MySQL | 尚硅谷 | 第16章_变量、流程控制与游标 - ToB企服应用市场:ToB评测及商务社交产业平台

#查看所有全局变量
SHOW GLOBAL VARIABLES;
#查看所有会话变量
SHOW SESSION VARIABLES;
#或
SHOW VARIABLES;
#查看满足条件的部分系统变量。
SHOW GLOBAL VARIABLES LIKE '%标识符%';
#查看满足条件的部分会话变量
SHOW SESSION VARIABLES LIKE '%标识符%';
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SHOW GLOBAL VARIABLES LIKE 'admin_%';
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#查看指定的系统变量的值
SELECT @@global.变量名;
#查看指定的会话变量的值
SELECT @@session.变量名;
#或者
SELECT @@变量名;
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#为某个系统变量赋值
#方式1：
SET @@global.变量名=变量值;
#方式2：
SET GLOBAL 变量名=变量值;
#为某个会话变量赋值
#方式1：
SET @@session.变量名=变量值;
#方式2：
SET SESSION 变量名=变量值;
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SELECT @@global.autocommit;
SET GLOBAL autocommit=0;
SELECT @@session.tx_isolation;
SET @@session.tx_isolation='read-uncommitted';
SET GLOBAL max_connections = 1000;
SELECT @@global.max_connections;
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SELECT @用户变量 := 表达式 [FROM 等子句];
SELECT 表达式 INTO @用户变量 [FROM 等子句];
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SELECT @用户变量
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SET @a = 1;
SELECT @a;
SELECT @num := COUNT(*) FROM employees;
SELECT @num;
SELECT AVG(salary) INTO @avgsalary FROM employees;
SELECT @avgsalary;
SELECT @big;
#查看某个未声明的变量时，将得到NULL值
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BEGIN
#声明局部变量
DECLARE 变量名1 变量数据类型 [DEFAULT 变量默认值];
DECLARE 变量名2,变量名3,... 变量数据类型 [DEFAULT 变量默认值];
#为局部变量赋值
SET 变量名1 = 值;
SELECT 值 INTO 变量名2 [FROM 子句];
#查看局部变量的值
SELECT 变量1,变量2,变量3;
END
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1.定义变量
DECLARE 变量名类型 [default 值];
# 如果没有DEFAULT子句，初始值为NULL
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DECLARE myparam INT DEFAULT 100;
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2.变量赋值

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SET 变量名=值;
SET 变量名:=值;
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SELECT 字段名或表达式 INTO 变量名 FROM 表;
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**3.使用变量（查看、比较、运算等）**
SELECT 局部变量名;
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DELIMITER //
CREATE PROCEDURE set_value()
BEGIN
DECLARE emp_name VARCHAR(25);
DECLARE sal DOUBLE(10,2);
SELECT last_name,salary INTO emp_name,sal
FROM employees
WHERE employee_id = 102;
SELECT emp_name,sal;
END //
DELIMITER ;
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#方式1：使用用户变量
SET @m=1;
SET @n=1;
SET @sum=@m+@n;
SELECT @sum;
#方式2：使用局部变量
DELIMITER //
CREATE PROCEDURE add_value()
BEGIN
#局部变量
DECLARE m INT DEFAULT 1;
DECLARE n INT DEFAULT 3;
DECLARE SUM INT;
SET SUM = m+n;
SELECT SUM;
END //
DELIMITER ;
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#声明
DELIMITER //
CREATE PROCEDURE different_salary(IN emp_id INT,OUT dif_salary DOUBLE)
BEGIN
#声明局部变量
DECLARE emp_sal,mgr_sal DOUBLE DEFAULT 0.0;
DECLARE mgr_id INT;
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT manager_id INTO mgr_id FROM employees WHERE employee_id = emp_id;
SELECT salary INTO mgr_sal FROM employees WHERE employee_id = mgr_id;
SET dif_salary = mgr_sal - emp_sal;
END //
DELIMITER ;
#调用
SET @emp_id = 102;
CALL different_salary(@emp_id,@diff_sal);
#查看
SELECT @diff_sal;
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#1. 变量
#1.1 变量：系统变量（全局系统变量、会话系统变量） vs 用户自定义变量
#1.2 查看系统变量
#查询全局系统变量
SHOW GLOBAL VARIABLES; #617
#查询会话系统变量
SHOW SESSION VARIABLES; #640
SHOW VARIABLES; #默认查询的是会话系统变量
#查询部分系统变量
SHOW GLOBAL VARIABLES LIKE 'admin_%';
SHOW VARIABLES LIKE 'character_%';
#1.3 查看指定系统变量
SELECT @@global.max_connections;
SELECT @@global.character_set_client;
#错误：
SELECT @@global.pseudo_thread_id;
#错误：
SELECT @@session.max_connections;
SELECT @@session.character_set_client;
SELECT @@session.pseudo_thread_id;
SELECT @@character_set_client; #先查询会话系统变量，再查询全局系统变量
#1.4 修改系统变量的值
#全局系统变量：
#方式1：
SET @@global.max_connections = 161;
#方式2：
SET GLOBAL max_connections = 171;
#针对于当前的数据库实例是有效的，一旦重启mysql服务，就失效了。
#会话系统变量：
