MySQL管理与优化(4)_MySQL

来源：动视网责编：小采时间：2020-11-09 19:27:17

MySQL管理与优化(4)_MySQL

MySQL管理与优化(4)_MySQL: 常用函数字符串函数：常用的字符串函数 CONCAT(s1, s2, ...):依次连接字符串。 mysql> SELECT CONCAT('aa', 'bb'), CONCAT('abc', 'de', 'fgh');+--------------------+-------------------

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导读MySQL管理与优化(4)_MySQL: 常用函数字符串函数：常用的字符串函数 CONCAT(s1, s2, ...):依次连接字符串。 mysql> SELECT CONCAT('aa', 'bb'), CONCAT('abc', 'de', 'fgh');+--------------------+-------------------

常用函数

字符串函数：

常用的字符串函数

CONCAT(s1, s2, ...):依次连接字符串。

mysql> SELECT CONCAT('aa', 'bb'), CONCAT('abc', 'de', 'fgh');+--------------------+----------------------------+| CONCAT('aa', 'bb') | CONCAT('abc', 'de', 'fgh') |+--------------------+----------------------------+| aabb | abcdefgh |+--------------------+----------------------------+

INSERT(str, x, y, instr):将str从x位置开始的y个字符串替换为instr，索引从1开始。

mysql> SELECT INSERT('ilike2014', 2, 4, 'enjoy');+------------------------------------+| INSERT('ilike2014', 2, 4, 'enjoy') |+------------------------------------+| ienjoy2014 |+------------------------------------+

LPAD(str, n, pad):str长度不足n，则左填充pad。

mysql> SELECT LPAD('XXX', 12, '01');+-----------------------+| LPAD('XXX', 12, '01') |+-----------------------+| 010101010XXX |+-----------------------+

SUBSTRING(str, x, y): 求子串str[x..y]，索引从1开始。

mysql> SELECT SUBSTRING('abcdefg', 1, 3);+----------------------------+| SUBSTRING('abcdefg', 1, 3) |+----------------------------+| abc |+----------------------------+

数值函数：

MySQL常用的数值函数：

范例：

mysql> SELECT ABS(0.8), ABS(-0.8), CEIL(-0.8), CEIL(0.8), FLOOR(-0.8), FLOOR(0.8), MOD(15,10), MOD(1,11), MOD(NULL,10);+----------+-----------+------------+-----------+-------------+------------+------------+-----------+--------------+| ABS(0.8) | ABS(-0.8) | CEIL(-0.8) | CEIL(0.8) | FLOOR(-0.8) | FLOOR(0.8) | MOD(15,10) | MOD(1,11) | MOD(NULL,10) |+----------+-----------+------------+-----------+-------------+------------+------------+-----------+--------------+| 0.8 | 0.8 | 0 | 1 | -1 | 0 | 5 | 1 | NULL |+----------+-----------+------------+-----------+-------------+------------+------------+-----------+--------------+mysql> SELECT ROUND(1.235, 2), TRUNCATE(1.235, 2);+-----------------+--------------------+| ROUND(1.235, 2) | TRUNCATE(1.235, 2) |+-----------------+--------------------+| 1.24 | 1.23 |+-----------------+--------------------+

日期和时间函数：

常用的日期时间函数：

范例：

-- 列举当前时间mysql> SELECT CURDATE(), CURTIME(), NOW();+------------+-----------+---------------------+| CURDATE() | CURTIME() | NOW() |+------------+-----------+---------------------+| 2014-06-12 | 11:54:22 | 2014-06-12 11:54:22 |+------------+-----------+---------------------+-- 返回Unix时间戳mysql> SELECT UNIX_TIMESTAMP(now());+-----------------------+| UNIX_TIMESTAMP(now()) |+-----------------------+| 1402545326 |+-----------------------+-- 返回Unix时间戳对应的日期mysql> SELECT UNIX_TIMESTAMP(now());+-----------------------+| UNIX_TIMESTAMP(now()) |+-----------------------+| 1402545326 |+-----------------------+-- 现在是哪周，哪年mysql> SELECT WEEK(now()), YEAR(now());+-------------+-------------+| WEEK(now()) | YEAR(now()) |+-------------+-------------+| 23 | 2014 |+-------------+-------------+

