触发器下/存储过程/自定义函数

MySQL学习笔记(Day014:触发器下/存储过程/自定义函数)

@(MySQL学习)

[TOC]

一. 作业讲解

  • 查询employees表中非基层用户的最近详细信息

    关于Group By在《SQL必知必会》中提及的部分规定:

    1. GROUP BY子句中列出的每一列都必须是检索列或有效的表达式(但不能是聚集函数)。如果在SELECT中使用表达式,则必须在GROUP BY子句中指定相同的表达式。不能使用别名。
    2. 除聚集计算语句外,SELECT语句中的每一列都必须在GROUP BY子句中给出
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SELECT 
e.emp_no,
CONCAT(last_name, ' ', first_name) AS name,
t.title,
dp.dept_name,
s.salary
FROM
employees e
LEFT JOIN
dept_manager d ON e.emp_no = d.emp_no
LEFT JOIN
(SELECT
emp_no, title, from_date, to_date
FROM
titles
WHERE
(emp_no , from_date, to_date) IN (SELECT
emp_no, MAX(from_date), MAX(to_date)
FROM
titles AS b
GROUP BY b.emp_no)) t ON t.emp_no = e.emp_no
LEFT JOIN
(SELECT
dept_no, emp_no, from_date, to_date
FROM
dept_emp
WHERE
(emp_no , from_date, to_date) IN (SELECT
emp_no, MAX(from_date), MAX(to_date)
FROM
dept_emp AS b
GROUP BY b.emp_no)) de ON de.emp_no = e.emp_no
LEFT JOIN
(SELECT
emp_no, salary, from_date, to_date
FROM
salaries
WHERE
(emp_no , from_date, to_date) IN (SELECT
emp_no, MAX(from_date), MAX(to_date)
FROM
salaries AS b
GROUP BY b.emp_no)) s ON s.emp_no = e.emp_no
LEFT JOIN
departments dp ON dp.dept_no = de.dept_no
WHERE
d.emp_no IS NULL;
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--
-- 改进的子查询语句 - 1
--
SELECT
emp_no, title, from_date, to_date
FROM
titles
WHERE
(emp_no , from_date, to_date) IN
(
SELECT
emp_no, MAX(from_date), MAX(to_date) -- 因为数据本身的问题,这里from_date和to_date都要
FROM
titles AS b
GROUP BY b.emp_no
) -- 这个子查询表示以emp_no分类,找到最大(最近)的from_date和to_date
-- 而where条件在这个最大的基础上,过滤出我们要的title。(salary同理)


--
-- 改进的子查询语句 - 2
--
SELECT
emp_no, title, from_date, to_date
FROM
titles AS a
WHERE
(from_date, to_date) = (SELECT
MAX(from_date), MAX(to_date) -- 同样使用from_date和to_date
FROM
titles AS b
WHERE
a.emp_no = b.emp_no -- 这个是一个关联子查询
GROUP BY b.emp_no);
  • Rank排名一条SQL语句
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mysql> select * from test_rank_2;
+------+-------+
| id | score |
+------+-------+
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 30 |
| 5 | 40 |
| 6 | 40 |
+------+-------+
6 rows in set (0.00 sec)

mysql> select id, score,
-> case
-> when @prev_value = score then @rank_count
-> when @prev_value := score then @rank_count := @rank_count + 1
-> end as rank_column
-> from test_rank_2, (select @prev_value:=NULL, @rank_count:=0) as t -- 和RowNumber思路一样,增加一个表
-> order by score desc;
+------+-------+-------------+
| id | score | rank_column |
+------+-------+-------------+
| 5 | 40 | 1 |
| 6 | 40 | 1 |
| 3 | 30 | 2 |
| 4 | 30 | 2 |
| 2 | 20 | 3 |
| 1 | 10 | 4 |
+------+-------+-------------+
6 rows in set (0.00 sec)

二. 触发器 ・ 下

1. 触发器总结

  • 触发器对性能有损耗,应当非常慎重使用;
  • 对于事物表,触发器执行失败则整个语句回滚
  • Row格式主从复制,触发器不会在从库上执行
    • 因为从库复制的肯定是主库已经提交的数据,既然已经提交了说明触发器已经被触发过了,所以从库不会执行。
  • 使用触发器时应防止递归执行;

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    delimiter //
    create trigger trg_test
    before update on 'test_trigger'
    for each row
    begin
    update test_trigger set score=20 where name = old.name; -- 又触发了update操作,循环触发了
    end;//

