文章目录
- 运算符
- 算术运算符
- 比较运算符
- 逻辑运算符
- MySQL运算符
- 数字函数
- 字符串函数
- 日期时间函数
- 条件函数
- 系统信息函数
- 加密函数
- 其他常用函数
- MySQL索引
- 索引的概念
- 索引的分类
- 创建索引
- 创建表时创建索引
- 在已经存在的表上创建索引
- 删除索引
- MySQL图形化管理工具
- PHPMyAdmin
- SQLyog
运算符
算术运算符
（1）加、减、乘、除
mysql> SELECT 1+1,1-1,2*4,3/8;
+-----+-----+-----+--------+
| 1+1 | 1-1 | 2*4 | 3/8 |
+-----+-----+-----+--------+
| 2 | 0 | 8 | 0.3750 |
+-----+-----+-----+--------+
1 row in set (0.09 sec)2）被除数是0时返回NULL
mysql> SELECT 3/0;
+------+
| 3/0 |
+------+
| NULL |
+------+
1 row in set (0.00 sec)mysql> SELECT 4 DIV 2;
+---------+
| 4 DIV 2 |
+---------+
| 2 |
+---------+
1 row in set (0.00 sec)（3）取余数
mysql> SELECT 3%8;
+------+
| 3%8 |
+------+
| 3 |
+------+
1 row in set (0.00 sec)mysql> SELECT 3 MOD 8;
+---------+
| 3 MOD 8 |
+---------+
| 3 |
+---------+
1 row in set (0.00 sec)（4） SQL的字符串转换功能
mysql> SELECT 1+'3MAIZI';
+------------+
| 1+'3MAIZI' |
+------------+
| 4 |
+------------+
1 row in set, 1 warning (0.03 sec)（5）和NULL进行算数运算结果仍未NULL
mysql> SELECT 1+NULL;
+--------+
| 1+NULL |
+--------+
| NULL |
+--------+
1 row in set (0.00 sec)mysql> SELECT NULL+NULL;
+-----------+
| NULL+NULL |
+-----------+
| NULL |
+-----------+
1 row in set (0.00 sec)比较运算符
（1）=, 比较字符串或数值是否相等，数值可直接和等值的字符串进行比较
mysql> SELECT 1=1;
+-----+
| 1=1 |
+-----+
| 1 |
+-----+
1 row in set (0.00 sec)mysql> SELECT 1=1,1='1';
+-----+-------+
| 1=1 | 1='1' |
+-----+-------+
| 1 | 1 |
+-----+-------+
1 row in set (0.00 sec)mysql> SELECT 1=1,1='1',1=2;
+-----+-------+-----+
| 1=1 | 1='1' | 1=2 |
+-----+-------+-----+
| 1 | 1 | 0 |
+-----+-------+-----+
1 row in set (0.00 sec)mysql> SELECT username,username='king' FROM student;
+----------+-----------------+
| username | username='king' |
+----------+-----------------+
| king | 1 |
| king1 | 0 |
| king2 | 0 |
| king3 | 0 |
| king4 | 0 |
| king5 | 0 |
| king6 | 0 |
| king7 | 0 |
| king8 | 0 |
+----------+-----------------+
9 rows in set (0.00 sec)mysql> SELECT username,username!='king' FROM student;
+----------+------------------+
| username | username!='king' |
+----------+------------------+
| king | 0 |
| king1 | 1 |
| king2 | 1 |
| king3 | 1 |
| king4 | 1 |
| king5 | 1 |
| king6 | 1 |
| king7 | 1 |
| king8 | 1 |
+----------+------------------+
9 rows in set (0.00 sec)（2）和NULL比较是否相等时要用<=>而不是=
mysql> SELECT id,username,age,sex,sex<=>NULL FROM cms_user;
+----+-----------+------+--------+------------+
| id | username | age | sex | sex<=>NULL |
+----+-----------+------+--------+------------+
| 1 | 张三 | 21 | 男 | 0 |
| 2 | 张三丰 | 31 | 女 | 0 |
| 3 | 章子怡 | 43 | 男 | 0 |
| 4 | long | 41 | 女 | 0 |
| 5 | ring | 9 | 男 | 0 |
| 6 | queen | 77 | 女 | 0 |
| 8 | blek | 85 | 女 | 0 |
| 9 | rose | 9 | 男 | 0 |
| 10 | lily | 39 | 女 | 0 |
| 11 | john | 72 | 保密 | 0 |
| 12 | test1 | NULL | 保密 | 0 |
| 13 | TEST2 | 18 | NULL | 1 |
| 14 | lll | 18 | NULL | 1 |
| 15 | ttt | 18 | NULL | 1 |
| 16 | ooo | 18 | NULL | 1 |
+----+-----------+------+--------+------------+
15 rows in set (0.00 sec)（3）>, <, >=, <=
mysql> SELECT id,username,score,score>=70 FROM student;
+----+----------+-------+-----------+
| id | username | score | score>=70 |
+----+----------+-------+-----------+
| 1 | king | 95 | 1 |
| 2 | king1 | 35 | 0 |
| 3 | king2 | 45 | 0 |
| 4 | king3 | 55 | 0 |
| 5 | king4 | 65 | 0 |
| 6 | king5 | 75 | 1 |
| 7 | king6 | 80 | 1 |
| 8 | king7 | 90 | 1 |
| 9 | king8 | 25 | 0 |
+----+----------+-------+-----------+
9 rows in set (0.00 sec)（4）IS NULL, IS NOT NULL
mysql> SELECT id,username,age,age IS NULL FROM cms_user;
+----+-----------+------+-------------+
| id | username | age | age IS NULL |
+----+-----------+------+-------------+
| 1 | 张三 | 21 | 0 |
| 2 | 张三丰 | 31 | 0 |
| 3 | 章子怡 | 43 | 0 |
| 4 | long | 41 | 0 |
| 5 | ring | 9 | 0 |
| 6 | queen | 77 | 0 |
| 8 | blek | 85 | 0 |
| 9 | rose | 9 | 0 |
| 10 | lily | 39 | 0 |
| 11 | john | 72 | 0 |
| 12 | test1 | NULL | 1 |
| 13 | TEST2 | 18 | 0 |
| 14 | lll | 18 | 0 |
| 15 | ttt | 18 | 0 |
| 16 | ooo | 18 | 0 |
+----+-----------+------+-------------+
15 rows in set (0.00 sec)mysql> SELECT id,username,age,age IS NOT NULL FROM cms_user;
+----+-----------+------+-----------------+
