----------+
1 row in set (0.00 sec)

示例5

mysql 复制代码 
mysql> \d $
mysql> create procedure count_emp_name(in dep_name varchar(255),out count_emp int)
    -> begin
    -> select count(*) into count_emp from employee where department_NO = (select number from department where name = dep_name);
    -> end$
Query OK, 0 rows affected (0.02 sec)

mysql> \d ;

mysql> show create procedure count_emp_name\G;
*************************** 1. row ***************************
           Procedure: count_emp_name
            sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
    Create Procedure: CREATE DEFINER=`root`@`%` PROCEDURE `count_emp_name`(in dep_name varchar(255),out count_emp int)
begin
select count(*) into count_emp from employee where department_NO = (select number from department where name = dep_name);
end
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  Database Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> call count_emp_name("上海中心",@a);
Query OK, 1 row affected (0.00 sec)

mysql> select @a
    -> ;
+------+
| @a   |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

mysql> select count(*) from employee where department_NO = (select number from department where name = "上海中心");
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)
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