#方式1：
SET @@session.character_set_client = 'gbk';
#方式2：
SET SESSION character_set_client = 'gbk';
#针对于当前会话是有效的，一旦结束会话，重新建立起新的会话，就失效了。
#1.5 用户变量
/*
① 用户变量：会话用户变量 vs 局部变量
② 会话用户变量：使用"@"开头，作用域为当前会话。
③ 局部变量：只能使用在存储过程和存储函数中的。
*/
#1.6 会话用户变量
/*
① 变量的声明和赋值：
#方式1：“=”或“:=”
SET @用户变量 = 值;
SET @用户变量 := 值;
#方式2：“:=” 或 INTO关键字
SELECT @用户变量 := 表达式 [FROM 等子句];
SELECT 表达式 INTO @用户变量 [FROM 等子句];
② 使用
SELECT @变量名
*/
#准备工作
CREATE DATABASE dbtest16;
USE dbtest16;
CREATE TABLE employees
AS
SELECT * FROM atguigudb.`employees`;
CREATE TABLE departments
AS
SELECT * FROM atguigudb.`departments`;
SELECT * FROM employees;
SELECT * FROM departments;
#测试：
#方式1：
SET @m1 = 1;
SET @m2 := 2;
SET @sum := @m1 + @m2;
SELECT @sum;
/*输出
+------+
| @sum |
+------+
| 3 |
+------+
*/
#方式2：
SELECT @count := COUNT(*) FROM employees;
/*
+--------------------+
| @count := COUNT(*) |
+--------------------+
| 107 |
+--------------------+
*/
SELECT @count;
/*输出
+--------+
| @count |
+--------+
| 107 |
+--------+
*/
SELECT AVG(salary) INTO @avg_sal FROM employees;
SELECT @avg_sal;
/*
+-------------------+
| @avg_sal |
+-------------------+
| 6461.682242990654 |
+-------------------
*/
#1.7 局部变量
/*
1、局部变量必须满足：
① 使用DECLARE声明
② 声明并使用在BEGIN ... END 中（使用在存储过程、函数中）
③ DECLARE的方式声明的局部变量必须声明在BEGIN中的首行的位置。
2、声明格式：
DECLARE 变量名类型 [default 值]; # 如果没有DEFAULT子句，初始值为NULL
3、赋值：
方式1：
SET 变量名=值;
SET 变量名:=值;
方式2：
SELECT 字段名或表达式 INTO 变量名 FROM 表;
4、使用
SELECT 局部变量名;
*/
#举例：
DELIMITER //
CREATE PROCEDURE test_var()
BEGIN
#1、声明局部变量
DECLARE a INT DEFAULT 0;
DECLARE b INT ;
#DECLARE a,b INT DEFAULT 0;
DECLARE emp_name VARCHAR(25);
#2、赋值
SET a = 1;
SET b := 2;
SELECT last_name INTO emp_name FROM employees WHERE employee_id = 101;
#3、使用
SELECT a,b,emp_name;
END //
DELIMITER ;
#调用存储过程
CALL test_var();
/*输出：
+------+------+----------+
| a | b | emp_name |
+------+------+----------+
| 1 | 2 | Kochhar |
+------+------+----------+
*/
#举例1：声明局部变量，并分别赋值为employees表中employee_id为102的last_name和salary
DELIMITER //
CREATE PROCEDURE test_pro()
BEGIN
#声明
DECLARE emp_name VARCHAR(25);
DECLARE sal DOUBLE(10,2) DEFAULT 0.0;
#赋值
SELECT last_name,salary INTO emp_name,sal
FROM employees
WHERE employee_id = 102;
#使用
SELECT emp_name,sal;
END //
DELIMITER ;
#调用存储过程
CALL test_pro();
/*
+----------+----------+
| emp_name | sal |
+----------+----------+
| De Haan | 17000.00 |
+----------+----------+
*/
SELECT last_name,salary FROM employees
WHERE employee_id = 102;
#举例2：声明两个变量，求和并打印（分别使用会话用户变量、局部变量的方式实现）
#方式1：使用会话用户变量
SET @v1 = 10;
SET @v2 := 20;
SET @result := @v1 + @v2;
#查看
SELECT @result;
#方式2：使用局部变量
DELIMITER //
CREATE PROCEDURE add_value()
BEGIN
#声明
DECLARE value1,value2,sum_val INT;
#赋值
SET value1 = 10;
SET value2 := 100;
SET sum_val = value1 + value2;
#使用
SELECT sum_val;
END //
DELIMITER ;
#调用存储过程
CALL add_value();
/*
+---------+
| sum_val |
+---------+
| 110 |
+---------+
*/
#举例3：创建存储过程“different_salary”查询某员工和他领导的薪资差距，并用IN参数emp_id接收员工id，
#用OUT参数dif_salary输出薪资差距结果。
DELIMITER //
CREATE PROCEDURE different_salary(IN emp_id INT,OUT dif_salary DOUBLE)
BEGIN
#分析：查询出emp_id员工的工资;查询出emp_id员工的管理者的id;查询管理者id的工资;计算两个工资的差值
#声明变量
DECLARE emp_sal DOUBLE DEFAULT 0.0; #记录员工的工资
DECLARE mgr_sal DOUBLE DEFAULT 0.0; #记录管理者的工资
DECLARE mgr_id INT DEFAULT 0; #记录管理者的id
#赋值
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT manager_id INTO mgr_id FROM employees WHERE employee_id = emp_id;
SELECT salary INTO mgr_sal FROM employees WHERE employee_id = mgr_id;
SET dif_salary = mgr_sal - emp_sal;
END //
DELIMITER ;
#调用存储过程
SET @emp_id := 103;
SET @dif_sal := 0;
CALL different_salary(@emp_id,@dif_sal);
SELECT @dif_sal;
/*
+----------+
| @dif_sal |
+----------+
| 8000 |
+----------+
*/
SELECT * FROM employees;
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DELIMITER //
CREATE PROCEDURE UpdateDataNoCondition()
BEGIN
SET @x = 1;
UPDATE employees SET email = NULL WHERE last_name = 'Abel';
SET @x = 2;
UPDATE employees SET email = 'aabbel' WHERE last_name = 'Abel';
SET @x = 3;
END //
DELIMITER ;