| id | username | age | age IS NOT NULL |
+----+-----------+------+-----------------+
| 1 | 张三 | 21 | 1 |
| 2 | 张三丰 | 31 | 1 |
| 3 | 章子怡 | 43 | 1 |
| 4 | long | 41 | 1 |
| 5 | ring | 9 | 1 |
| 6 | queen | 77 | 1 |
| 8 | blek | 85 | 1 |
| 9 | rose | 9 | 1 |
| 10 | lily | 39 | 1 |
| 11 | john | 72 | 1 |
| 12 | test1 | NULL | 0 |
| 13 | TEST2 | 18 | 1 |
| 14 | lll | 18 | 1 |
| 15 | ttt | 18 | 1 |
| 16 | ooo | 18 | 1 |
+----+-----------+------+-----------------+
15 rows in set (0.00 sec)（5）BETWEEN…AND…
mysql> SELECT id,username,age,age BETWEEN 10 AND 30 FROM cms_user;
+----+-----------+------+-----------------------+
| id | username | age | age BETWEEN 10 AND 30 |
+----+-----------+------+-----------------------+
| 1 | 张三 | 21 | 1 |
| 2 | 张三丰 | 31 | 0 |
| 3 | 章子怡 | 43 | 0 |
| 4 | long | 41 | 0 |
| 5 | ring | 9 | 0 |
| 6 | queen | 77 | 0 |
| 8 | blek | 85 | 0 |
| 9 | rose | 9 | 0 |
| 10 | lily | 39 | 0 |
| 11 | john | 72 | 0 |
| 12 | test1 | NULL | NULL |
| 13 | TEST2 | 18 | 1 |
| 14 | lll | 18 | 1 |
| 15 | ttt | 18 | 1 |
| 16 | ooo | 18 | 1 |
+----+-----------+------+-----------------------+
15 rows in set (0.02 sec)（6）IN
mysql> SELECT id,username,age,age IN(21,31,41,51) FROM cms_user;
+----+-----------+------+---------------------+
| id | username | age | age IN(21,31,41,51) |
+----+-----------+------+---------------------+
| 1 | 张三 | 21 | 1 |
| 2 | 张三丰 | 31 | 1 |
| 3 | 章子怡 | 43 | 0 |
| 4 | long | 41 | 1 |
| 5 | ring | 9 | 0 |
| 6 | queen | 77 | 0 |
| 8 | blek | 85 | 0 |
| 9 | rose | 9 | 0 |
| 10 | lily | 39 | 0 |
| 11 | john | 72 | 0 |
| 12 | test1 | NULL | NULL |
| 13 | TEST2 | 18 | 0 |
| 14 | lll | 18 | 0 |
| 15 | ttt | 18 | 0 |
| 16 | ooo | 18 | 0 |
+----+-----------+------+---------------------+
15 rows in set (0.00 sec)mysql> SELECT 1 IN (1,2,3);
+--------------+
| 1 IN (1,2,3) |
+--------------+
| 1 |
+--------------+
1 row in set (0.00 sec)mysql> SELECT 11 IN (1,2,3);
+---------------+
| 11 IN (1,2,3) |
+---------------+
| 0 |
+---------------+
1 row in set (0.00 sec)（7）LIKE
mysql> SELECT 's' LIKE '_';
+--------------+
| 's' LIKE '_' |
+--------------+
| 1 |
+--------------+
1 row in set (0.00 sec)mysql> SELECT 'sD' LIKE '_';
+---------------+
| 'sD' LIKE '_' |
+---------------+
| 0 |
+---------------+
1 row in set (0.00 sec)mysql> SELECT id,username,username LIKE '____' FROM cms_user;
+----+-----------+----------------------+
| id | username | username LIKE '____' |
+----+-----------+----------------------+
| 8 | blek | 1 |
| 11 | john | 1 |
| 10 | lily | 1 |
| 14 | lll | 0 |
| 4 | long | 1 |
| 16 | ooo | 0 |
| 6 | queen | 0 |
| 5 | ring | 1 |
| 9 | rose | 1 |
| 12 | test1 | 0 |
| 13 | TEST2 | 0 |
| 15 | ttt | 0 |
| 1 | 张三 | 0 |
| 2 | 张三丰 | 0 |
| 3 | 章子怡 | 0 |
+----+-----------+----------------------+
15 rows in set (0.00 sec)8）REGEXP
mysql> SELECT id,username,username REGEXP '^t' FROM cms_user;
+----+-----------+----------------------+
| id | username | username REGEXP '^t' |
+----+-----------+----------------------+
| 8 | blek | 0 |
| 11 | john | 0 |
| 10 | lily | 0 |
| 14 | lll | 0 |
| 4 | long | 0 |
| 16 | ooo | 0 |
| 6 | queen | 0 |
| 5 | ring | 0 |
| 9 | rose | 0 |
| 12 | test1 | 1 |
| 13 | TEST2 | 1 |
| 15 | ttt | 1 |
| 1 | 张三 | 0 |
| 2 | 张三丰 | 0 |
| 3 | 章子怡 | 0 |
+----+-----------+----------------------+
15 rows in set (0.00 sec)逻辑运算符
1）&&，AND，||，OR（和NULL运算时结果为NULL，但真值和NULL取或时结果为真）
mysql> SELECT 2&&2;
+------+
| 2&&2 |
+------+
| 1 |
+------+
1 row in set (0.00 sec)mysql> SELECT 2&&2,2&&0;
+------+------+
| 2&&2 | 2&&0 |
+------+------+
| 1 | 0 |
+------+------+
1 row in set (0.00 sec)mysql> SELECT 2&&2,2&&0,2&&NULL,1||1,1||0,1||NULL,0||NULL;
+------+------+---------+------+------+---------+---------+
| 2&&2 | 2&&0 | 2&&NULL | 1||1 | 1||0 | 1||NULL | 0||NULL |
+------+------+---------+------+------+---------+---------+
| 1 | 0 | NULL | 1 | 1 | 1 | NULL |
+------+------+---------+------+------+---------+---------+
1 row in set (0.00 sec)（2）！，NOT
mysql> SELECT NULL&&1;
+---------+
| NULL&&1 |
+---------+
| NULL |
+---------+
1 row in set (0.00 sec)mysql> SELECT !1,!0,!NULL;
+----+----+-------+
| !1 | !0 | !NULL |
+----+----+-------+