2. 触发器模拟物化视图

  • 物化视图的概念

    • 不是基于基表的虚表
    • 根据基表实际存在的实表
    • 预先计算并保存耗时较多的SQL操作结果(如多表链接(join)或者group by等)
  • 模拟物化视图

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mysql> create table Orders  
-> (order_id int unsigned not null auto_increment,
-> product_name varchar(30) not null,
-> price decimal(8,2) not null,
-> amount smallint not null,
-> primary key(order_id));
Query OK, 0 rows affected (0.13 sec) -- 创建Orders表

mysql> insert into Orders values
-> (null, 'cpu', 135.5 ,1),
-> (null, 'memory', 48.2, 3),
-> (null, 'cpu', 125.6, 3),
-> (null, 'cpu', 105.3, 4);
Query OK, 4 rows affected (0.06 sec) -- 插入测试数据
Records: 4 Duplicates: 0 Warnings: 0

mysql> select * from Orders;
+----------+--------------+--------+--------+
| order_id | product_name | price | amount |
+----------+--------------+--------+--------+
| 1 | cpu | 135.50 | 1 |
| 2 | memory | 48.20 | 3 |
| 3 | cpu | 125.60 | 3 |
| 4 | cpu | 105.30 | 4 |
+----------+--------------+--------+--------+
4 rows in set (0.00 sec)

-- 建立一个模拟物化视图的表(即用这张表来模拟物化视图)
mysql> create table Orders_MV
-> ( product_name varchar(30) not null,
-> price_sum decimal(8,2) not null,
-> amount_sum int not null,
-> price_avg float not null,
-> orders_cnt int not null,
-> unique index (product_name));
Query OK, 0 rows affected (0.14 sec)

-- 通过Orders表的数据,将测试数据初始化到Orders_MV表中
mysql> insert into Orders_MV
-> select product_name, sum(price),
-> sum(amount), avg(price), count(*)
-> from Orders
-> group by product_name;
Query OK, 2 rows affected (0.07 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> select * from Orders_MV;
+--------------+-----------+------------+-----------+------------+
| product_name | price_sum | amount_sum | price_avg | orders_cnt |
+--------------+-----------+------------+-----------+------------+
| cpu | 366.40 | 8 | 122.133 | 3 |
| memory | 48.20 | 3 | 48.2 | 1 |
+--------------+-----------+------------+-----------+------------+
2 rows in set (0.00 sec)

-- 在MySQL workbench中输入,比较方便
delimiter //

CREATE TRIGGER tgr_Orders_insert -- 创建触发器为tgr_Orders_insert
AFTER INSERT ON Orders -- 触发器是INSERT类型的,且作用于Orders表
FOR EACH ROW
BEGIN
SET @old_price_sum := 0; -- 设置临时存放Orders_MV表(模拟物化视图)的字段的变量
SET @old_amount_sum := 0;
SET @old_price_avg := 0;
SET @old_orders_cnt := 0;
SELECT -- select ... into ... 在更新Orders_MV之前,将Orders_MV中对应某个产品的信息写入临时变量
IFNULL(price_sum, 0),
IFNULL(amount_sum, 0),
IFNULL(price_avg, 0),
IFNULL(orders_cnt, 0)
FROM
Orders_MV
WHERE
product_name = NEW.product_name INTO @old_price_sum , @old_amount_sum , @old_price_avg , @old_orders_cnt;

SET @new_price_sum = @old_price_sum + NEW.price; -- 累加新的值
SET @new_amount_sum = @old_amount_sum + NEW.amount;
SET @new_orders_cnt = @old_orders_cnt + 1;
SET @new_price_avg = @new_price_sum / @new_orders_cnt ;

REPLACE INTO Orders_MV
VALUES(NEW.product_name, @new_price_sum,
@new_amount_sum, @new_price_avg, @new_orders_cnt );
-- REPLACE 将对应的物品(唯一索引)的字段值替换new_xxx的值
END;//

delimiter ;


mysql> insert into Orders values (null, 'ssd', 299, 3);
Query OK, 1 row affected (0.03 sec)

mysql> insert into Orders values (null, 'memory', 47.9, 5);
Query OK, 1 row affected (0.05 sec)

mysql> select * from Orders_MV;
+--------------+-----------+------------+-----------+------------+
| product_name | price_sum | amount_sum | price_avg | orders_cnt |
+--------------+-----------+------------+-----------+------------+
| cpu | 366.40 | 8 | 122.133 | 3 |
| memory | 96.10 | 8 | 48.05 | 2 | -- 数量自动增加了1,价格也发生了变化
| ssd | 299.00 | 3 | 299 | 1 | -- 新增加的ssd产品
+--------------+-----------+------------+-----------+------------+
3 rows in set (0.00 sec)


