Hive SQL基础操作

创建表

hive

查看本地的文件
#Can execute local commands within CLI, place a command in between ! and ;
!cat data/text.txt;

文件的内容
user1,Funny Story,1343182026191
user2,Cool Deal,1343182133839
user4,Interesting Post,1343182154633
user5,Yet Another Blog,13431839394

建表
CREATE TABLE posts (user STRING, post STRING, time BIGINT)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ','
STORED AS TEXTFILE;

hive> show tables;
hive> describe posts;

加载数据

把文件加载到表中
LOAD DATA LOCAL INPATH 'text.txt'
OVERWRITE INTO TABLE posts;

– Load data from HDFS location
hive> LOAD DATA INPATH '/training/hive/user-posts.txt'
> OVERWRITE INTO TABLE posts;

– Load data from a local file system
hive> LOAD DATA LOCAL INPATH 'data/user-posts.txt'
> OVERWRITE INTO TABLE posts;

如果在hdfs里存在大量的同类型格式的文件，可以通过已有文件来建表

hive> CREATE EXTERNAL TABLE posts
> (user STRING, post STRING, time BIGINT)
> ROW FORMAT DELIMITED
> FIELDS TERMINATED BY ','
> STORED AS TEXTFILE
> LOCATION '/training/hive/';

测试一下是否在hdfs里
hdfs dfs -cat /user/hive/warehouse/posts/text.txt

查询数据

select count (1) from posts;
select * from posts where user="user2";
select * from posts where time<=1343182133839 limit 2;

DROP TABLE posts;
将会在hdfs系统里执行删除
hdfs dfs -ls /user/hive/warehouse/

带分区的表

为了提高性能，还可以使用分区，如果设置了分区，用户
在插入数据时必须指定一个分区

CREATE TABLE posts1 (user STRING, post STRING, time BIGINT)
PARTITIONED BY(country STRING)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ','
STORED AS TEXTFILE;

describe posts1;

用户在插入数据时必须指定一个分区
LOAD DATA LOCAL INPATH 'text.txt'
OVERWRITE INTO TABLE posts1 PARTITION(country='US');

LOAD DATA LOCAL INPATH 'text.txt'
OVERWRITE INTO TABLE posts1 PARTITION(country='AUSTRALIA');

显示已有的分区
show partitions posts;
hdfs dfs -ls -R /user/hive/warehouse/posts

查询
select * from posts where country='US' limit 10;

Join表

CREATE TABLE posts_likes (user STRING, post STRING, likes_count INT);
INSERT OVERWRITE TABLE posts_likes
> SELECT p.user, p.post, l.count
> FROM posts p JOIN likes l ON (p.user = l.user);

Outer Join表
SELECT p.*, l.*
FROM posts p LEFT OUTER JOIN likes l ON (p.user = l.user)
limit 10;
SELECT p.*, l.*
FROM posts p RIGHT OUTER JOIN likes l ON (p.user = l.user)
limit 10;
SELECT p.*, l.*
FROM posts p FULL OUTER JOIN likes l ON (p.user = l.user)
limit 10;
Resources

JDBC Program

import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;

public class HiveCreateTable {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";

public static void main(String[] args) throws SQLException {

// Register driver and create driver instance
Class.forName(driverName);

// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");

// create statement
Statement stmt = con.createStatement();

// execute statement
stmt.executeQuery("CREATE TABLE IF NOT EXISTS "
+" employee ( eid int, name String, "
+" salary String, destignation String)"
+" COMMENT ‘Employee details’"
+" ROW FORMAT DELIMITED"
+" FIELDS TERMINATED BY ‘\t’"
+" LINES TERMINATED BY ‘\n’"
+" STORED AS TEXTFILE;");

System.out.println(“ Table employee created.”);
con.close();
}
}

$ javac HiveCreateDb.java
$ java HiveCreateDb

import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager;

public class HiveQLWhere {
private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";

public static void main(String[] args) throws SQLException {

// Register driver and create driver instance
Class.forName(driverName);

// get connection
Connection con = DriverManager.getConnection("jdbc:hive://localhost:10000/userdb", "", "");

// create statement
Statement stmt = con.createStatement();

// execute statement
Resultset res = stmt.executeQuery("SELECT * FROM employee WHERE salary>30000;");

System.out.println("Result:");
System.out.println(" ID \t Name \t Salary \t Designation \t Dept ");

while (res.next()) {
System.out.println(res.getInt(1) + " " + res.getString(2) + " " + res.getDouble(3) + " " + res.getString(4) + " " + res.getString(5));
}
con.close();
}
}

$ javac HiveQLWhere.java
$ java HiveQLWhere