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CALL UpdateDataNoCondition();
#ERROR 1048 (23000): Column 'email' cannot be null
SELECT @x;
/*
+------+
| @x |
+------+
| 1 |
+------+*/

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DECLARE 错误名称 CONDITION FOR 错误码（或错误条件）
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DECLARE Field_Not_Be_NULL CONDITION FOR 1048;
#使用sqlstate_value
DECLARE Field_Not_Be_NULL CONDITION FOR SQLSTATE '23000';
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#使用MySQL_error_code
DECLARE command_not_allowed CONDITION FOR 1148;
#使用sqlstate_value
DECLARE command_not_allowed CONDITION FOR SQLSTATE '42000';
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DECLARE 处理方式 HANDLER FOR 错误类型处理语句
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**处理方式：处理方式有3个取值：CONTINUE、EXIT、UNDO**

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**错误类型（即条件）可以有如下取值:**

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#方法1：捕获sqlstate_value
DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02' SET @info = 'NO_SUCH_TABLE';
#方法2：捕获mysql_error_value
DECLARE CONTINUE HANDLER FOR 1146 SET @info = 'NO_SUCH_TABLE';
#方法3：先定义条件，再调用
DECLARE no_such_table CONDITION FOR 1146;
DECLARE CONTINUE HANDLER FOR NO_SUCH_TABLE SET @info = 'NO_SUCH_TABLE';
#方法4：使用SQLWARNING
DECLARE EXIT HANDLER FOR SQLWARNING SET @info = 'ERROR';
#方法5：使用NOT FOUND
DECLARE EXIT HANDLER FOR NOT FOUND SET @info = 'NO_SUCH_TABLE';
#方法6：使用SQLEXCEPTION
DECLARE EXIT HANDLER FOR SQLEXCEPTION SET @info = 'ERROR';
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DELIMITER //
CREATE PROCEDURE UpdateDataNoCondition()
BEGIN
#定义处理程序
DECLARE CONTINUE HANDLER FOR 1048 SET @proc_value = -1;
SET @x = 1;
UPDATE employees SET email = NULL WHERE last_name = 'Abel';
SET @x = 2;
UPDATE employees SET email = 'aabbel' WHERE last_name = 'Abel';
SET @x = 3;
END //
DELIMITER ;
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CALL UpdateDataWithCondition();
#Query OK, 0 rows affected (0.01 sec)
SELECT @x,@proc_value;
/*
+ ------ +------------- +
| @x | @proc_value |
+ ------ +------------- +
| 3 | -1 |
+ ------ +------------- +*/
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#准备工作
CREATE TABLE departments
AS
SELECT * FROM atguigudb.`departments`;
ALTER TABLE departments
ADD CONSTRAINT uk_dept_name UNIQUE(department_id);
DELIMITER //
CREATE PROCEDURE InsertDataWithCondition()
BEGIN
DECLARE duplicate_entry CONDITION FOR SQLSTATE '23000' ;
DECLARE EXIT HANDLER FOR duplicate_entry SET @proc_value = -1;
SET @x = 1;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 2;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 3;
END //
DELIMITER ;
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CALL InsertDataWithCondition();
#Query OK, 0 rows affected (0.01 sec)
SELECT @x,@proc_value;
/*
+ ------ +------------- +
| @x | @proc_value |
+ ------ +------------- +
| 2 | -1 |
+ ------ +------------- +
*/
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#2. 定义条件和处理程序
#2.1 错误演示：
#错误代码： 1364
#Field 'email' doesn't have a default value
INSERT INTO employees(last_name)
VALUES('Tom');
DESC employees;
#错误演示：
DELIMITER //
CREATE PROCEDURE UpdateDataNoCondition()
BEGIN
SET @x = 1;
UPDATE employees SET email = NULL WHERE last_name = 'Abel';
SET @x = 2;
UPDATE employees SET email = 'aabbel' WHERE last_name = 'Abel';
SET @x = 3;
END //
DELIMITER ;
#调用存储过程
#错误代码： 1048
#Column 'email' cannot be null
CALL UpdateDataNoCondition();#ERROR 1048 (23000): Column 'email' cannot be null
SELECT @x;
#输出：@x = 1处出现错误
/*
+------+
| @x |
+------+
| 1 |
+------+
*/
#2.2 定义条件
#格式：DECLARE 错误名称 CONDITION FOR 错误码（或错误条件）
#举例1：定义“Field_Not_Be_NULL”错误名与MySQL中违反非空约束的错误类型
#是“ERROR 1048 (23000)”对应。
#方式1：使用MySQL_error_code
DECLARE Field_Not_Be_NULL CONDITION FOR 1048;
#方式2：使用sqlstate_value
DECLARE Field_Not_Be_NULL CONDITION FOR SQLSTATE '23000';
#举例2：定义"ERROR 1148(42000)"错误，名称为command_not_allowed。
#方式1：使用MySQL_error_code
DECLARE command_not_allowed CONDITION FOR 1148;
#方式2：使用sqlstate_value
DECLARE command_not_allowed CONDITION FOR SQLSTATE '42000';
#2.3 定义处理程序
#格式：DECLARE 处理方式 HANDLER FOR 错误类型处理语句
#举例：
#方法1：捕获sqlstate_value
DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02' SET @info = 'NO_SUCH_TABLE';
#方法2：捕获mysql_error_value
DECLARE CONTINUE HANDLER FOR 1146 SET @info = 'NO_SUCH_TABLE';
#方法3：先定义条件，再调用
DECLARE no_such_table CONDITION FOR 1146;
DECLARE CONTINUE HANDLER FOR no_such_table SET @info = 'NO_SUCH_TABLE';
#方法4：使用SQLWARNING
DECLARE EXIT HANDLER FOR SQLWARNING SET @info = 'ERROR';
#方法5：使用NOT FOUND
DECLARE EXIT HANDLER FOR NOT FOUND SET @info = 'NO_SUCH_TABLE';
#方法6：使用SQLEXCEPTION
DECLARE EXIT HANDLER FOR SQLEXCEPTION SET @info = 'ERROR';
#2.4 案例的处理
DROP PROCEDURE UpdateDataNoCondition;
#重新定义存储过程，体现错误的处理程序
DELIMITER //
CREATE PROCEDURE UpdateDataNoCondition()
BEGIN
#声明处理程序
#处理方式1：
DECLARE CONTINUE HANDLER FOR 1048 SET @prc_value = -1;
#处理方式2：
#DECLARE CONTINUE HANDLER FOR sqlstate '23000' SET @prc_value = -1;
SET @x = 1;
UPDATE employees SET email = NULL WHERE last_name = 'Abel';
SET @x = 2;
UPDATE employees SET email = 'aabbel' WHERE last_name = 'Abel';
SET @x = 3;
END //
DELIMITER ;
#调用存储过程：
CALL UpdateDataNoCondition();
#查看变量：
SELECT @x,@prc_value;
#2.5 再举一个例子：
#创建一个名称为“InsertDataWithCondition”的存储过程
#① 准备工作
CREATE TABLE departments
AS
SELECT * FROM atguigudb.`departments`;
DESC departments;
ALTER TABLE departments
ADD CONSTRAINT uk_dept_name UNIQUE(department_id);
#② 定义存储过程：
DELIMITER //
CREATE PROCEDURE InsertDataWithCondition()
BEGIN
SET @x = 1;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 2;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 3;
END //
DELIMITER ;
#③ 调用
CALL InsertDataWithCondition();
SELECT @x; #2
#④ 删除此存储过程
DROP PROCEDURE IF EXISTS InsertDataWithCondition;
#⑤ 重新定义存储过程（考虑到错误的处理程序）
DELIMITER //
CREATE PROCEDURE InsertDataWithCondition()
BEGIN
#处理程序
#方式1：
#declare exit handler for 1062 set @pro_value = -1;
#方式2：
#declare exit handler for sqlstate '23000' set @pro_value = -1;
#方式3：
#定义条件
DECLARE duplicate_entry CONDITION FOR 1062;
DECLARE EXIT HANDLER FOR duplicate_entry SET @pro_value = -1;
SET @x = 1;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 2;
INSERT INTO departments(department_name) VALUES('测试');
SET @x = 3;
END //
DELIMITER ;
#调用
CALL InsertDataWithCondition();
SELECT @x,@pro_value;
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IF 表达式1 THEN 操作1
[ELSEIF 表达式2 THEN 操作2]……
[ELSE 操作N]
END IF

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IF val IS NULL
THEN SELECT 'val is null';
ELSE SELECT 'val is not null';
END IF;

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DELIMITER //
CREATE PROCEDURE update_salary_by_eid1(IN emp_id INT)
BEGIN
DECLARE emp_salary DOUBLE;
DECLARE hire_year DOUBLE;
SELECT salary INTO emp_salary FROM employees WHERE employee_id = emp_id;
SELECT DATEDIFF(CURDATE(),hire_date)/365 INTO hire_year FROM employees WHERE employee_id = emp_id;
IF emp_salary < 8000 AND hire_year > 5
THEN UPDATE employees SET salary = salary + 500 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;

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DELIMITER //
CREATE PROCEDURE update_salary_by_eid2(IN emp_id INT)
BEGIN
DECLARE emp_salary DOUBLE;
DECLARE hire_year DOUBLE;
SELECT salary INTO emp_salary FROM employees WHERE employee_id = emp_id;
SELECT DATEDIFF(CURDATE(),hire_date)/365 INTO hire_year FROM employees WHERE employee_id = emp_id;
IF emp_salary < 8000 AND hire_year > 5
THEN UPDATE employees SET salary = salary + 500 WHERE employee_id =emp_id;
ELSE
UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;