MySQL中的日期时间格式化：

如：

mysql> SELECT DATE_FORMAT(now(), '%Y-%m-%d %H:%m:%s');+-----------------------------------------+| DATE_FORMAT(now(), '%Y-%m-%d %H:%m:%s') |+-----------------------------------------+| 2014-06-12 12:06:13 |+-----------------------------------------+

有关时间计算

MySQL中的日期时间间隔类型有：

范例：

mysql> SELECT now() current, DATE_ADD(now(), INTERVAL 31 DAY) after31days, DATE_ADD(now(), INTERVAL -7 DAY) before7days, DATE_ADD(now(), INTERVAL '1_2' YEAR_MONTH) after_1year_2month;+---------------------+---------------------+---------------------+---------------------+| current | after31days | before7days | after_1year_2month |+---------------------+---------------------+---------------------+---------------------+| 2014-06-12 22:48:49 | 2014-07-13 22:48:49 | 2014-06-05 22:48:49 | 2015-08-12 22:48:49 |+---------------------+---------------------+---------------------+---------------------+

流程函数：

MySQL中的流程函数：

范例：

-- 初始化数据mysql> CREATE TABLE salary (userid int, salary decimal(9, 2));Query OK, 0 rows affected (0.06 sec)mysql> INSERT INTO salary VALUES(1, 1000), (2, 2000), (3, 3000), (4, 4000), (5, 5000), (1, NULL);Query OK, 6 rows affected (0.02 sec)Records: 6 Duplicates: 0 Warnings: 0mysql> SELECT * FROM salary;+--------+---------+| userid | salary |+--------+---------+| 1 | 1000.00 || 2 | 2000.00 || 3 | 3000.00 || 4 | 4000.00 || 5 | 5000.00 || 1 | NULL |+--------+---------+-- 根据薪水高低判断薪水mysql> SELECT IF(salary>2000, 'high', 'low') FROM salary;+--------------------------------+| IF(salary>2000, 'high', 'low') |+--------------------------------+| low || low || high || high || high || low |+--------------------------------+-- IFNULL使用mysql> SELECT IFNULL(salary, 0) FROM salary;+-------------------+| IFNULL(salary, 0) |+-------------------+| 1000.00 || 2000.00 || 3000.00 || 4000.00 || 5000.00 || 0.00 |+-------------------+-- CASE WHEN使用mysql> SELECT CASE salary WHEN 1000 THEN 'low' WHEN 2000 THEN 'mid' ELSE 'high' end FROM salary;+-----------------------------------------------------------------------+| CASE salary WHEN 1000 THEN 'low' WHEN 2000 THEN 'mid' ELSE 'high' end |+-----------------------------------------------------------------------+| low || mid || high || high || high || high |+-----------------------------------------------------------------------+

其他常用函数：

MySQL中其他常用函数：

范例：

mysql> SELECT DATABASE(), VERSION(), USER();+------------+-----------+----------------+| DATABASE() | VERSION() | USER() |+------------+-----------+----------------+| test | 5.6.14 | root@localhost |+------------+-----------+----------------+mysql> SELECT DATABASE(), VERSION(), USER();+------------+-----------+----------------+| DATABASE() | VERSION() | USER() |+------------+-----------+----------------+| test | 5.6.14 | root@localhost |+------------+-----------+----------------+mysql> SELECT INET_ATON('192.168.141.129');+------------------------------+| INET_ATON('192.168.141.129') |+------------------------------+| 3232271745 |+------------------------------+-- 41位加密密码mysql> SELECT PASSWORD('111111');+-------------------------------------------+| PASSWORD('111111') |+-------------------------------------------+| *FD571203974BA9AFE270FE62151AE967ECA5E0AA |+-------------------------------------------+-- MD5值计算mysql> SELECT MD5('111111');+----------------------------------+| MD5('111111') |+----------------------------------+| 96e79218965eb72c92a549dd5a330112 |+----------------------------------+

MySQL更多函数可参考：

http://dev.mysql.com/doc/refman/5.7/en/functions.html

不吝指正。