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知乎专栏

第 25 章 Functions and Operators

目录

25.1. COUNT
25.2. UUID()
25.3. 字符串
25.3.1. LEFT/RIGHT
25.3.2. RPAD/LPAD
25.3.3. CONCAT
25.3.4. CONCAT_WS
25.3.5. 链接所有字段
25.3.6. GROUP_CONCAT
25.3.7. replace 字符串替换
25.3.8. SUBSTRING
25.3.9. SUBSTRING_INDEX
25.3.10. AES_ENCRYPT / AES_DECRYPT
25.4. Date and Time
25.4.1. year/month/day hour:minite:second
25.4.2. Unix time
25.4.3. DATE_FORMAT
25.4.4. DATE_SUB/DATE_ADD
25.4.5. datediff / timediff
25.5. 数值函数
25.5.1. cast 类型转换
25.5.2. truncate 保留小数位数
25.5.3. MOD 求余
25.6. Control Flow Functions

25.1. 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;