--
-- IFNULL MySQL内建函数的演示
--
mysql> select @test;
+-------+
| @test |
+-------+
| NULL | -- 当前会话中没有test变量
+-------+
1 row in set (0.00 sec)

mysql> select ifnull(@test, 100); -- 如果test为NULL,则ifnull返回100
+--------------------+
| ifnull(@test, 100) |
+--------------------+
| 100 | -- ifnull函数return的值是100
+--------------------+
1 row in set (0.00 sec)

mysql> select @test;
+-------+
| @test |
+-------+
| NULL | -- 但是test还是NULL
+-------+
1 row in set (0.00 sec)

mysql> set @test:=200; -- 给test变量赋值为200
Query OK, 0 rows affected (0.00 sec)

mysql> select ifnull(@test, 100); -- 再次ifnull判断,此时test不为null,则返回test变量的值
+--------------------+
| ifnull(@test, 100) |
+--------------------+
| 200 | -- test不为null。返回test的值200
+--------------------+
1 row in set (0.00 sec)

--
-- select into 用法
--
mysql> select @id_1;
+-------+
| @id_1 |
+-------+
| NULL | -- 当前变量id_1为null
+-------+
1 row in set (0.00 sec)

mysql> select @score_1;
+----------+
| @score_1 |
+----------+
| NULL | -- 当前变量score_1为null
+----------+
1 row in set (0.00 sec)

mysql> select * from test_rank_2;
+------+-------+
| id | score |
+------+-------+
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 30 |
| 5 | 40 |
| 6 | 40 |
+------+-------+
6 rows in set (0.00 sec)

mysql> select * from test_rank_2
-> where id=1 into @id_1, @score_1;
-- 选择id=1的记录,将对应的id和score赋值给变量 id_1 和 score_1
Query OK, 1 row affected (0.00 sec)

mysql> select @id_1;
+-------+
| @id_1 |
+-------+
| 1 |
+-------+
1 row in set (0.00 sec)

mysql> select @score_1;
+----------+
| @score_1 |
+----------+
| 10 |
+----------+
1 row in set (0.00 sec)

-- 触发器对性能会有影响,相当于在一个事物中插入了其他的事物

三. 存储过程

1. 存储过程介绍

  • 存储在数据库端的一组SQL语句集;
  • 用户可以通过存储过程名和传参多次调用的程序模块;
  • 存储过程的特点:
    • 使用灵活,可以使用流控语句、自定义变量等完成复杂的业务逻辑;
    • 提高数据安全性,屏蔽应用程序直接对表的操作,易于进行审计;
    • 减少网络传输;
    • 提高代码维护的复杂度,实际使用需要结合业务评估;
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CREATE
[DEFINER = { user | CURRENT_USER }]
PROCEDURE sp_name ([proc_parameter[,...]])
[characteristic ...] routine_body


proc_parameter: -- 注意,只有procedure才有in(传入),out(传出),inout(传入传出)参数,自定义函数(只有)默认就是 in。
[ IN | OUT | INOUT ] param_name type


characteristic:
COMMENT 'string'
| LANGUAGE SQL
| [NOT] DETERMINISTIC
| { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
| SQL SECURITY { DEFINER | INVOKER }

routine_body:
Valid SQL routine statement


-- 删除
DROP PROCEDURE procedure_name;

2. 存储过程举例与流程控制语句

流程控制语句 官方文档

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--
-- IF
--
-- 语法
IF search_condition THEN statement_list
[ELSEIF search_condition THEN statement_list] ...
[ELSE statement_list]
END IF

-- 例子
mysql> delimiter //
mysql> create procedure pcd_test_1 (in param_a int) -- 创建一个
-> begin
-> declare a int; -- delcare声明了该变量的作用域在该procedure中
-> if param_a > 10 then set a:=11;
-> elseif param_a = 10 then set a:=10;
-> else set a:=9;
-> end if;
-> end;//
Query OK, 0 rows affected (0.01 sec)

mysql> select @a; -- 查看当前会话中变量a的值
+------+
| @a |
+------+
| NULL | -- 当前会话中a为NULL
+------+
1 row in set (0.00 sec)

mysql> call pcd_test_1(1);
+------+
| a |
+------+
| 9 |
+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> call pcd_test_1(10);
+------+
| a |
+------+
| 10 |
+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> call pcd_test_1(20);
+------+
| a |
+------+
| 11 |
+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> select @a;
+------+
| @a |
+------+
| NULL | -- 使用了declare,使得procedure中a的作用域限制在了procedure内
+------+
1 row in set (0.00 sec)