| 0 | 1 | NULL |
+----+----+-------+
1 row in set (0.00 sec)3）XOR
mysql> SELECT 1XOR0,0XOR1,1XOR1,0XOR0;
ERROR 1054 (42S22): Unknown column '1XOR0' in 'field list'
mysql> SELECT 1 XOR 0,0 XOR 1 ,1 XOR 1,0 XOR 0;
+---------+---------+---------+---------+
| 1 XOR 0 | 0 XOR 1 | 1 XOR 1 | 0 XOR 0 |
+---------+---------+---------+---------+
| 1 | 1 | 0 | 0 |
+---------+---------+---------+---------+
1 row in set (0.00 sec)MySQL运算符
数字函数
（1）CEIL()：进一取整
mysql> SELECT CEIL(1.2),CEILING(1.2);
+-----------+--------------+
| CEIL(1.2) | CEILING(1.2) |
+-----------+--------------+
| 2 | 2 |
+-----------+--------------+
1 row in set (0.00 sec)mysql> SELECT *FROM test4;
+------+------+------+
| num1 | num2 | num3 |
+------+------+------+
| 3.14 | 3.14 | 3.14 |
| 3.25 | 3.25 | 3.25 |
+------+------+------+
2 rows in set (0.07 sec)mysql> SELECT num1,CEIL(num2),CEILING(num3) FROM test4;
+------+------------+---------------+
| num1 | CEIL(num2) | CEILING(num3) |
+------+------------+---------------+
| 3.14 | 4 | 4 |
| 3.25 | 4 | 4 |
+------+------------+---------------+
2 rows in set (0.00 sec)（2）FLOOR()：舍一取整
mysql> SELECT FLOOR(3.14);
+-------------+
| FLOOR(3.14) |
+-------------+
| 3 |
+-------------+
1 row in set (0.00 sec)3）MOD：取余数（去模）
mysql> SELECT MOD(3,8);
+----------+
| MOD(3,8) |
+----------+
| 3 |
+----------+
1 row in set (0.00 sec)（4）POWER()：幂运算
mysql> SELECT POW(2,3),POWER(3,3);
+----------+------------+
| POW(2,3) | POWER(3,3) |
+----------+------------+
| 8 | 27 |
+----------+------------+
1 row in set (0.06 sec)5）ROUND()：四舍五入
mysql> SELECT ROUND(3.14567,2);
+------------------+
| ROUND(3.14567,2) |
+------------------+
| 3.15 |
+------------------+
1 row in set (0.02 sec)（6）TRUNCATE()：数字截取
mysql> SELECT TRUNCATE(3.14567,2);
+---------------------+
| TRUNCATE(3.14567,2) |
+---------------------+
| 3.14 |
+---------------------+
1 row in set (0.00 sec)（7）ABS()：取绝对值
mysql> SELECT ABS(-12);
+----------+
| ABS(-12) |
+----------+
| 12 |
+----------+
1 row in set (0.00 sec)（8）PI()：圆周率
mysql> SELECT PI();
+----------+
| PI() |
+----------+
| 3.141593 |
+----------+
1 row in set (0.01 sec)（9）RAND()和RAND(x)：返回0~1之间的随机数，RAND(x)x相同时返回的随机数相同
mysql> SELECT RAND();
+--------------------+
| RAND() |
+--------------------+
| 0.6808652986594153 |
+--------------------+
1 row in set (0.00 sec)mysql> SELECT RAND();
+--------------------+
| RAND() |
+--------------------+
| 0.7984468916416605 |
+--------------------+
1 row in set (0.00 sec)mysql> SELECT RAND(1);
+---------------------+
| RAND(1) |
+---------------------+
| 0.40540353712197724 |
+---------------------+
1 row in set (0.00 sec)mysql> SELECT RAND(1);
+---------------------+
| RAND(1) |
+---------------------+
| 0.40540353712197724 |
+---------------------+
1 row in set (0.00 sec)（10）SIGN(x)：返回x的符号，x为负数、0、正数分别返回-1、0、1
mysql> SELECT SIGN(12),SIGN(0),SIGN(-12);
+----------+---------+-----------+
| SIGN(12) | SIGN(0) | SIGN(-12) |
+----------+---------+-----------+
| 1 | 0 | -1 |
+----------+---------+-----------+
1 row in set (0.00 sec)（11）EXP(x)：计算e的几次方
mysql> SELECT EXP(3);
+--------------------+
| EXP(3) |
+--------------------+
| 20.085536923187668 |
+--------------------+
1 row in set (0.03 sec)字符串函数
（1）CHAR_LENGTH(S)：返回字符串的字符数；LENGTH：返回字符串长度
mysql> SELECT CHAR_LENGTH('maizi'),LENGTH('maizi');
+----------------------+-----------------+
| CHAR_LENGTH('maizi') | LENGTH('maizi') |
+----------------------+-----------------+
| 5 | 5 |
+----------------------+-----------------+
1 row in set (0.00 sec)mysql> SELECT CHAR_LENGTH('啊'),LENGTH('啊');
+--------------------+---------------+
| CHAR_LENGTH('啊') | LENGTH('啊') |
+--------------------+---------------+
| 1 | 3 |
+--------------------+---------------+
1 row in set (0.00 sec)2）CONTACT(S1, S2…)：将字符串合并为一个字符串，和NULL连接时结果为NULL
mysql> SELECT CONCAT('HELLO','WORLD');
+-------------------------+
| CONCAT('HELLO','WORLD') |
+-------------------------+
| HELLOWORLD |
+-------------------------+
1 row in set (0.02 sec)mysql> USE cms;
Database changed
mysql> SELECT * FROM student;
+----+----------+-------+
| id | username | score |
+----+----------+-------+
