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知乎专栏

第 63 章 Functions and Operators

目录

63.1. COUNT
63.2. UUID()
63.3. 字符串
63.3.1. LEFT/RIGHT
63.3.2. RPAD/LPAD
63.3.3. CONCAT
63.3.4. CONCAT_WS
63.3.5. 链接所有字段
63.3.6. GROUP_CONCAT
63.3.7. replace 字符串替换
63.3.8. SUBSTRING
63.3.9. SUBSTRING_INDEX
63.3.10. AES_ENCRYPT / AES_DECRYPT
63.4. Date and Time
63.4.1. year/month/day hour:minite:second
63.4.2. Unix time
63.4.3. DATE_FORMAT
63.4.4. DATE_SUB/DATE_ADD
63.4.5. datediff / timediff
63.5. 数值函数
63.5.1. cast 类型转换
63.5.2. truncate 保留小数位数
63.5.3. MOD 求余
63.6. Control Flow Functions

63.1. COUNT

count()

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="group_concat">
		<title>group_concat() 列传行</title>
		<para></para>
		<screen><![CDATA[
SELECT tags FROM neo.article;

linux
redis
mysql
java
php
		

tags字段专为一行显示

SELECT group_concat(tags) FROM neo.article;		

linux,redis,mysql,java,php
		

distinct 去除重复数据

select group_concat(distinct author) from neo.article;		
		

以id分组,把name字段的值打印在一行,分号分隔

select id,group_concat(tags separator ';') from neo.article group by tags;		
		

排序结果

select group_concat(distinct author order by author desc) from neo.article;