知识点四:MySQL流程控制语句(7-10)
选择语句:
(IF ELSE ELSE IF CASE 分支)IFNULL函数
IF语法:
语法规则:
IF search_condition THEN statmen_list ;
[SLSEIF search_condition THEN statmen_list];
ELSE statmen_list;
END IF;
--7 流程控制语句之选择语句
DELIMITER //
CREATE PROCEDURE p_test7(IN age INT)
BEGIN
IF age >=18 THEN SELECT '成年人';
ELSE SELECT '未成年人';
END IF;
END
// DELIMITER ;
SET @age =4;
CALL p_test7(@age); SELECT @age; DELIMITER //
CREATE PROCEDURE p_test8(IN age INT)
BEGIN
IF age >=18 AND age < 60 THEN SELECT '成年人';
ELSEIF age >= 60 THEN SELECT '老年人';
ELSE SELECT '未成年人';
END IF;
END
// DELIMITER ;
SET @age =60;
CALL p_test8(@age); SELECT @age;
IF语句测试
CASE语法
CASE语句也用来进行条件判断,其可以实现比IF语句更复杂的条件判断。
CASE语法的基本形势如下:
CASE case_value
WHEN when_value THEN
statement_list;
[WHEN when_value THEN
statement_list];…;
[ELSE statement_list];
END CASE;
--8 流程控制语句之选择语句CASE分支 --默认数据(创建工资表)
CREATE DATABASE mzjj;
USE mzjj; CREATE TABLE salaries(
emp_no INT KEY NOT NULL AUTO_INCREMENT,
salary INT,
from_data DATE DEFAULT '2015-04-01',
to_data DATE DEFAULT '2015-05-01'
)AUTO_INCREMENT=1001; DELIMITER //
CREATE PROCEDURE p_addsalary(IN v_empno INT)
BEGIN
DECLARE addS int;
CASE v_empno
WHEN 1001 THEN SET addS = 1500;
WHEN 1002 THEN SET addS = 2500;
WHEN 1003 THEN SET addS = 3500;
ELSE SET adds =1000;
END CASE;
UPDATE salaries SET salary = addS WHERE emp_no= v_empno;
END
// DELIMITER ;
SET @v_empno =1001;
CALL p_addsalary(@v_empno); SELECT @v_empno; --默认数据(创建员工信息表)
CREATE TABLE employees(
emp_no INT KEY NOT NULL AUTO_INCREMENT,
birth_data DATE DEFAULT '2015-04-01',
first_name VARCHAR(20),
last_name VARCHAR(20),
gender ENUM('M','F'),
hire_data DATE DEFAULT '2015-05-01'
)AUTO_INCREMENT=1001; SELECT emp_no,first_name,last_name,
(CASE gender WHEN 'M' THEN '男'ELSE '女' END) AS '性别' FROM employees;
CASE语句测试
IFNULL函数:
用法:
IFNULL(exp1,exp2)
如果exp1是NULL则返回exp2;否则返回exp1;
示例:
SELECT IFNULL(null,'不是空');
SELECT IFNULL(123,'不是空');
--测试IFNULL函数
UPDATE employees SET first_name=NULL WHERE emp_no =1001;
SELECT IFNULL(first_name,'无名字') FROM employees;
IFNULL函数测试
循环语句:
WHILE语句:
语法规则:
WHILE 条件 DO
内容
END WHILE;
--9 流程控制(WHILE循环语句)
--计算1加到100
DELIMITER //
CREATE PROCEDURE p_addnum()
BEGIN
DECLARE i int DEFAULT 1;
DECLARE addresult int DEFAULT 0;
WHILE i<= 100 DO
SET addresult = addresult +i;
SET i = i+1;
END WHILE;
SELECT addresult;
END
// DELIMITER ;
CALL p_addnum(); --向表中加入1000条数据
DELIMITER //
CREATE PROCEDURE p_insertEmp()
BEGIN
DECLARE maxempno int DEFAULT 0;
DECLARE i int DEFAULT 1;
WHILE i<= 1000 DO
SELECT MAX(emp_no) into maxempno FROM employees;
SET maxempno = maxempno+1;
INSERT INTO employees(emp_no,birth_data, first_name,last_name, gender,hire_data)
VALUES(maxempno,'1990-1-1','jim','ju','M','2000-1-1');
SET i =i+1;
END WHILE;
END
// DELIMITER ;
CALL p_insertEmp();
WHILE语句测试
--任务作业
--更新编号为偶数的gender字段为M DELIMITER //
CREATE PROCEDURE changeEmp()
BEGIN DECLARE maxempno int DEFAULT 0;
DECLARE sex VARCHAR(2) DEFAULT 'M';
DECLARE minempno int DEFAULT 1;
SELECT MAX(emp_no) into maxempno FROM employees;
SELECT MIN(emp_no) into minempno FROM employees;
WHILE minempno <= maxempno DO
CASE minempno%2
WHEN 0 THEN SET sex = 'M';
ELSE SET sex = 'M';
END CASE;
UPDATE employees SET gender = sex WHERE emp_no= minempno;
SET minempno =minempno+1 ;
END WHILE;
END
//
DELIMITER ;
CALL changeEmp(); SELECT * FROM employees; DELIMITER //
CREATE PROCEDURE changeEmp2()
BEGIN DECLARE maxempno int DEFAULT 0;
DECLARE minempno int DEFAULT 1;
SELECT MAX(emp_no) into maxempno FROM employees;
SELECT MIN(emp_no) into minempno FROM employees;
WHILE minempno <= maxempno DO
IF minempno%2=0 THEN UPDATE employees SET gender = 'F' WHERE emp_no= minempno;
END IF;
SET minempno =minempno+1 ;
END WHILE;
END
//
DELIMITER ;
CALL changeEmp2();
任务作业
REPEAT语句:
语法规则:
REPEAT
内容
UNTIL 条件 //推出循环的条件
END REPEAT;
--rapeat测试
DELIMITER //
CREATE PROCEDURE changeEmp1()
BEGIN DECLARE maxempno int DEFAULT 0;
DECLARE sex VARCHAR(2) DEFAULT 'M';
DECLARE minempno int DEFAULT 1;
SELECT MAX(emp_no) into maxempno FROM employees;
SELECT MIN(emp_no) into minempno FROM employees;
REPEAT
if minempno%2 =0 then update employees SET gender='F' WHERE emp_no = minempno;
END IF;
SET minempno = minempno+1;
UNTIL minempno>maxempno
END REPEAT;
END
//
DELIMITER ;
CALL changeEmp1();
REPEAT语句测试
LOOP语句:
语法规则:
LOOP名字:LOOP
内容
IF 条件 THEN
LEAVE LOOP名字;
END IF;
END LOOP;
--loop测试
DELIMITER //
CREATE PROCEDURE changeEmp3() BEGIN
DECLARE maxempno int DEFAULT 0;
DECLARE minempno int DEFAULT 1;
SELECT MAX(emp_no) into maxempno FROM employees;
SELECT MIN(emp_no) into minempno FROM employees; myloop:loop
if minempno%2 =1 then update employees SET hire_data='1900-12-11' WHERE emp_no = minempno;
END IF;
SET minempno = minempno+1;
IF minempno>maxempno THEN LEAVE myloop;
END IF;
END loop;
END
// DELIMITER ;
CALL changeEmp3();
LOOP语句测试