| 1 | king | 95 |
| 2 | king1 | 35 |
| 3 | king2 | 45 |
| 4 | king3 | 55 |
| 5 | king4 | 65 |
| 6 | king5 | 75 |
| 7 | king6 | 80 |
| 8 | king7 | 90 |
| 9 | king8 | 25 |
+----+----------+-------+
9 rows in set (0.00 sec)mysql> SELECT id,CONCAT(username,'_')FROM student;
+----+----------------------+
| id | CONCAT(username,'_') |
+----+----------------------+
| 1 | king_ |
| 2 | king1_ |
| 3 | king2_ |
| 4 | king3_ |
| 5 | king4_ |
| 6 | king5_ |
| 7 | king6_ |
| 8 | king7_ |
| 9 | king8_ |
+----+----------------------+
9 rows in set (0.00 sec)mysql> SELECT CONCAT('a','b',null);
+----------------------+
| CONCAT('a','b',null) |
+----------------------+
| NULL |
+----------------------+
1 row in set (0.00 sec)3）CONTACT_WS(X, S1, S2…)：将制定分隔符连接字符串，当X为NULL时，连接结果为NULL，当S1或S2…为NULL时当做空字符处理
mysql> SELECT CONCAT_WS('^_^','a','b','c');
+------------------------------+
| CONCAT_WS('^_^','a','b','c') |
+------------------------------+
| a^_^b^_^c |
+------------------------------+
1 row in set (0.00 sec)mysql> SELECT CONCAT_WS('','a','b','c');
+---------------------------+
| CONCAT_WS('','a','b','c') |
+---------------------------+
| abc |
+---------------------------+
1 row in set (0.00 sec)mysql> SELECT CONCAT_WS(NULL,'a','b','c');
+-----------------------------+
| CONCAT_WS(NULL,'a','b','c') |
+-----------------------------+
| NULL |
+-----------------------------+
1 row in set (0.00 sec)mysql> SELECT CONCAT_WS('^_^','a','b','c',NULL);
+-----------------------------------+
| CONCAT_WS('^_^','a','b','c',NULL) |
+-----------------------------------+
| a^_^b^_^c |
+-----------------------------------+
1 row in set (0.00 sec)4）UPPER(S)/UCASE(S)：将字符转换为大写
mysql> SELECT UPPER('this is a test'),UCASE('this is a test');
+-------------------------+-------------------------+
| UPPER('this is a test') | UCASE('this is a test') |
+-------------------------+-------------------------+
| THIS IS A TEST | THIS IS A TEST |
+-------------------------+-------------------------+
1 row in set (0.00 sec)
（5）LOWER(S)/LCASE(S)：将字符转换为小写
mysql> SELECT LOWER('HELLO WORLD'),LCASE('HELLO WORLD');
+----------------------+----------------------+
| LOWER('HELLO WORLD') | LCASE('HELLO WORLD') |
+----------------------+----------------------+
| hello world | hello world |
+----------------------+----------------------+
1 row in set (0.00 sec)
（6）LEFT(S, N)/RIGHT(S, N)：返回字符串的前/后n个字符
mysql> SELECT LEFT('ABCDEF',2),RIGHT('ABCDEF',2);
+------------------+-------------------+
| LEFT('ABCDEF',2) | RIGHT('ABCDEF',2) |
+------------------+-------------------+
| AB | EF |
+------------------+-------------------+
1 row in set (0.01 sec)
（7）LPAD(S1, LEN, S2)/ RPAD(S1, LEN, S2)：将字符串S1用S2填充到指定的LEN
mysql> SELECT LPAD('A',5,'?'),RPAD('A',5,'!');
+-----------------+-----------------+
| LPAD('A',5,'?') | RPAD('A',5,'!') |
+-----------------+-----------------+
| ????A | A!!!! |
+-----------------+-----------------+
1 row in set (0.04 sec)
（8）LTRIN(S)/ RTRIM(S)/ TRIM(S)：去掉字符串中的空格
mysql> SELECT CONCAT('_',TRIM(' ABC '),'_'),CONCAT('_',LTRIM(' ABC '),'_'),CONCAT('_',RTRIM(' ABC '),'_');
+-------------------------------+--------------------------------+--------------------------------+
| CONCAT('_',TRIM(' ABC '),'_') | CONCAT('_',LTRIM(' ABC '),'_') | CONCAT('_',RTRIM(' ABC '),'_') |
+-------------------------------+--------------------------------+--------------------------------+
| _ABC_ | _ABC _ | _ ABC_ |
+-------------------------------+--------------------------------+--------------------------------+
1 row in set (0.00 sec)
（9）TRIM(S1 FROM S)：去掉字符串s中开始处和结尾处的字符串s1
mysql> SELECT TRIM('A' FROM 'ABCBCA');
+-------------------------+
| TRIM('A' FROM 'ABCBCA') |
+-------------------------+
| BCBC |
+-------------------------+
1 row in set (0.00 sec)
（10）REPEAT(S,N)：重复字符串指定次数
mysql> SELECT REPEAT('H',5);
+---------------+
| REPEAT('H',5) |
+---------------+
| HHHHH |
+---------------+
1 row in set (0.00 sec)
（11）SPACE(N)：返回N个空格
mysql> SELECT CONCAT('_',SPACE(5),'_');
+--------------------------+
| CONCAT('_',SPACE(5),'_') |
+--------------------------+
| _ _ |
+--------------------------+
