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<?xml version="1.0" encoding="UTF-8"?>
<!-- $Id: chapter.sql.function.xml 555 2013-04-07 09:54:05Z netkiller $ -->
<chapter id="index"><?dbhtml dir="functions"?>
<title>Functions and Operators</title>
<section id="count">
<title>COUNT</title>
<para>count()</para>
<screen>
SELECT (SELECT count(1) FROM ecs_category) as 'Export category count',
(SELECT count(1) FROM ecs_goods) as 'Goods count',
(SELECT count(1) FROM ecs_goods_attr) as 'Attr count';
</screen>
</section>
<section id="uuid">
<title>UUID()</title>
<programlisting>
SELECT UUID(),LENGTH(UUID()),UUID_SHORT(), LENGTH(UUID_SHORT());
</programlisting>
</section>
<section id="string">
<title>String</title>
<section id="left">
<title>LEFT/RIGHT</title>
<para>LEFT(str,len)</para>
<screen>
mysql> select left(concat('1','0000000'),5) as number;
+--------+
| number |
+--------+
| 10000 |
+--------+
1 row in set (0.00 sec)
</screen>
<para>RIGHT(str,len)</para>
<screen>
mysql> select right(concat('0000000','1'),5) as number;
+--------+
| number |
+--------+
| 00001 |
+--------+
1 row in set (0.00 sec)
</screen>
</section>
<section id="rpad">
<title>RPAD/LPAD</title>
<para>补齐长度用'0'填充</para>
<command>RPAD(str,len,padstr)</command>
<screen>
mysql> select rpad('10',5,'0') as txt;
+-------+
| txt |
+-------+
| 10000 |
+-------+
1 row in set (0.01 sec)
</screen>
<command>LPAD(str,len,padstr)</command>
<screen>
mysql> select lpad('10',5,'0') as txt;
+-------+
| txt |
+-------+
| 00010 |
+-------+
1 row in set (0.00 sec)
</screen>
</section>
<section id="concat">
<title>CONCAT</title>
<para>CONCAT(str1,str2,...) </para>
<screen>
mysql> select concat('Neo',' ','Chen') as Name;
+----------+
| Name |
+----------+
| Neo Chen |
+----------+
1 row in set (0.00 sec)
</screen>
</section>
<section id="group_concat">
<title>GROUP_CONCAT</title>
<para></para>
<screen>
mysql> select GROUP_CONCAT(CONVERT( username , CHAR (16)) order by username desc) as username from test;
+-------------------------------------------+
| username |
+-------------------------------------------+
| jam,jam2,john,john2,john3,neo,neo1,neo2 |
+-------------------------------------------+
6 rows in set, 1 warning (0.01 sec)
</screen>
</section>
<section id="replace">
<title>replace</title>
<screen>
select replace(goods_desc,':8000','') from ecs_goods;
update ecs_goods set goods_desc=replace(goods_desc,':8000','');
</screen>
</section>
<section id="substring">
<title>SUBSTRING</title>
<screen>
<![CDATA[
mysql> SELECT SUBSTRING('netkiller',4,4);
+----------------------------+
| SUBSTRING('netkiller',4,4) |
+----------------------------+
| kill |
+----------------------------+
1 row in set (0.00 sec)
]]>
</screen>
<para>与left,right 相同的用法</para>
<screen>
select right('M2014030615410572307:DEPOSIT', 7);
SELECT SUBSTRING('M2014030615410572307:DEPOSIT', -7);
</screen>
</section>
<section>
<title>SUBSTRING_INDEX</title>
<screen>
SELECT SUBSTRING_INDEX('M2014030615410572307:DEPOSIT', ':', -1);
SELECT SUBSTRING_INDEX('M2014030615410572307:DEPOSIT', ':', 1);
</screen>
</section>
</section>
<section id="datetime">
<title>Date and Time</title>
<screen>
SELECT NOW(),CURRENT_TIMESTAMP(),SYSDATE();
</screen>
<section>
<title>year/month/day hour:minite:second</title>
<screen>
<![CDATA[
mysql> select year('2012-03-20');
+--------------------+
| year('2012-03-20') |
