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: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
10、行列转换,关键词:SUM(IF())、WITH ROLLUP
mysql 写法:http://my.oschina.net/leejun2005/blog/77796
awk 写法:http://hi.baidu.com/leejun_2005/item/2bac30c2b97e5e56ad00ef86
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