常用统计分析 SQL 在 AWK 中的实现

本文主要讲述如何在 awk 中实现 SQL 的常用操作，当做个简单的 awk 入门分享。
虽然文中部分 awk 会有其它更简洁高效的 shell 命令去完成，亦或是其它语言去完成，
但这都不在本文的讨论范畴。

注：本文所用到的两个测试文件 user、consumer，分别模拟两张 SQL 表：

user 表，字段： 
id name  addr 

1 zhangsan hubei 
3 lisi tianjin 
4 wangmazi guangzhou 
2 wangwu beijing 

consumer 表，字段： 
id cost date 

1 15 20121213 
2 20 20121213 
3 100 20121213 
4 99 20121213 
1 25 20121114 
2 108 20121114 
3 100 20121114 
4 66 20121114 
1 15 20121213 
1 115 20121114 

测试环境： 
OS 版本： 
uname -a 
CYGWIN_NT-6.1 june-PC 1.7.9(0.237/5/3) 2011-03-29 10:10 i686 Cygwin 
awk 版本： 
awk --version 
GNU Awk 3.1.8 

1、查询整张表记录，where 条件过滤，关键词：where
select * from user; awk 1 user;
select * from consumer where cost > 100;
awk '$2>100' consumer


2、对某个字段去重，或者按记录去重，关键词：distinct
select distinct(date) from consumer;
awk '!a[$3]++{print $3}' consumer
select distinct(*) from consumer;
awk '!a[$0]++' consumer


3、记录按序输出，关键词：order by
select id from user order by id;
awk '{a[$1]}END{asorti(a);for(i=1;i<=length(a);i++){print a[i]}}' user


4、取前多少条记录，关键词：limit
select * from consumer limit 2;
awk 'NR<=2' consumer
awk 'NR>2{exit}1' consumer # performance is better


5、分组求和统计，关键词：group by、having、sum、count
select id, count(1), sum(cost) from consumer group by id having count(1) > 2;
awk '{a[$1]=a[$1]==""?$2:a[$1]","$2}END{for(i in a){c=split(a[i],b,",");if(c>2){sum=0;for(j in b){sum+=b[j]};print i"\t"c"\t"sum}}}' consumer


6、模糊查询，关键词：like（like属于通配，也可正则 REGEXP）
select name from user where name like 'wang%';
awk '$2 ~/^wang/{print $2}' user
select addr from user where addr like '%bei';
awk '/.*bei$/{print $3}' user
select addr from user where addr like '%bei%';
awk '$3 ~/bei/{print $3}' user


7、多表 join 关联查询，关键词：join
select a.* , b.* from user a inner join consumer b  on a.id = b.id and b.id = 2;
awk 'ARGIND==1{a[$1]=$0;next}{if(($1 in a)&&$1==2){print a[$1]"\t"$2"\t"$3}}' user consumer


8、多表水平联接，关键词：union all
select a.* from user a union all select b.* from user b;
awk 1 user user
select a.* from user a union select b.* from user b;
awk '!a[$0]++' user user


9、随机抽样统计，关键词：order by rand()
SELECT * FROM consumer ORDER BY RAND() LIMIT 2;
awk 'BEGIN{srand();while(i<2){k=int(rand()*10)+1;if(!(k in a)){a[k];i++}}}(NR in a)' consumer

 

转载地址：http://religiose.iteye.com/blog/1827495