1 row in set (0.00 sec)
（12）REPLACE(S,S1,S2)：在字符串中搜索S1，替换成S2（区分大小写，若未搜索到则返回原字符串）
mysql> SELECT REPLACE('ABCBCA','A','_');
+---------------------------+
| REPLACE('ABCBCA','A','_') |
+---------------------------+
| _BCBC_ |
+---------------------------+
1 row in set (0.00 sec)mysql> SELECT REPLACE('ABCBCA','a','_');
+---------------------------+
| REPLACE('ABCBCA','a','_') |
+---------------------------+
| ABCBCA |
+---------------------------+
1 row in set (0.00 sec)
（13）STRCMP(S1, S2)：比较字符串，不区分大小写，>=<分别返回1，0，-1
mysql> SELECT STRCMP('A','A'),STRCMP('A','a'),STRCMP('B','A');
+-----------------+-----------------+-----------------+
| STRCMP('A','A') | STRCMP('A','a') | STRCMP('B','A') |
+-----------------+-----------------+-----------------+
| 0 | 0 | 1 |
+-----------------+-----------------+-----------------+
1 row in set (0.02 sec)mysql> SELECT STRCMP('A','A'),STRCMP('A','a'),STRCMP('A','B');
+-----------------+-----------------+-----------------+
| STRCMP('A','A') | STRCMP('A','a') | STRCMP('A','B') |
+-----------------+-----------------+-----------------+
| 0 | 0 | -1 |
+-----------------+-----------------+-----------------+
1 row in set (0.00 sec)
（14）SUBSTRING(S, N, LEN)：截取字符串
mysql> SELECT SUBSTRING('ABCDEF',2,2);
+-------------------------+
| SUBSTRING('ABCDEF',2,2) |
+-------------------------+
| BC |
+-------------------------+
1 row in set (0.00 sec)
（15）REVERSE(S)：反转字符串
mysql> SELECT REVERSE('ABC');
+----------------+
| REVERSE('ABC') |
+----------------+
| CBA |
+----------------+
1 row in set (0.00 sec)
（16）ELT(N, S1, S2)：返回指定位置的字符串
mysql> SELECT ELT(2,'A','B','C');
+--------------------+
| ELT(2,'A','B','C') |
+--------------------+
| B |
+--------------------+
1 row in set (0.00 sec)
日期时间函数
（1）CURDATE(), CURRENT_DATE()：返回当前日期
mysql> SELECT CURDATE(),CURRENT_DATE();
+------------+----------------+
| CURDATE() | CURRENT_DATE() |
+------------+----------------+
| 2020-03-27 | 2020-03-27 |
+------------+----------------+
1 row in set (0.04 sec)
（2）CURTIME(), CURRENT_TIME()：返回当前时间
mysql> SELECT CURTIME(),CURRENT_TIME();
+-----------+----------------+
| CURTIME() | CURRENT_TIME() |
+-----------+----------------+
| 15:59:32 | 15:59:32 |
+-----------+----------------+
1 row in set (0.00 sec)
（3）NOW()：返回当前日期和时间
mysql> SELECT NOW();
+---------------------+
| NOW() |
+---------------------+
| 2020-03-27 15:59:37 |
+---------------------+
1 row in set (0.00 sec)
（4）MONTH(D)：返回当前日期中月份的值
mysql> SELECT MONTH('2015-1-3');
+-------------------+
| MONTH('2015-3-27') |
+-------------------+
| 3 |
+-------------------+
1 row in set (0.00 sec)mysql> SELECT MONTH(NOW());
+--------------+
| MONTH(NOW()) |
+--------------+
| 3 |
+--------------+
1 row in set (0.00 sec)
（5）MONTHNAME(D)：返回日期中月份名称
mysql> SELECT MONTHNAME(NOW());
+------------------+
| MONTHNAME(NOW()) |
+------------------+
| March |
+------------------+
1 row in set (0.09 sec)
（6）DAYNAME(D)：返回日期是几
mysql> SELECT DAYNAME(NOW());
+----------------+
| DAYNAME(NOW()) |
+----------------+
| Friday |
+----------------+
1 row in set (0.02 sec)
（7）DAYOFWEEK(D)：返回一周内的第几天，1代表星期日
mysql> SELECT DAYOFWEEK(NOW());
+------------------+
| DAYOFWEEK(NOW()) |
+------------------+
| 6 |
+------------------+
1 row in set (0.00 sec)
（8）WEEKDAY(D)：返回日期是星期几，0代表星期一
mysql> SELECT WEEKDAY(NOW());
+----------------+
| WEEKDAY(NOW()) |
+----------------+
| 6 |
+----------------+
1 row in set (0.00 sec)
（9）WEEK(D)：一年中的第几个星期
mysql> SELECT WEEK(NOW());
+-------------+
| WEEK(NOW()) |
+-------------+
| 14 |
+-------------+
1 row in set (0.00 sec)
（10）YEAR(D)：返回年份值
mysql> SELECT YEAR(NOW());
+-------------+
| YEAR(NOW()) |
+-------------+
| 2020 |
+-------------+
1 row in set (0.00 sec)
（11）HOUR(T)：返回小时值
mysql> SELECT HOUR(NOW());
+-------------+
| HOUR(NOW()) |
+-------------+
| 16 |
+-------------+
1 row in set (0.00 sec)
（12）MINUTE(T)：返回分钟值
mysql> SELECT MINUTE(NOW());
+---------------+
| MINUTE(NOW()) |
+---------------+
| 1 |
+---------------+
1 row in set (0.00 sec)
（13）SECOND(T)：返回秒数
mysql> SELECT SECOND(NOW());
+---------------+
| SECOND(NOW()) |
+---------------+
| 49 |
+---------------+
