mysql_16_常用函数

 1 CREATE DATABASE db_test;
 2 USE db_test;
 3
 4 CREATE TABLE t_t(
 5 id int PRIMARY KEY NOT NULL auto_increment,
 6 birthday date
 7 )
 8
 9 INSERT INTO t_t VALUES(1,"1994-08-21");
10 INSERT INTO t_t VALUES(2,"1995-04-15");
11 SELECT * FROM t_t;
12
13 -- 第十章:mysql常用函数
14 -- 第一节:日期和时间函数
15 -- 1.CURDATE()返回当前日期;
16 -- 2.CURTIME()返回当前时间;
17 -- 3.MONTH(date)返回日期date中的月份,范围是:1~12;
18 SELECT CURDATE() AS 当前日期,CURTIME() AS 当前时间,MONTH(birthday) AS 生日月份 from t_t;
19
20 -- 第二节:字符串数据
21 -- 1.CHAR_LENGTH(str)计算字符串str的字符数;
22 -- 2.upper(str)把所有字母变成大写字母;
23 -- 3.LOWER(str)把所有字母变成小写字母;
24 alter table t_t add userName varchar(20) after birthday;
25 UPDATE t_t SET userName="CaoFang" WHERE id=1;
26 UPDATE t_t SET userName="NiMei" WHERE id=2;
27 SELECT * FROM t_t;
28
29 SELECT userName AS 原姓名,CHAR_LENGTH(userName) AS 姓名字符数,UPPER(userName) AS 大写姓名,LOWER(userName) AS 小写姓名 FROM t_t;
30
31 -- 第三节:数学函数
32 -- 1.ABS(X)求绝对值
33 -- 2.SQRT(X)求平方根
34 -- 3.MOD(N,M)求余
35 alter table t_t add num int after userName;
36 UPDATE t_t SET num=2 WHERE id=1;
37 UPDATE t_t SET num=-3 WHERE id=2;
38 SELECT * FROM t_t;
39
40 SELECT num,ABS(num) AS 绝对值,SQRT(num) AS 平方根,MOD((SELECT num FROM t_t WHERE id=1),(SELECT num FROM t_t WHERE id=2)) AS 余数 FROM t_t;
41
42 -- 第四节:加密函数
43 alter table t_t add password varchar(100) after num;
44 SELECT * FROM t_t;
45
46 -- 1.PASSWORD(str)一般对用户的密码加密        不可逆
47 INSERT INTO t_t VALUES (NULL,"2017-08-09","lisi",4,PASSWORD("1"));
48
49 -- 2.MD5(str)普通加密        不可逆
50 INSERT INTO t_t VALUES (NULL,"2017-08-09","lisi",4,MD5("1"));
51
52 -- 3.ENCODE(str,pass_str) 加密函数,结果是一个二进制数。必须使用BLOB类型的字段来保存它;
53 alter table t_t add pp BLOB after password;
54
55 INSERT INTO t_t VALUES (NULL,"2017-08-09","lisi",4,NULL,ENCODE("123","aa"));
56 -- 4.DECODE(crypt_str,pass_str)解密函数;
57 SELECT pp FROM t_t WHERE id=5;
58
59 SELECT DECODE(pp,"aa") FROM t_t WHERE id=5;