--
-- CASE WHEN
--
-- CASE WHEN 语法
CASE case_value
WHEN when_value THEN statement_list
[WHEN when_value THEN statement_list] ...
[ELSE statement_list]
END CASE
-- 或者是
CASE
WHEN search_condition THEN statement_list
[WHEN search_condition THEN statement_list] ...
[ELSE statement_list]
END CASE

--
-- CASE WHEN 例子
--
mysql> delimiter //
mysql>
mysql> create procedure pcd_test_2(in param_1 int)
-> begin
-> case param_1
-- 当case后面有value时,该value会和when中的when_value进行"="判断
-- 相等则执行then后面的语句,然后跳出;否则就进行下一次when的匹配
-> when 2 then select 200;
-> when 3 then select 300;
-> else
-> begin
-- 当没有匹配时,且else中没有要执行的语句
-- 则给一个begin/end的空语句;
-- 或者不写else语句;
-> end;
-> end case;
-> end;//
Query OK, 0 rows affected (0.03 sec)

mysql> delimiter ;
mysql> call pcd_test_2(1);
Query OK, 0 rows affected (0.00 sec)

mysql> call pcd_test_2(2);
+-----+
| 200 |
+-----+
| 200 |
+-----+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> call pcd_test_2(3);
+-----+
| 300 |
+-----+
| 300 |
+-----+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

-- 另外一种SQL语法请参考rank排名作业;注意when后跟的是condition

--
-- WHILE 循环
--
-- WHILE 语法
[begin_label:] WHILE search_condition DO
statement_list
END WHILE [end_label]

-- WHILE举例
mysql> delimiter //
mysql>
mysql> create procedure pcd_test_3(in param_1 int)
-> begin
-> declare a int default 1;
-> while param_1 > 10 do
-> set param_1 = param_1 - 1;
-> set a = a + 1;
-> end while;
-> select a;
-> end;//

Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ;

mysql> call pcd_test_3(15); -- 15 - 10 = 5;需要5次循环
+------+
| a |
+------+
| 6 | -- a + 5 = 6
+------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)


--
-- REPEAT 循环
--
-- REPEAT 语法
[begin_label:] REPEAT
statement_list
UNTIL search_condition
END REPEAT [end_label]

mysql> delimiter //
mysql> create procedure pcd_test_4(in param_1 int)
-> begin
-> SET @x = 0; -- 没有使用declare,所以x是会话级别的
-> REPEAT
-> SET @x = @x + 1;
-> UNTIL @x > param_1 END REPEAT;
-> end;//
Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ;

mysql> call pcd_test_4(10);
Query OK, 0 rows affected (0.00 sec)

mysql> select @x; -- x是会话级别的
+------+
| @x |
+------+
| 11 | -- 一共循环11次(10>10 为False,11 > 10为True,才跳出)
+------+
1 row in set (0.00 sec)

--
-- loop 循环
--
-- loop语法
[begin_label:] LOOP
statement_list
END LOOP [end_label]

-- ITERATE 和label相结合,表示继续从label处执行
-- LEAVE 和label相结合,表示从label 标记的代码段离开

-- loop 例子
mysql> delimiter //
mysql> create procedure pcd_test_5(in param_1 int)
-> begin
-> test_label: loop
-> set param_1 := param_1 + 1; -- 参数累加
-> if param_1 < 10 then -- 如果累加的值小于10
-> iterate test_label; -- 继续执行 标签 test_label
-> end if;
-> leave test_label; -- 如果>=10则离开这个test_label(loop)
-> end loop test_label;
-> set @x = param_1; -- 设置会话级别的变量
-> end;//

Query OK, 0 rows affected (0.02 sec)
mysql> delimiter ;

mysql> call pcd_test_5(5); -- 5<10 ,累加5次后>=10为true,离开循环
Query OK, 0 rows affected (0.00 sec)

mysql> select @x;
+------+
| @x |
+------+
| 10 | -- 累加到10的 param_1 赋值给 x, 即为10
+------+
1 row in set (0.00 sec)


-- 老师给出的例子, 阶乘
mysql> create table test_proc_1(a int, b int); -- 给一个存放数据的表
Query OK, 0 rows affected (0.15 sec)

mysql> delimiter //
mysql> create procedure proc_test1(in total int, out res int)
-> begin
-> declare i int;
-> set i := 1;
-> set res := 1;
-> if total <= 0 then
-> set total := 1;
-> end if;
-> while i <= total do
-> set res := res * i;
-> insert into test_proc_1 values(i, res);
-> set i := i + 1;
-> end while;
-> end;//
Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ;

mysql> set @res_value := 0;
Query OK, 0 rows affected (0.00 sec)

mysql> call proc_test1(5, @res_value); -- 因为res是out变量,要预先有这个变量,这里上面设置了res_value(实参和形参不必同名)
Query OK, 1 row affected (0.15 sec)

mysql> select @res_value;
+------------+
| @res_value |
+------------+
| 120 | -- 5的阶乘的结果是120
+------------+
1 row in set (0.00 sec)

mysql> select * from test_proc_1;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 | -- 每次insert的结果
+------+------+
5 rows in set (0.00 sec)