1 row in set (0.00 sec)
（14）DATEDIFF(D1, D2)：计算量日期之间相隔的天数
mysql> SELECT DATEDIFF(CURRENT_DATE(),'1990-1-1');
+-------------------------------------+
| DATEDIFF(CURRENT_DATE(),'1990-1-1') |
+-------------------------------------+
| 9133 |
+-------------------------------------+
1 row in set (0.02 sec)
条件函数
（1）IF(EXPR, V1, V2)：如果表达式EXPR成立，则返回结果V1，否则返回V2
mysql> USE cms;
Database changed
mysql> SELECT * FROM student;
+----+----------+-------+
| id | username | score |
+----+----------+-------+
| 1 | king | 95 |
| 2 | king1 | 35 |
| 3 | king2 | 45 |
| 4 | king3 | 55 |
| 5 | king4 | 65 |
| 6 | king5 | 75 |
| 7 | king6 | 80 |
| 8 | king7 | 90 |
| 9 | king8 | 25 |
+----+----------+-------+
9 rows in set (0.00 sec)mysql> SELECT id,username,score,IF(score>=60,'及格','不及格')FROM student;
+----+----------+-------+------------------------------------+
| id | username | score | IF(score>=60,'及格','不及格') |
+----+----------+-------+------------------------------------+
| 1 | king | 95 | 及格 |
| 2 | king1 | 35 | 不及格 |
| 3 | king2 | 45 | 不及格 |
| 4 | king3 | 55 | 不及格 |
| 5 | king4 | 65 | 及格 |
| 6 | king5 | 75 | 及格 |
| 7 | king6 | 80 | 及格 |
| 8 | king7 | 90 | 及格 |
| 9 | king8 | 25 | 不及格 |
+----+----------+-------+------------------------------------+
9 rows in set (0.03 sec)（2）IFNULL(V1,V2)：如果V1不为空，就显示V1的值，否则显示V2的值
mysql> SELECT id,username,age,IFNULL(age,'100')FROM cms_user;
+----+-----------+------+-------------------+
| id | username | age | IFNULL(age,'100') |
+----+-----------+------+-------------------+
| 1 | 张三 | 21 | 21 |
| 2 | 张三丰 | 31 | 31 |
| 3 | 章子怡 | 43 | 43 |
| 4 | long | 41 | 41 |
| 5 | ring | 9 | 9 |
| 6 | queen | 77 | 77 |
| 8 | blek | 85 | 85 |
| 9 | rose | 9 | 9 |
| 10 | lily | 39 | 39 |
| 11 | john | 72 | 72 |
| 12 | test1 | NULL | 100 |
| 13 | TEST2 | 18 | 18 |
| 14 | lll | 18 | 18 |
| 15 | ttt | 18 | 18 |
| 16 | ooo | 18 | 18 |
+----+-----------+------+-------------------+
15 rows in set (0.00 sec)
（3）CASE WHEN exp1 THEN vi [WHEN exp2 THEN v2] [ELSE vn] END
mysql> SELECT id,username,score, CASE WHEN score>60 THEN '不错' WHEN score=60 THEN '刚及格' ELSE '没及格' END FROM student;
+----+----------+-------+--------------------------------------------------------------------------------------+
| id | username | score | CASE WHEN score>60 THEN '不错' WHEN score=60 THEN '刚及格' ELSE '没及格' END |
+----+----------+-------+--------------------------------------------------------------------------------------+
| 1 | king | 95 | 不错 |
| 2 | king1 | 35 | 没及格 |
| 3 | king2 | 45 | 没及格 |
| 4 | king3 | 55 | 没及格 |
| 5 | king4 | 65 | 不错 |
| 6 | king5 | 75 | 不错 |
| 7 | king6 | 80 | 不错 |
| 8 | king7 | 90 | 不错 |
| 9 | king8 | 25 | 没及格 |
+----+----------+-------+--------------------------------------------------------------------------------------+
9 rows in set (0.00 sec)
系统信息函数
加密函数
1）MD5(str)：信息摘要算法
mysql> SELECT MD5('ADMIN');
+----------------------------------+
| MD5('ADMIN') |
+----------------------------------+
| 73acd9a5972130b75066c82595a1fae3 |
+----------------------------------+
1 row in set (0.07 sec)
mysql> SELECT LENGTH(MD5('ADMIN'));
+----------------------+
| LENGTH(MD5('ADMIN')) |
+----------------------+
| 32 |
+----------------------+
1 row in set (0.00 sec
)
（2）PASSWORD(str)：密码算法（例如对用户设置密码）
mysql> SELECT PASSWORD('root'),PASSWORD('king');
+-------------------------------------------+-------------------------------------------+
| PASSWORD('root') | PASSWORD('king') |
+-------------------------------------------+-------------------------------------------+
| *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B | *0C6F8A2CE8ABFD18609CCE4CDFAB3C15DAD20718 |
+-------------------------------------------+-------------------------------------------+
1 row in set (0.02 sec)
（3）ENCODE(str, pwd_str)：加密结果是一二进制数，必须使用BLOB类型保存字段
（4）DECODE(crypt_str, pwd_str)：通过对ENCODE加密后的内容进行解密
其他常用函数
1）FORMAT(x, n)：将数字x进行格式化，并将x保留到小数点后n为
mysql> SELECT FORMAT(3.14567,2);
+-------------------+
| FORMAT(3.14567,2) |
+-------------------+
| 3.15 |
+-------------------+
1 row in set (0.00 sec)
（2）ASCII(s)：返回字符串的第一个字符的ASCII码
mysql> SELECT ASCII('abc');
+--------------+
| ASCII('abc') |