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DELIMITER //
CREATE PROCEDURE update_salary_by_eid3(IN emp_id INT)
BEGIN
DECLARE emp_salary DOUBLE;
DECLARE bonus DECIMAL(3,2);
SELECT salary INTO emp_salary FROM employees WHERE employee_id = emp_id; SELECT commission_pct INTO bonus FROM employees WHERE employee_id = emp_id;
IF emp_salary < 9000
THEN UPDATE employees SET salary = 9000 WHERE employee_id = emp_id;
ELSEIF emp_salary < 10000 AND bonus IS NULL
THEN UPDATE employees SET commission_pct = 0.01 WHERE employee_id =emp_id;
ELSE
UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;
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#情况一：类似于switch
CASE 表达式
WHEN 值1 THEN 结果1或语句1(如果是语句，需要加分号)
WHEN 值2 THEN 结果2或语句2(如果是语句，需要加分号)
...
ELSE 结果n或语句n(如果是语句，需要加分号)
END [case]（如果是放在begin end中需要加上case，如果放在select后面不需要）
CASE 语句的语法结构2：
#情况二：类似于多重if
CASE
WHEN 条件1 THEN 结果1或语句1(如果是语句，需要加分号)
WHEN 条件2 THEN 结果2或语句2(如果是语句，需要加分号)
...
ELSE 结果n或语句n(如果是语句，需要加分号)
END [case]（如果是放在begin end中需要加上case，如果放在select后面不需要）
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CASE val
WHEN 1 THEN SELECT 'val is 1';
WHEN 2 THEN SELECT 'val is 2';
ELSE SELECT 'val is not 1 or 2';
END CASE;
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CASE
WHEN val IS NULL THEN SELECT 'val is null';
WHEN val < 0 THEN SELECT 'val is less than 0';
WHEN val > 0 THEN SELECT 'val is greater than 0';
ELSE SELECT 'val is 0';
END CASE;
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DELIMITER //
CREATE PROCEDURE update_salary_by_eid4(IN emp_id INT)
BEGIN
DECLARE emp_sal DOUBLE;
DECLARE bonus DECIMAL(3,2);
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT commission_pct INTO bonus FROM employees WHERE employee_id = emp_id;
CASE
WHEN emp_sal<9000
THEN UPDATE employees SET salary=9000 WHERE employee_id = emp_id;
WHEN emp_sal<10000 AND bonus IS NULL
THEN UPDATE employees SET commission_pct=0.01 WHERE employee_id = emp_id;
ELSE
UPDATE employees SET salary=salary+100 WHERE employee_id = emp_id;
END CASE;
END //
DELIMITER ;
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DELIMITER //
CREATE PROCEDURE update_salary_by_eid5(IN emp_id INT)
BEGIN
DECLARE emp_sal DOUBLE;
DECLARE hire_year DOUBLE;
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT ROUND(DATEDIFF(CURDATE(),hire_date)/365) INTO hire_year FROM employees WHERE employee_id = emp_id;
CASE hire_year
WHEN 0 THEN UPDATE employees SET salary=salary+50 WHERE employee_id = emp_id;
WHEN 1 THEN UPDATE employees SET salary=salary+100 WHERE employee_id = emp_id;
WHEN 2 THEN UPDATE employees SET salary=salary+200 WHERE employee_id = emp_id;
WHEN 3 THEN UPDATE employees SET salary=salary+300 WHERE employee_id = emp_id;
WHEN 4 THEN UPDATE employees SET salary=salary+400 WHERE employee_id = emp_id;
ELSE UPDATE employees SET salary=salary+500 WHERE employee_id = emp_id;
END CASE;
END //
DELIMITER ;
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[loop_label:] LOOP
循环执行的语句
END LOOP [loop_label]
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DECLARE id INT DEFAULT 0;
add_loop:LOOP
SET id = id +1;
IF id >= 10 THEN LEAVE add_loop;
END IF;
END LOOP add_loop;
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DELIMITER //
CREATE PROCEDURE update_salary_loop(OUT num INT)
BEGIN
DECLARE avg_salary DOUBLE;
DECLARE loop_count INT DEFAULT 0;
SELECT AVG(salary) INTO avg_salary FROM employees;
label_loop:LOOP
IF avg_salary >= 12000 THEN LEAVE label_loop;
END IF;
UPDATE employees SET salary = salary * 1.1;
SET loop_count = loop_count + 1;
SELECT AVG(salary) INTO avg_salary FROM employees;
END LOOP label_loop;
SET num = loop_count;
END //
DELIMITER ;
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[while_label:] WHILE 循环条件 DO
循环体
END WHILE [while_label];
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DELIMITER //
CREATE PROCEDURE test_while()
BEGIN
DECLARE i INT DEFAULT 0;
WHILE i < 10 DO
SET i = i + 1;
END WHILE;
SELECT i;
END //
DELIMITER ;
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#调用
CALL test_while();
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DELIMITER //
CREATE PROCEDURE update_salary_while(OUT num INT)
BEGIN
DECLARE avg_sal DOUBLE ;
DECLARE while_count INT DEFAULT 0;
SELECT AVG(salary) INTO avg_sal FROM employees;
WHILE avg_sal > 5000 DO
UPDATE employees SET salary = salary * 0.9;
SET while_count = while_count + 1;
SELECT AVG(salary) INTO avg_sal FROM employees; END WHILE;
SET num = while_count;
END //
DELIMITER ;
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[repeat_label:] REPEAT
循环体的语句
UNTIL 结束循环的条件表达式
END REPEAT [repeat_label]
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DELIMITER //
CREATE PROCEDURE test_repeat()
BEGIN
DECLARE i INT DEFAULT 0;
REPEAT
SET i = i + 1;
UNTIL i >= 10
END REPEAT;
SELECT i;
END //
DELIMITER ;
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DELIMITER //
CREATE PROCEDURE update_salary_repeat(OUT num INT)
BEGIN
DECLARE avg_sal DOUBLE ;
DECLARE repeat_count INT DEFAULT 0;
SELECT AVG(salary) INTO avg_sal FROM employees;
REPEAT
UPDATE employees SET salary = salary * 1.15;
SET repeat_count = repeat_count + 1;
SELECT AVG(salary) INTO avg_sal FROM employees;
UNTIL avg_sal >= 13000
END REPEAT;
SET num = repeat_count;
END //
DELIMITER ;
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LEAVE 标记名
1

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DELIMITER //
CREATE PROCEDURE leave_begin(IN num INT)
begin_label: BEGIN
IF num<=0
THEN LEAVE begin_label;
ELSEIF num=1
THEN SELECT AVG(salary) FROM employees;
ELSEIF num=2
THEN SELECT MIN(salary) FROM employees;
ELSE
SELECT MAX(salary) FROM employees;
END IF;
SELECT COUNT(*) FROM employees;
END //
DELIMITER ;
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DELIMITER //
CREATE PROCEDURE leave_while(OUT num INT)
BEGIN
#
DECLARE avg_sal DOUBLE;#记录平均工资
DECLARE while_count INT DEFAULT 0; #记录循环次数
SELECT AVG(salary) INTO avg_sal FROM employees; #① 初始化条件
while_label:WHILE TRUE DO #② 循环条件
#③ 循环体
IF avg_sal <= 10000 THEN
LEAVE while_label;
END IF;
UPDATE employees SET salary = salary * 0.9;
SET while_count = while_count + 1;
#④ 迭代条件
SELECT AVG(salary) INTO avg_sal FROM employees;
END WHILE;
#赋值
SET num = while_count;
END //
DELIMITER ;
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ITERATE label
1