+--------------------+
| 2012 |
+--------------------+
1 row in set (0.00 sec)
mysql> select month('2012-03-20');
+---------------------+
| month('2012-03-20') |
+---------------------+
| 3 |
+---------------------+
1 row in set (0.00 sec)
mysql> select day('2012-03-20');
+-------------------+
| day('2012-03-20') |
+-------------------+
| 20 |
+-------------------+
1 row in set (0.00 sec)
mysql> select hour('12:30:55');
+------------------+
| hour('12:30:55') |
+------------------+
| 12 |
+------------------+
1 row in set (0.00 sec)
mysql> select minute('12:30:55');
+--------------------+
| minute('12:30:55') |
+--------------------+
| 30 |
+--------------------+
1 row in set (0.00 sec)
mysql> select second('12:30:55');
+--------------------+
| second('12:30:55') |
+--------------------+
| 55 |
+--------------------+
1 row in set (0.00 sec)
]]>
</screen>
</section>
<section>
<title>Unix time</title>
<screen>
<![CDATA[
mysql> SELECT UNIX_TIMESTAMP('2005-03-27 02:00:00');
+---------------------------------------+
| UNIX_TIMESTAMP('2005-03-27 02:00:00') |
+---------------------------------------+
| 1111885200 |
+---------------------------------------+
mysql> SELECT FROM_UNIXTIME(1111885200);
+---------------------------+
| FROM_UNIXTIME(1111885200) |
+---------------------------+
| 2005-03-27 03:00:00 |
+---------------------------+
]]>
</screen>
<programlisting>
<![CDATA[
SELECT UNIX_TIMESTAMP('2012-01-01 00:00:00');
SELECT UNIX_TIMESTAMP('2012-07-30 00:00:00');
SELECT UNIX_TIMESTAMP();
SELECT UNIX_TIMESTAMP('2009-08-06') ;
SELECT UNIX_TIMESTAMP( curdate( ) );
select FROM_UNIXTIME(UNIX_TIMESTAMP('2012-07-30 00:00:00'), '%Y-%m-%d');
SELECT FROM_UNIXTIME( 1249488000, '%Y年%m月%d日' );
select FROM_UNIXTIME(createtime, '%m') as month, count(1) as count from members where createtime BETWEEN UNIX_TIMESTAMP('2012-01-01 00:00:00') and UNIX_TIMESTAMP('2012-12-31 00:00:00') group by FROM_UNIXTIME(createtime, '%m');
select FROM_UNIXTIME(createtime, '%m') as month, count(1) as count from members where createtime BETWEEN UNIX_TIMESTAMP('2011-01-01 00:00:00') and UNIX_TIMESTAMP('2011-12-31 00:00:00') group by FROM_UNIXTIME(createtime, '%m');
select FROM_UNIXTIME(createtime, '%m-%d') as month, count(1) as count from members where createtime BETWEEN UNIX_TIMESTAMP('2011-01-01 00:00:00') and UNIX_TIMESTAMP('2011-12-31 00:00:00') group by FROM_UNIXTIME(createtime, '%m-%d');
select FROM_UNIXTIME(createtime, '%m-%d') as month, count(1) as count from members where createtime BETWEEN UNIX_TIMESTAMP('2012-01-01 00:00:00') and UNIX_TIMESTAMP('2012-12-31 00:00:00') group by FROM_UNIXTIME(createtime, '%m-%d');
]]>
</programlisting>
</section>
<section>
<title>DATE_FORMAT</title>
<para>DATE_FORMAT() 函数用于以不同的格式显示日期/时间数据。</para>
<screen>
语法
DATE_FORMAT(date,format)
date 参数是合法的日期。format 规定日期/时间的输出格式。
可以使用的格式有：
格式 描述
%a 缩写星期名
%b 缩写月名
%c 月，数值
%D 带有英文前缀的月中的天
%d 月的天，数值(00-31)
%e 月的天，数值(0-31)
%f 微秒
%H 小时 (00-23)
%h 小时 (01-12)
%I 小时 (01-12)
%i 分钟，数值(00-59)
%j 年的天 (001-366)
%k 小时 (0-23)
%l 小时 (1-12)
%M 月名
%m 月，数值(00-12)
%p AM 或 PM
%r 时间，12-小时（hh:mm:ss AM 或 PM）
%S 秒(00-59)
%s 秒(00-59)
%T 时间, 24-小时 (hh:mm:ss)
%U 周 (00-53) 星期日是一周的第一天
%u 周 (00-53) 星期一是一周的第一天
%V 周 (01-53) 星期日是一周的第一天，与 %X 使用
%v 周 (01-53) 星期一是一周的第一天，与 %x 使用
%W 星期名
%w 周的天 （0=星期日, 6=星期六）
%X 年，其中的星期日是周的第一天，4 位，与 %V 使用
%x 年，其中的星期一是周的第一天，4 位，与 %v 使用
%Y 年，4 位
%y 年，2 位
</screen>
