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标题: pig中各种sql语句的实现 [打印本页]

作者: 乔帮主 时间: 2014-10-17 20:34
标题: pig中各种sql语句的实现
本帖最后由乔帮主于 2014-10-17 20:35 编辑

Pig是一个基于Hadoop的大规模数据分析平台，它提供的SQL-LIKE语言叫Pig Latin，该语言的编译器会把类SQL的数据分析请求转换为一系列经过优化处理的MapReduce运算。使用pig可以在处理海量数据时达到事半功倍的效果，比使用Java，C++等语言编写大规模数据处理程序的难度要小N倍，实现同样的效果的代码量也小N倍。我们可以在不熟悉map/reduce的情况下使用类似与sql语句的pig latin语句来实现复杂的数据处理。
我这里以Mysql 5.1.x为例,Pig的版本是0.8
同时我将数据放在了两个文件,存放在/tmp/data_file_1和/tmp/data_file_2中.文件内容如下:
tmp_file_1:
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tmp_file_2:
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1.从文件导入数据
      1)Mysql (Mysql需要先创建表).
         CREATE TABLE TMP_TABLE(USER VARCHAR(32),AGE INT,IS_MALE BOOLEAN);
         CREATE TABLE TMP_TABLE_2(AGE INT,OPTIONS VARCHAR(50)); -- 用于Join
         LOAD DATA LOCAL INFILE '/tmp/data_file_1'  INTO TABLE TMP_TABLE ;
         LOAD DATA LOCAL INFILE '/tmp/data_file_2'  INTO TABLE TMP_TABLE_2;
      2)Pig
            tmp_table = LOAD '/tmp/data_file_1' USING PigStorage('\t') AS (user:chararray, age:int,is_male:int);
            tmp_table_2= LOAD '/tmp/data_file_2' USING PigStorage('\t') AS (age:int,options:chararray);

   2.查询整张表
      1)Mysql
         SELECT * FROM TMP_TABLE;
      2)Pig
         DUMP tmp_table;
   3. 查询前50行
      1)Mysql
         SELECT * FROM TMP_TABLE LIMIT 50;
      2)Pig
         tmp_table_limit = LIMIT tmp_table 50;
         DUMP tmp_table_limit;
   4.查询某些列
      1)Mysql
         SELECT USER FROM TMP_TABLE;
      2)Pig
         tmp_table_user = FOREACH tmp_table GENERATE user;
         DUMP tmp_table_user;

5. 给列取别名
      1)Mysql
         SELECT USER AS USER_NAME,AGE AS USER_AGE FROM TMP_TABLE;
      2)Pig
         tmp_table_column_alias = FOREACH tmp_table GENERATE user AS user_name,age AS user_age;
         DUMP tmp_table_column_alias;

   6.排序
      1)Mysql
         SELECT * FROM TMP_TABLE ORDER BY AGE;
      2)Pig
         tmp_table_order = ORDER tmp_table BY age ASC;
         DUMP tmp_table_order;

   7.条件查询
      1）Mysql
         SELECT * FROM TMP_TABLE WHERE AGE>20;
      2) Pig
         tmp_table_where = FILTER tmp_table by age > 20;
         DUMP tmp_table_where;

   8.内连接Inner Join
      1)Mysql
         SELECT * FROM TMP_TABLE A JOIN TMP_TABLE_2 B ON A.AGE=B.AGE;
      2)Pig
         tmp_table_inner_join = JOIN tmp_table BY age,tmp_table_2 BY age;
         DUMP tmp_table_inner_join;
9.左连接Left  Join
   1)Mysql
         SELECT * FROM TMP_TABLE A LEFT JOIN TMP_TABLE_2 B ON A.AGE=B.AGE;
   2)Pig
      tmp_table_left_join = JOIN tmp_table BY age LEFT OUTER,tmp_table_2 BY age;
      DUMP tmp_table_left_join;
10.右连接Right Join
      1)Mysql
         SELECT * FROM TMP_TABLE A RIGHT JOIN TMP_TABLE_2 B ON A.AGE=B.AGE;
      2)Pig
         tmp_table_right_join = JOIN tmp_table BY age RIGHT OUTER,tmp_table_2 BY age;
         DUMP tmp_table_right_join;
11.全连接Full Join
      1)Mysql
         SELECT * FROM TMP_TABLE A  JOIN TMP_TABLE_2 B ON A.AGE=B.AGE
            UNION SELECT * FROM TMP_TABLE A LEFT JOIN TMP_TABLE_2 B ON A.AGE=B.AGE
            UNION SELECT * FROM TMP_TABLE A RIGHT JOIN TMP_TABLE_2 B ON A.AGE=B.AGE;
      2)Pig
         tmp_table_full_join = JOIN tmp_table BY age FULL OUTER,tmp_table_2 BY age;
         DUMP tmp_table_full_join;

   12.同时对多张表交叉查询
      1)Mysql
         SELECT * FROM TMP_TABLE,TMP_TABLE_2;
      2)Pig
         tmp_table_cross = CROSS tmp_table,tmp_table_2;
         DUMP tmp_table_cross;

   13.分组GROUP BY
      1)Mysql
         SELECT * FROM TMP_TABLE GROUP BY IS_MALE;
      2)Pig
         tmp_table_group = GROUP tmp_table BY is_male;
         DUMP tmp_table_group;
    14.分组并统计
         1)Mysql
         SELECT IS_MALE,COUNT(*) FROM TMP_TABLE GROUP BY IS_MALE;
         2)Pig
            tmp_table_group_count = GROUP tmp_table BY is_male;
            tmp_table_group_count = FOREACH tmp_table_group_count GENERATE group,COUNT($1);
            DUMP tmp_table_group_count;

   15.查询去重DISTINCT
         1)MYSQL
            SELECT DISTINCT IS_MALE FROM TMP_TABLE;
         2)Pig
            tmp_table_distinct = FOREACH tmp_table GENERATE is_male;
            tmp_table_distinct = DISTINCT tmp_table_distinct;
            DUMP  tmp_table_distinct;

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