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DELIMITER //
CREATE PROCEDURE test_iterate()
BEGIN
DECLARE num INT DEFAULT 0;
my_loop:LOOP
SET num = num + 1;
IF num < 10
THEN ITERATE my_loop;
ELSEIF num > 15
THEN LEAVE my_loop;
END IF;
SELECT '尚硅谷：让天下没有难学的技术';
END LOOP my_loop;
END //
DELIMITER ;
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#3. 流程控制
#3.1 分支结构之 IF
#举例1
DELIMITER //
CREATE PROCEDURE test_if()
BEGIN
#情况1：
#声明局部变量
#declare stu_name varchar(15);
#if stu_name is null
# then select 'stu_name is null';
#end if;
#情况2：二选一
#declare email varchar(25) default 'aaa';
#if email is null
# then select 'email is null';
#else
# select 'email is not null';
#end if;
#情况3：多选一
DECLARE age INT DEFAULT 20;
IF age > 40
THEN SELECT '中老年';
ELSEIF age > 18
THEN SELECT '青壮年';
ELSEIF age > 8
THEN SELECT '青少年';
ELSE
SELECT '婴幼儿';
END IF;
END //
DELIMITER ;
#调用
CALL test_if();
DROP PROCEDURE test_if;
#举例2：声明存储过程“update_salary_by_eid1”，定义IN参数emp_id，输入员工编号。
#判断该员工薪资如果低于8000元并且入职时间超过5年，就涨薪500元；否则就不变。
DELIMITER //
CREATE PROCEDURE update_salary_by_eid1(IN emp_id INT)
BEGIN
#声明局部变量
DECLARE emp_sal DOUBLE; #记录员工的工资
DECLARE hire_year DOUBLE; #记录员工入职公司的年头
#赋值
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT DATEDIFF(CURDATE(),hire_date)/365 INTO hire_year FROM employees WHERE employee_id = emp_id;
#判断
IF emp_sal < 8000 AND hire_year >= 5
THEN UPDATE employees SET salary = salary + 500 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;
#调用存储过程
CALL update_salary_by_eid1(104);
SELECT DATEDIFF(CURDATE(),hire_date)/365, employee_id,salary
FROM employees
WHERE salary < 8000 AND DATEDIFF(CURDATE(),hire_date)/365 >= 5;
DROP PROCEDURE update_salary_by_eid1;
#举例3：声明存储过程“update_salary_by_eid2”，定义IN参数emp_id，输入员工编号。
#判断该员工薪资如果低于9000元并且入职时间超过5年，就涨薪500元；否则就涨薪100元。
DELIMITER //
CREATE PROCEDURE update_salary_by_eid2(IN emp_id INT)
BEGIN
#声明局部变量
DECLARE emp_sal DOUBLE; #记录员工的工资
DECLARE hire_year DOUBLE; #记录员工入职公司的年头
#赋值
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT DATEDIFF(CURDATE(),hire_date)/365 INTO hire_year FROM employees WHERE employee_id = emp_id;
#判断
IF emp_sal < 9000 AND hire_year >= 5
THEN UPDATE employees SET salary = salary + 500 WHERE employee_id = emp_id;
ELSE
UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;
#调用
CALL update_salary_by_eid2(103);
CALL update_salary_by_eid2(104);
SELECT * FROM employees
WHERE employee_id IN (103,104);
#举例4：声明存储过程“update_salary_by_eid3”，定义IN参数emp_id，输入员工编号。
#判断该员工薪资如果低于9000元，就更新薪资为9000元；薪资如果大于等于9000元且
#低于10000的，但是奖金比例为NULL的，就更新奖金比例为0.01；其他的涨薪100元。
DELIMITER //
CREATE PROCEDURE update_salary_by_eid3(IN emp_id INT)
BEGIN
#声明变量
DECLARE emp_sal DOUBLE; #记录员工工资
DECLARE bonus DOUBLE; #记录员工的奖金率
#赋值
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT commission_pct INTO bonus FROM employees WHERE employee_id = emp_id;
#判断
IF emp_sal < 9000
THEN UPDATE employees SET salary = 9000 WHERE employee_id = emp_id;
ELSEIF emp_sal < 10000 AND bonus IS NULL
THEN UPDATE employees SET commission_pct = 0.01 WHERE employee_id = emp_id;
ELSE
UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
END IF;
END //
DELIMITER ;
#调用
CALL update_salary_by_eid3(102);
CALL update_salary_by_eid3(103);
CALL update_salary_by_eid3(104);
SELECT *
FROM employees
WHERE employee_id IN (102,103,104);
##3.2 分支结构之case
#举例1:基本使用
DELIMITER //
CREATE PROCEDURE test_case()
BEGIN
#演示1：case ... when ...then ...
/*
declare var int default 2;
case var
when 1 then select 'var = 1';
when 2 then select 'var = 2';
when 3 then select 'var = 3';
else select 'other value';
end case;
*/
#演示2：case when ... then ....
DECLARE var1 INT DEFAULT 10;
CASE
WHEN var1 >= 100 THEN SELECT '三位数';
WHEN var1 >= 10 THEN SELECT '两位数';
ELSE SELECT '个数位';
END CASE;
END //
DELIMITER ;
#调用
CALL test_case();
DROP PROCEDURE test_case;
#举例2：声明存储过程“update_salary_by_eid4”，定义IN参数emp_id，输入员工编号。
#判断该员工薪资如果低于9000元，就更新薪资为9000元；薪资大于等于9000元且低于10000的，
#但是奖金比例为NULL的，就更新奖金比例为0.01；其他的涨薪100元。
DELIMITER //
CREATE PROCEDURE update_salary_by_eid4(IN emp_id INT)
BEGIN
#局部变量的声明
DECLARE emp_sal DOUBLE; #记录员工的工资
DECLARE bonus DOUBLE; #记录员工的奖金率
#局部变量的赋值
SELECT salary INTO emp_sal FROM employees WHERE employee_id = emp_id;
SELECT commission_pct INTO bonus FROM employees WHERE employee_id = emp_id;
CASE
WHEN emp_sal < 9000 THEN UPDATE employees SET salary = 9000 WHERE employee_id = emp_id;
WHEN emp_sal < 10000 AND bonus IS NULL THEN UPDATE employees SET commission_pct = 0.01
WHERE employee_id = emp_id;
ELSE UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
END CASE;
END //
DELIMITER ;
#调用
CALL update_salary_by_eid4(103);
CALL update_salary_by_eid4(104);
CALL update_salary_by_eid4(105);
SELECT *
FROM employees
WHERE employee_id IN (103,104,105);
#举例3：声明存储过程update_salary_by_eid5，定义IN参数emp_id，输入员工编号。
#判断该员工的入职年限，如果是0年，薪资涨50；如果是1年，薪资涨100；
#如果是2年，薪资涨200；如果是3年，薪资涨300；如果是4年，薪资涨400；其他的涨薪500。
DELIMITER //
CREATE PROCEDURE update_salary_by_eid5(IN emp_id INT)
BEGIN
#声明局部变量
DECLARE hire_year INT; #记录员工入职公司的总时间（单位：年）
#赋值
SELECT ROUND(DATEDIFF(CURDATE(),hire_date) / 365) INTO hire_year
FROM employees WHERE employee_id = emp_id;
#判断
CASE hire_year
WHEN 0 THEN UPDATE employees SET salary = salary + 50 WHERE employee_id = emp_id;
WHEN 1 THEN UPDATE employees SET salary = salary + 100 WHERE employee_id = emp_id;
WHEN 2 THEN UPDATE employees SET salary = salary + 200 WHERE employee_id = emp_id;
WHEN 3 THEN UPDATE employees SET salary = salary + 300 WHERE employee_id = emp_id;
WHEN 4 THEN UPDATE employees SET salary = salary + 400 WHERE employee_id = emp_id;
ELSE UPDATE employees SET salary = salary + 500 WHERE employee_id = emp_id;
END CASE;
END //
DELIMITER ;
#调用
