【转】pig中各种sql语句的实现

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:
Txt代码  
zhangsan    23  1  
lisi    24  1  
wangmazi    30  1  
meinv   18  0  
dama    55  0  
   tmp_file_2:
Txt代码  
1   a  
23  bb  
50  ccc  
30  dddd  
66  eeeee  
 
       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;

 

 

【转自】http://www.open-open.com/lib/view/open1385173281604.html