+--------------+
| 97 |
+--------------+
1 row in set (0.02 sec)
（3）BIN(x)：返回x的二进制编码，HEX(x)：返回x的十六进制编码，OCT(x)：返回x的八进制编码
mysql> SELECT BIN(5),HEX(5),OCT(5);
+--------+--------+--------+
| BIN(5) | HEX(5) | OCT(5) |
+--------+--------+--------+
| 101 | 5 | 5 |
+--------+--------+--------+
1 row in set (0.02 sec)
（4）CONV(x, f1, f2)：将x从f1进制数编程f2进制数
mysql> SELECT CONV(5,10,2);
+--------------+
| CONV(5,10,2) |
+--------------+
| 101 |
+--------------+
1 row in set (0.00 sec)mysql> SELECT CONV(35,10,2);
+---------------+
| CONV(35,10,2) |
+---------------+
| 100011 |
+---------------+
1 row in set (0.00 sec)mysql> SELECT CONV(35,10,8);
+---------------+
| CONV(35,10,8) |
+---------------+
| 43 |
+---------------+
1 row in set (0.00 sec)mysql> SELECT CONV(35,10,16);
+----------------+
| CONV(35,10,16) |
+----------------+
| 23 |
+----------------+
1 row in set (0.00 sec)
（5）INET_ATON(IP)：将IP地址转换为数字
mysql> SELECT INET_ATON('127.0.0.1');
+------------------------+
| INET_ATON('127.0.0.1') |
+------------------------+
| 2130706433 |
+------------------------+
1 row in set (0.06 sec)
（6）INET_NTOA(n)：将数字转换成IP地址
mysql> SELECT INET_NTOA(2130706433);
+-----------------------+
| INET_NTOA(2130706433) |
+-----------------------+
| 127.0.0.1 |
+-----------------------+
1 row in set (0.02 sec)
（7）get_LOCT(name, time)：定义锁
mysql> SELECT GET_LOCK('KING',10);
+---------------------+
| GET_LOCK('KING',10) |
+---------------------+
| 1 |
+---------------------+
1 row in set (0.05 sec)
（8）IS_FREE_LOCK(name)：判断锁是否正在使用，0表示正在使用，1表示未在使用，解锁或新建立锁都能使锁脱离被使用的状态
mysql> SELECT IS_FREE_LOCK('KING');
+----------------------+
| IS_FREE_LOCK('KING') |
+----------------------+
| 0 |
+----------------------+
1 row in set (0.02 sec)mysql> SELECT RELEASE_LOCK('KING');
+----------------------+
| RELEASE_LOCK('KING') |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)mysql> SELECT IS_FREE_LOCK('KING');
+----------------------+
| IS_FREE_LOCK('KING') |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)mysql> SELECT GET_LOCK('MAIZI',10);
+----------------------+
| GET_LOCK('MAIZI',10) |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)mysql> SELECT IS_FREE_LOCK('MAIZI');
+-----------------------+
| IS_FREE_LOCK('MAIZI') |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (0.00 sec)mysql> SELECT GET_LOCK('AB',5);
+------------------+
| GET_LOCK('AB',5) |
+------------------+
| 1 |
+------------------+
1 row in set (0.00 sec)mysql> SELECT IS_FREE_LOCK('MAIZI');
+-----------------------+
| IS_FREE_LOCK('MAIZI') |
+-----------------------+
| 1 |
+-----------------------+
1 row in set (0.00 sec)
（9）RELSASE_LOCK(name)：解锁
mysql> SELECT RELEASE_LOCK('KING');
+----------------------+
| RELEASE_LOCK('KING') |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)mysql> SELECT IS_FREE_LOCK('KING');
+----------------------+
| IS_FREE_LOCK('KING') |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)
MySQL索引
索引的概念
（1）索引由数据库中的一列或多列组合而成，其作用是提高对表中数据的查询速度
（2）索引的优点是可以提高检索数据的速度
（3）索引的缺点是创建和维护索引需要耗费时间
（4）索引可以提高查询速度，会减慢写入速度
索引的分类
（1）普通索引
（2）唯一索引
（3）全文索引
只有是字符类型且全是英文名时可使用
（4）单列索引
（5）多列索引
（6）空间索引
创建索引
创建表时创建索引
CREATE TABLE tbl_name(
字段名称 字段类型 [完整性约束条件], …, [UNIQUE | FULLTEXT | SPATIAL] INDEX | KEY [索引名称] (字段名称)
)
（1）创建普通索引
mysql> CREATE TABLE test4(-> id TINYINT UNSIGNED,-> username VARCHAR(20),-> INDEX in_id(id),-> KEY in_username(username)-> );
Query OK, 0 rows affected (0.42 sec)mysql> SHOW CREATE TABLE test4;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test4 | CREATE TABLE `test4` (`id` tinyint(3) unsigned DEFAULT NULL,`username` varchar(20) DEFAULT NULL,KEY `in_id` (`id`),KEY `in_username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.03 sec)
（2）创建唯一索引
mysql> CREATE TABLE test5(-> id TINYINT UNSIGNED AUTO_INCREMENT KEY,-> username VARCHAR(20) NOT NULL UNIQUE,-> card CHAR(18) NOT NULL,-> UNIQUE KEY uni_card(card)-> );
Query OK, 0 rows affected (0.47 sec)mysql> SHOW CREATE TABLE test5;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test5 | CREATE TABLE `test5` (`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,`username` varchar(20) NOT NULL,`card` char(18) NOT NULL,PRIMARY KEY (`id`),UNIQUE KEY `username` (`username`),UNIQUE KEY `uni_card` (`card`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