CALL update_salary_by_eid5(101);
SELECT *
FROM employees
DROP PROCEDURE update_salary_by_eid5;
#4.1 循环结构之LOOP
/*
[loop_label:] LOOP
循环执行的语句
END LOOP [loop_label]
*/
#举例1：
DELIMITER //
CREATE PROCEDURE test_loop()
BEGIN
#声明局部变量
DECLARE num INT DEFAULT 1;
loop_label:LOOP
#重新赋值
SET num = num + 1;
#可以考虑某个代码程序反复执行。（略）
IF num >= 10 THEN LEAVE loop_label;
END IF;
END LOOP loop_label;
#查看num
SELECT num;
END //
DELIMITER ;
#调用
CALL test_loop();
/*
+------+
| num |
+------+
| 10 |
+------+
*/
#举例2：当市场环境变好时，公司为了奖励大家，决定给大家涨工资。
#声明存储过程“update_salary_loop()”，声明OUT参数num，输出循环次数。
#存储过程中实现循环给大家涨薪，薪资涨为原来的1.1倍。直到全公司的平
#均薪资达到12000结束。并统计循环次数。
DELIMITER //
CREATE PROCEDURE update_salary_loop(OUT num INT)
BEGIN
#声明变量
DECLARE avg_sal DOUBLE ; #记录员工的平均工资
DECLARE loop_count INT DEFAULT 0;#记录循环的次数
#① 初始化条件
#获取员工的平均工资
SELECT AVG(salary) INTO avg_sal FROM employees;
loop_lab:LOOP
#② 循环条件
#结束循环的条件
IF avg_sal >= 12000
THEN LEAVE loop_lab;
END IF;
#③ 循环体
#如果低于12000，更新员工的工资
UPDATE employees SET salary = salary * 1.1;
#④ 迭代条件
#更新avg_sal变量的值
SELECT AVG(salary) INTO avg_sal FROM employees;
#记录循环次数
SET loop_count = loop_count + 1;
END LOOP loop_lab;
#给num赋值
SET num = loop_count;
END //
DELIMITER ;
SELECT AVG(salary) FROM employees;
CALL update_salary_loop(@num);
SELECT @num;
#4.2 循环结构之WHILE
/*
[while_label:] WHILE 循环条件 DO
循环体
END WHILE [while_label];
*/
#举例1：
DELIMITER //
CREATE PROCEDURE test_while()
BEGIN
#初始化条件
DECLARE num INT DEFAULT 1;
#循环条件
WHILE num <= 10 DO
#循环体（略）
#迭代条件
SET num = num + 1;
END WHILE;
#查询
SELECT num;
END //
DELIMITER ;
#调用
CALL test_while();
/*输出
+------+
| num |
+------+
| 11 |
+------+
*/
#举例2：市场环境不好时，公司为了渡过难关，决定暂时降低大家的薪资。
#声明存储过程“update_salary_while()”，声明OUT参数num，输出循环次数。
#存储过程中实现循环给大家降薪，薪资降为原来的90%。直到全公司的平均薪资
#达到5000结束。并统计循环次数。
DELIMITER //
CREATE PROCEDURE update_salary_while(OUT num INT)
BEGIN
#声明变量
DECLARE avg_sal DOUBLE ; #记录平均工资
DECLARE while_count INT DEFAULT 0; #记录循环次数
#赋值
SELECT AVG(salary) INTO avg_sal FROM employees;
WHILE avg_sal > 5000 DO
UPDATE employees SET salary = salary * 0.9 ;
SET while_count = while_count + 1;
SELECT AVG(salary) INTO avg_sal FROM employees;
END WHILE;
#给num赋值
SET num = while_count;
END //
DELIMITER ;
#调用
CALL update_salary_while(@num);
SELECT @num;
SELECT AVG(salary) FROM employees;
#4.3 循环结构之REPEAT
/*
[repeat_label:] REPEAT
　　　　循环体的语句
UNTIL 结束循环的条件表达式
END REPEAT [repeat_label]
*/
#举例1：
DELIMITER //
CREATE PROCEDURE test_repeat()
BEGIN
#声明变量
DECLARE num INT DEFAULT 1;
REPEAT
SET num = num + 1;
UNTIL num >= 10
END REPEAT;
#查看
SELECT num;
END //
DELIMITER ;
#调用
CALL test_repeat();
#举例2：当市场环境变好时，公司为了奖励大家，决定给大家涨工资。
#声明存储过程“update_salary_repeat()”，声明OUT参数num，输出循环次数。
#存储过程中实现循环给大家涨薪，薪资涨为原来的1.15倍。直到全公司的平均
#薪资达到13000结束。并统计循环次数。
DELIMITER //
CREATE PROCEDURE update_salary_repeat(OUT num INT)
BEGIN
#声明变量
DECLARE avg_sal DOUBLE ; #记录平均工资
DECLARE repeat_count INT DEFAULT 0; #记录循环次数
#赋值
SELECT AVG(salary) INTO avg_sal FROM employees;
REPEAT
UPDATE employees SET salary = salary * 1.15;
SET repeat_count = repeat_count + 1;
SELECT AVG(salary) INTO avg_sal FROM employees;
UNTIL avg_sal >= 13000
END REPEAT;
#给num赋值
SET num = repeat_count;
END //
DELIMITER ;
#调用
CALL update_salary_repeat(@num);
SELECT @num;
SELECT AVG(salary) FROM employees;
/*
凡是循环结构，一定具备4个要素：
1. 初始化条件
2. 循环条件
3. 循环体
4. 迭代条件
*/
#5.1 LEAVE的使用
/*
**举例1：**创建存储过程 “leave_begin()”，声明INT类型的IN参数num。给BEGIN...END加标记名，
并在BEGIN...END中使用IF语句判断num参数的值。
- 如果num<=0，则使用LEAVE语句退出BEGIN...END；
- 如果num=1，则查询“employees”表的平均薪资；
- 如果num=2，则查询“employees”表的最低薪资；
- 如果num>2，则查询“employees”表的最高薪资。
IF语句结束后查询“employees”表的总人数。
*/
DELIMITER //
CREATE PROCEDURE leave_begin(IN num INT)
begin_label:BEGIN
IF num <= 0
THEN LEAVE begin_label;
ELSEIF num = 1
THEN SELECT AVG(salary) FROM employees;
ELSEIF num = 2
THEN SELECT MIN(salary) FROM employees;
ELSE
SELECT MAX(salary) FROM employees;
END IF;
#查询总人数
SELECT COUNT(*) FROM employees;
END //
DELIMITER ;
#调用
CALL leave_begin(1);
#举例2：当市场环境不好时，公司为了渡过难关，决定暂时降低大家的薪资。
#声明存储过程“leave_while()”，声明OUT参数num，输出循环次数，存储过程中使用WHILE
#循环给大家降低薪资为原来薪资的90%，直到全公司的平均薪资小于等于10000，并统计循环次数。
DELIMITER //
CREATE PROCEDURE leave_while(OUT num INT)
BEGIN
#
DECLARE avg_sal DOUBLE;#记录平均工资
DECLARE while_count INT DEFAULT 0; #记录循环次数
SELECT AVG(salary) INTO avg_sal FROM employees; #① 初始化条件
while_label:WHILE TRUE DO #② 循环条件
#③ 循环体
IF avg_sal <= 10000 THEN
LEAVE while_label;
END IF;
UPDATE employees SET salary = salary * 0.9;
SET while_count = while_count + 1;
#④ 迭代条件
SELECT AVG(salary) INTO avg_sal FROM employees;
END WHILE;
#赋值
SET num = while_count;
END //
DELIMITER ;
#调用
CALL leave_while(@num);
SELECT @num;
SELECT AVG(salary) FROM employees;
#5.2 ITERATE的使用
/*
举例：定义局部变量num，初始值为0。循环结构中执行num + 1操作。
- 如果num < 10，则继续执行循环；
- 如果num > 15，则退出循环结构；
*/
DELIMITER //
CREATE PROCEDURE test_iterate()
BEGIN
DECLARE num INT DEFAULT 0;
loop_label:LOOP
#赋值
SET num = num + 1;
IF num < 10
THEN ITERATE loop_label;
ELSEIF num > 15
THEN LEAVE loop_label;
END IF;
SELECT '让天下没有难学的技术';
END LOOP;
END //
DELIMITER ;
CALL test_iterate();
/*
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
1 row in set (0.00 sec)
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
1 row in set (0.00 sec)
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
1 row in set (0.01 sec)
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
1 row in set (0.01 sec)
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
1 row in set (0.02 sec)
+------------------------+
| ：让天下没有难学的技术 |
+------------------------+
| 让天下没有难学的技术 |
+------------------------+
*/
SELECT * FROM employees;
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SELECT employee_id,last_name,salary FROM employees WHERE salary > 15000;