三. 自定义函数

  • 自定义函数和存储过程很类似,但是必须要有返回值;
  • 与内置的函数(sum(), max()等)使用方法类似
    • select fun(val);
    • select * from t where col= fun(val);
  • 自定义函数可能在遍历每条记录中使用;
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CREATE
[DEFINER = { user | CURRENT_USER }]
FUNCTION sp_name ([func_parameter[,...]])
RETURNS type -- 必须有返回值
[characteristic ...] routine_body

func_parameter:
param_name type

type:
Any valid MySQL data type

characteristic:
COMMENT 'string'
| LANGUAGE SQL
| [NOT] DETERMINISTIC
| { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
| SQL SECURITY { DEFINER | INVOKER }

routine_body:
Valid SQL routine statement

-- 删除
DROP FUNCTION fun_name;
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-- 老师给的例子,还是阶乘,用自定义函数的方式

mysql> delimiter //
mysql>
mysql> create function fun_test_1(total int)
-> returns int
-> begin
-> declare i int;
-> declare res int;
-> set i := 1;
-> set res := 1;
-> if total <= 0 then
-> set total := 1;
-> end if;
-> while i <= total do
-> set res := res * i;
-> set i := i + 1;
-> end while;
-> return res;
-> end;//
ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)
-- 报错,提示因为函的声明中没有"DETERMINISTIC, NO SQL, or READS SQL DATA"等关键字 ,需要使用打开参数 log_bin_trust_function_creators

-- 解决方法,set global log_bin_trust_function_creators=1; 开启该选项可能会引起主从服务器不一致
-- 或者 增加 上述相应功能的关键字


-- 使用 deterministic 关键字
-- 当你声明一个函数的返回是确定性的,则必须显示的使用deterministic关键字,默认是 no deterministic的
mysql> delimiter //
mysql> create function fun_test_1(total int)
-> returns int deterministic -- 这个只是告诉MySQL我这个函数是否会改变数据
-- 即使我下面使用了insert,update等DML语句,MySQL不会检查
-- 函数是否会改变数据,完全依赖创建函数的用户去指定的关键字
-- 而非真的是否有修改数据
-- 只是声明,而非约束
-> begin
-> declare i int;
-> declare res int;
-> set i := 1;
-> set res := 1;
-> if total <= 0 then
-> set total := 1;
-> end if;
-> while i <= total do
-> set res := res * i;
-> insert into test_proc_1 values(i, res); -- 在自定义函数中,同样可以使用sql
-- 并且该SQL是insert,其实和deterministic违背。
-> set i := i + 1;
-> end while;
-> return res;
-> end;//
Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ;

mysql> truncate table test_proc_1;
Query OK, 0 rows affected (0.11 sec)

mysql> select fun_test_1(6); -- return了6的阶乘,720
+---------------+
| fun_test_1(6) |
+---------------+
| 720 |
+---------------+
1 row in set (0.02 sec)

mysql> select * from test_proc_1;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 | -- 使用了insert语句进行插入阶乘的历史记录
+------+------+
6 rows in set (0.00 sec)

-- 关键字简单说明
-- DETERMINISTIC : 当给定相同的输入,产生确定的结果
-- NOT DETERMINISTIC : 默认值,认为产生的结果是不确定的

-- READS SQL DATA : 只是读取SQL数据
-- MODIFIES SQL DATA : 会修改数据
-- NO SQL : 没有SQL遇见
-- CONTAINS SQL : 包含SQL语句,但是没有读写语句,理论有select now()等

原文链接
部分原文:
By default, for a CREATE FUNCTION statement to be accepted, at least one of DETERMINISTIC, NO SQL, or READS SQL DATA must be specified explicitly. Otherwise an error occurs:
默认情况下,在创建自定义函数时,必须显示的指定关键字DETERMINISTIC, NO SQL, 或者是 READS SQL DATA中的至少一个(可以多个),否则就会有如下错误

ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL,or READS SQL DATA in its declaration and binary logging is enabled (you might want to use the less safe log_bin_trust_function_creators
variable)

网上参考资料1
网上参考资料2

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