<para>实例</para>
<screen>
下面的脚本使用 DATE_FORMAT() 函数来显示不同的格式。我们使用 NOW() 来获得当前的日期/时间：
DATE_FORMAT(NOW(),'%b %d %Y %h:%i %p')
DATE_FORMAT(NOW(),'%m-%d-%Y')
DATE_FORMAT(NOW(),'%d %b %y')
DATE_FORMAT(NOW(),'%d %b %Y %T:%f')
SELECT DATE_FORMAT(NOW(),'%Y-%m-%d');
select DATE_FORMAT(asctime,'%Y-%m-%d') as Date, count(1) as Count from logging where tag='www' and facility='login' group by DATE_FORMAT(asctime,'%Y-%m-%d') order by asctime desc;
</screen>
</section>
<section>
<title>DATE_SUB/DATE_ADD</title>
<para>当前时间向后推10天</para>
<programlisting>
<![CDATA[
mysql> select DATE_SUB(now(), INTERVAL 240 HOUR);
+------------------------------------+
| DATE_SUB(now(), INTERVAL 240 HOUR) |
+------------------------------------+
| 2012-03-09 10:26:03 |
+------------------------------------+
1 row in set (0.00 sec)
mysql> select DATE_SUB(now(), INTERVAL 24 HOUR);
+-----------------------------------+
| DATE_SUB(now(), INTERVAL 24 HOUR) |
+-----------------------------------+
| 2012-03-18 10:28:43 |
+-----------------------------------+
1 row in set (0.00 sec)
]]>
</programlisting>
<programlisting>
<![CDATA[
DELETE from Message where created < DATE_sub(now(), INTERVAL 240 HOUR);
select * from PRICES_HISTORY where DATE_FORMAT(TIME ,GET_FORMAT(DATE,'ISO')) = (
select if ( WEEKDAY(CURRENT_DATE())=6 , DATE_SUB(CURRENT_DATE(), INTERVAL 1 DAY) , CURRENT_DATE())
)
]]>
</programlisting>
<section>
<title>DATE_ADD</title>
<programlisting>
SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY);
</programlisting>
</section>
</section>
<section>
<title>datediff / timediff</title>
<para>计算时间差，两个时间相减结果</para>
<screen>
<![CDATA[
mysql> select timediff('22:20:00','17:30:00');
+---------------------------------+
| timediff('22:20:00','17:30:00') |
+---------------------------------+
| 04:50:00 |
+---------------------------------+
1 row in set (0.00 sec)
mysql> select datediff('2008-08-08 12:00:00', '2008-08-01 00:00:00');
+--------------------------------------------------------+
| datediff('2008-08-08 12:00:00', '2008-08-01 00:00:00') |
+--------------------------------------------------------+
| 7 |
+--------------------------------------------------------+
1 row in set (0.00 sec)
]]>
</screen>
</section>
</section>
<section id="numeric">
<title>数值函数</title>
<section>
<title>cast 类型转换</title>
<programlisting>
<![CDATA[
mysql> SELECT cast(SUBSTRING('123456789',1,4) as UNSIGNED) * 100;
+----------------------------------------------------+
| cast(SUBSTRING('123456789',1,4) as UNSIGNED) * 100 |
+----------------------------------------------------+
| 123400 |
+----------------------------------------------------+
1 row in set (0.00 sec)
]]>
</programlisting>
</section>
<section id="truncate">
<title>truncate 保留小数位数</title>
<programlisting>
<![CDATA[
select profit, deficit, concat(truncate((profit / deficit)*100,2),'%') as percentage from ((select count(*) as profit from angelfund where profit > 0) as profit, (select count(*) as deficit from angelfund where profit < 0) as deficit);
]]>
</programlisting>
</section>
<section>
<title>MOD 求余</title>
<screen>
<![CDATA[
mysql> select 9 mod 5;
+---------+
| 9 mod 5 |
+---------+
| 4 |
+---------+
1 row in set (0.00 sec)
mysql> select mod(5,2);
+----------+
| mod(5,2) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)
mysql> select mod(5,2);
]]>
</screen>
</section>
</section>
</chapter>