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DECLARE cursor_name CURSOR FOR select_statement;

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DECLARE cursor_name CURSOR IS select_statement;

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DECLARE cur_emp CURSOR FOR
SELECT employee_id,salary FROM employees;
DECLARE cursor_fruit CURSOR FOR
SELECT f_name, f_price FROM fruits ;

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OPEN cursor_name

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OPEN cur_emp ;

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FETCH cursor_name INTO var_name [, var_name] ...

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FETCH cur_emp INTO emp_id, emp_sal ;

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CLOSE cursor_name

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CLOSE cur_emp;

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DELIMITER //
CREATE PROCEDURE get_count_by_limit_total_salary(IN limit_total_salary DOUBLE,OUT total_count INT)
BEGIN
DECLARE sum_salary DOUBLE DEFAULT 0;
#记录累加的总工资
DECLARE cursor_salary DOUBLE DEFAULT 0;
#记录某一个工资值
DECLARE emp_count INT DEFAULT 0;
#记录循环个数
#定义游标
DECLARE emp_cursor CURSOR FOR SELECT salary FROM employees ORDER BY salary DESC;
#打开游标
OPEN emp_cursor;
REPEAT
#使用游标（从游标中获取数据）
FETCH emp_cursor INTO cursor_salary;
SET sum_salary = sum_salary + cursor_salary;
SET emp_count = emp_count + 1;
UNTIL sum_salary >= limit_total_salary
END REPEAT;
SET total_count = emp_count;
#关闭游标
CLOSE emp_cursor;
END //
DELIMITER ;

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SET GLOBAL MAX_EXECUTION_TIME=2000;
1

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SET PERSIST global max_connections = 1000;
1

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show variables like '%max_connections%';
/*
+ ------------------------ + ------- +
| Variable_name | Value |
+ ------------------------ + ------- +
| max_connections | 151 |
| mysqlx_max_connections | 100 |
+ ------------------------ + ------- +*/

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set persist max_connections=1000;
#Query OK, 0 rows affected (0.00 sec)

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show variables like '%max_connections%';
/*+ ------------------------ + ------- +
| Variable_name | Value |
+ ------------------------ + ------- +
| max_connections | 1000 |
| mysqlx_max_connections | 100 |
+ ------------------------ + ------- +*/

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#6. 游标的使用
/*
游标使用的步骤：
① 声明游标
② 打开游标
③ 使用游标（从游标中获取数据）
④ 关闭游标
*/
#举例：创建存储过程“get_count_by_limit_total_salary()”，声明IN参数 limit_total_salary，
#DOUBLE类型；声明OUT参数total_count，INT类型。函数的功能可以实现累加薪资最高的几个员工的薪资值，
#直到薪资总和达到limit_total_salary参数的值，返回累加的人数给total_count。
DELIMITER //
CREATE PROCEDURE get_count_by_limit_total_salary(IN limit_total_salary DOUBLE,OUT total_count INT)
BEGIN
#声明局部变量
DECLARE sum_sal DOUBLE DEFAULT 0.0; #记录累加的工资总额
DECLARE emp_sal DOUBLE; #记录每一个员工的工资
DECLARE emp_count INT DEFAULT 0;#记录累加的人数
#1.声明游标
DECLARE emp_cursor CURSOR FOR SELECT salary FROM employees ORDER BY salary DESC;
#2.打开游标
OPEN emp_cursor;
REPEAT
#3.使用游标
FETCH emp_cursor INTO emp_sal;
SET sum_sal = sum_sal + emp_sal;
SET emp_count = emp_count + 1;
UNTIL sum_sal >= limit_total_salary
END REPEAT;
SET total_count = emp_count;
#4.关闭游标
CLOSE emp_cursor;
END //
DELIMITER ;
#调用
CALL get_count_by_limit_total_salary(200000,@total_count);
SELECT @total_count;
/*输出：
+--------------+
| @total_count |
+--------------+
| 15 |
+--------------+
*/