（3）创建全文索引
mysql> CREATE TABLE test6(-> id TINYINT UNSIGNED AUTO_INCREMENT KEY,-> username VARCHAR(20) NOT NULL UNIQUE,-> userDesc VARCHAR(20) NOT NULL,-> FULLTEXT INDEX full_userDesc(userDesc)-> );
Query OK, 0 rows affected (2.09 sec)mysql> SHOW CREATE TABLE test6;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test6 | CREATE TABLE `test6` (`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,`username` varchar(20) NOT NULL,`userDesc` varchar(20) NOT NULL,PRIMARY KEY (`id`),UNIQUE KEY `username` (`username`),FULLTEXT KEY `full_userDesc` (`userDesc`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
（4）创建单列索引
mysql> CREATE TABLE test7(-> id TINYINT UNSIGNED AUTO_INCREMENT KEY,-> test1 VARCHAR(20) NOT NULL,-> test2 VARCHAR(20) NOT NULL,-> test3 VARCHAR(20) NOT NULL,-> test4 VARCHAR(20) NOT NULL,-> INDEX in_test1(test1)-> );
Query OK, 0 rows affected (0.38 sec)mysql> SHOW CREATE TABLE test7;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test7 | CREATE TABLE `test7` (`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,`test1` varchar(20) NOT NULL,`test2` varchar(20) NOT NULL,`test3` varchar(20) NOT NULL,`test4` varchar(20) NOT NULL,PRIMARY KEY (`id`),KEY `in_test1` (`test1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)
（5）创建多列索引
mysql> CREATE TABLE test8(-> id TINYINT UNSIGNED AUTO_INCREMENT KEY,-> test1 VARCHAR(20) NOT NULL,-> test2 VARCHAR(20) NOT NULL,-> test3 VARCHAR(20) NOT NULL,-> test4 VARCHAR(20) NOT NULL,-> INDEX mul_t1_t2_t3(test1,test2,test3)-> );
Query OK, 0 rows affected (0.27 sec)mysql> SHOW CREATE TABLE test8;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test8 | CREATE TABLE `test8` (`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,`test1` varchar(20) NOT NULL,`test2` varchar(20) NOT NULL,`test3` varchar(20) NOT NULL,`test4` varchar(20) NOT NULL,PRIMARY KEY (`id`),KEY `mul_t1_t2_t3` (`test1`,`test2`,`test3`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql> DESC test8;
+-------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------------+------+-----+---------+----------------+
| id | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| test1 | varchar(20) | NO | MUL | NULL | |
| test2 | varchar(20) | NO | | NULL | |
| test3 | varchar(20) | NO | | NULL | |
| test4 | varchar(20) | NO | | NULL | |
+-------+---------------------+------+-----+---------+----------------+
5 rows in set (0.08 sec)
（6）创建空间索引（只能给空间变量创建空间索引）
mysql> CREATE TABLE test10(-> id TINYINT UNSIGNED AUTO_INCREMENT KEY,-> test GEOMETRY NOT NULL,-> SPATIAL INDEX spa_test(test)-> )ENGINE=MyISAM;
Query OK, 0 rows affected (0.06 sec)mysql> SHOW CREATE TABLE test10;
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test10 | CREATE TABLE `test10` (`id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,`test` geometry NOT NULL,PRIMARY KEY (`id`),SPATIAL KEY `spa_test` (`test`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.09 sec)
在已经存在的表上创建索引
【1】CREATE [UNIQUE | FULLTEXT | SPATIAL] INDEX 索引名称 ON 表名 {字段名称 [(长度)] [ASC|DESC]}
（1）普通索引
CREATE INDEX in_id ON test4(id)
（2）唯一索引
CREATE UNIQUE INDEX uni_username ON test5(username);
（3）全文索引
（4）单列索引
（5）多列索引
（6）空间索引
CREATE SPATIAL INDEX spa_test ON test10(test);
【2】ALTER TABLE tbl_name ADD [UNIQUE | FULLTEXT | SPATIAL] INDEX 索引名称(字段名称[(长度)] [ASC|DESC])
（1）普通索引
ALTER TABLE test4 ADD INDEX in_username(username)
（2）唯一索引
ALTER TABLE test5 ADD UNIQUE INDEX uni_card(card);
（3）全文索引
CREATE FULLTEXT INDEX full_userDesc ON test6(userDesc);
（4）单列索引
（5）多列索引
ALTER TABLE test8 ADD INDEX mul_ti_t2_t3(test1,test2,test3);
（6）空间索引
删除索引
【1】DROP INDEX 索引名称 ON tbl_name
DROP INDEX full_userDesc ON test6;
【2】ALTER tbl_name 表名 DROP INDEX 索引名称
ALTER TABLE test8 DROP INDEX mul_t1_t2_t3;
MySQL图形化管理工具
PHPMyAdmin
PHPMyAdmin是一个用PHP编写的软件工具，可以通过web方式控制和操作MySQL数据库
SQLyog
【1】是业界注明的Webyog公司出品的一款简介高效，功能强大的MySQL数据库管理工具
【2】特点：
（1）基于C++和MySQLQPI编程
（2）方便快捷的数据库同步与数据库结构同步工具
（3）易用的数据库，数据备份与还原功能（4）支持导入与导出XML、HTML、CSV等多种格式的数据
（5）直接运行批量SQL脚本文件，速度极快
（6）新版本更适合增加了强大的数据迁移