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#第16章_变量、流程控制与游标的课后练习
/*
变量：
系统变量（全局系统变量、会话系统变量）
用户自定义变量（会话用户变量、局部变量）
*/
#练习1：测试变量的使用
#存储函数的练习
#0. 准备工作
CREATE DATABASE test16_var_cursor;
USE test16_var_cursor;
CREATE TABLE employees
AS
SELECT * FROM atguigudb.`employees`;
CREATE TABLE departments
AS
SELECT * FROM atguigudb.`departments`;
SET GLOBAL log_bin_trust_function_creators = 1;
#无参有返回
#1. 创建函数get_count(),返回公司的员工个数
DELIMITER $
CREATE FUNCTION get_count()
RETURNS INT
BEGIN
#声明局部变量
DECLARE emp_count INT;
#赋值
SELECT COUNT(*) INTO emp_count FROM employees;
RETURN emp_count;
END $
DELIMITER ;
#调用
SELECT get_count();
/*输出：
+-------------+
| get_count() |
+-------------+
| 107 |
+-------------+
*/
#有参有返回
#2. 创建函数ename_salary(),根据员工姓名，返回它的工资
DELIMITER $
CREATE FUNCTION ename_salary(emp_name VARCHAR(15))
RETURNS DOUBLE
BEGIN
#声明变量
SET @sal = 0; #定义了一个会话用户变量
#赋值
SELECT salary INTO @sal FROM employees WHERE last_name = emp_name;
RETURN @sal;
END $
DELIMITER ;
#调用
SELECT ename_salary('Abel');
/*
+----------------------+
| ename_salary('Abel') |
+----------------------+
| 11000 |
+----------------------+
*/
SELECT @sal;
/*
+-------+
| @sal |
+-------+
| 11000 |
+-------+
*/
#3. 创建函数dept_sal() ,根据部门名，返回该部门的平均工资
DELIMITER //
CREATE FUNCTION dept_sal(dept_name VARCHAR(15))
RETURNS DOUBLE
BEGIN
DECLARE avg_sal DOUBLE;
SELECT AVG(salary) INTO avg_sal
FROM employees e JOIN departments d
ON e.department_id = d.department_id
WHERE d.department_name = dept_name;
RETURN avg_sal;
END //
DELIMITER ;
#调用
SELECT * FROM departments;
SELECT dept_sal('Marketing');
/*
+-----------------------+
| dept_sal('Marketing') |
+-----------------------+
| 9500 |
+-----------------------+
*/
#4. 创建函数add_float()，实现传入两个float，返回二者之和
DELIMITER //
CREATE FUNCTION add_float(value1 FLOAT,value2 FLOAT)
RETURNS FLOAT
BEGIN
DECLARE sum_val FLOAT ;
SET sum_val = value1 + value2;
RETURN sum_val;
END //
DELIMITER ;
# 调用
SET @v1 := 12.2;
SET @v2 = 2.3;
SELECT add_float(@v1,@v2);
/*
+--------------------+
| add_float(@v1,@v2) |
+--------------------+
| 14.5 |
+--------------------+
*/
#2. 流程控制
/*
分支：if \ case ... when \ case when ...
循环：loop \ while \ repeat
其它：leave \ iterate
*/
#1. 创建函数test_if_case()，实现传入成绩，如果成绩>90,返回A，如果成绩>80,返回B，如果成绩>60,返回C，否则返回D
#要求：分别使用if结构和case结构实现
#方式1：if
DELIMITER $
CREATE FUNCTION test_if_case1(score DOUBLE)
RETURNS CHAR
BEGIN
#声明变量
DECLARE score_level CHAR;
IF score > 90
THEN SET score_level = 'A';
ELSEIF score > 80
THEN SET score_level = 'B';
ELSEIF score > 60
THEN SET score_level = 'C';
ELSE
SET score_level = 'D';
END IF;
#返回
RETURN score_level;
END $
DELIMITER ;
#调用
SELECT test_if_case1(56);
#方式2：case when ...
DELIMITER $
CREATE FUNCTION test_if_case2(score DOUBLE)
RETURNS CHAR
BEGIN
#声明变量
DECLARE score_level CHAR;
CASE
WHEN score > 90 THEN SET score_level = 'A';
WHEN score > 80 THEN SET score_level = 'B';
WHEN score > 60 THEN SET score_level = 'C';
ELSE SET score_level = 'D';
END CASE;
#返回
RETURN score_level;
END $
DELIMITER ;
#调用
SELECT test_if_case2(76);
#2. 创建存储过程test_if_pro()，传入工资值，如果工资值<3000,则删除工资为此值的员工，
# 如果3000 <= 工资值 <= 5000,则修改此工资值的员工薪资涨1000，否则涨工资500
DELIMITER $
CREATE PROCEDURE test_if_pro(IN sal DOUBLE)
BEGIN
IF sal < 3000
THEN DELETE FROM employees WHERE salary = sal;
ELSEIF sal <= 5000
THEN UPDATE employees SET salary = salary + 1000 WHERE salary = sal;
ELSE
UPDATE employees SET salary = salary + 500 WHERE salary = sal;
END IF;
END $
DELIMITER ;
#调用
CALL test_if_pro(24000);
SELECT * FROM employees;
#3. 创建存储过程insert_data(),传入参数为 IN 的 INT 类型变量 insert_count,实现向admin表中
#批量插入insert_count条记录
CREATE TABLE admin(
id INT PRIMARY KEY AUTO_INCREMENT,
user_name VARCHAR(25) NOT NULL,
user_pwd VARCHAR(35) NOT NULL
);
SELECT * FROM admin;
DELIMITER $
CREATE PROCEDURE insert_data(IN insert_count INT)
BEGIN
#声明变量
DECLARE init_count INT DEFAULT 1; #①初始化条件
WHILE init_count <= insert_count DO #② 循环条件
#③ 循环体
INSERT INTO admin(user_name,user_pwd) VALUES (CONCAT('atguigu-',init_count),ROUND(RAND()*1000000));
#④ 迭代条件
SET init_count = init_count + 1;
END WHILE;
END $
DELIMITER ;
#调用
CALL insert_data(100);
#3. 游标的使用
#创建存储过程update_salary()，参数1为 IN 的INT型变量dept_id，表示部门id；
#参数2为 IN的INT型变量change_sal_count，表示要调整薪资的员工个数。查询指定id部门的员工信息，
#按照salary升序排列，根据hire_date的情况，调整前change_sal_count个员工的薪资，详情如下。
DELIMITER $
CREATE PROCEDURE update_salary(IN dept_id INT,IN change_sal_count INT)
BEGIN
#声明变量
DECLARE emp_id INT ;#记录员工id
DECLARE emp_hire_date DATE; #记录员工入职时间
DECLARE init_count INT DEFAULT 1; #用于表示循环结构的初始化条件
DECLARE add_sal_rate DOUBLE ; #记录涨薪的比例
#声明游标
DECLARE emp_cursor CURSOR FOR SELECT employee_id,hire_date FROM employees
WHERE department_id = dept_id ORDER BY salary ASC;
#打开游标
OPEN emp_cursor;
WHILE init_count <= change_sal_count DO
#使用游标
FETCH emp_cursor INTO emp_id,emp_hire_date;
#获取涨薪的比例
IF (YEAR(emp_hire_date) < 1995)
THEN SET add_sal_rate = 1.2;
ELSEIF(YEAR(emp_hire_date) <= 1998)
THEN SET add_sal_rate = 1.15;
ELSEIF(YEAR(emp_hire_date) <= 2001)
THEN SET add_sal_rate = 1.10;
ELSE
SET add_sal_rate = 1.05;
END IF;
#涨薪操作
UPDATE employees SET salary = salary * add_sal_rate
WHERE employee_id = emp_id;
#迭代条件的更新
SET init_count = init_count + 1;
END WHILE;
#关闭游标
CLOSE emp_cursor;
END $
DELIMITER ;
#调用
CALL update_salary(50,3);
SELECT employee_id,hire_date,salary
FROM employees
WHERE department_id = 50
ORDER BY salary ASC;

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