Hive - Create Database & Drop Database

Hive is a database technology that can define databases and tables to analyze structured data. The theme for structured data analysis is to store the data in a tabular manner, and pass queries to analyze it. This chapter explains how to create Hive database. Hive contains a default database named default.

Hive是一種數據庫技術，可以定義數據庫和表來分析結構化數據。 結構化數據分析的主題是以表格方式存儲數據，並傳遞查詢以對其進行分析。 本章介紹如何創建Hive數據庫。 Hive包含一個名為default的默認數據庫。

Create Database Statement

Create Database is a statement used to create a database in Hive. A database in Hive is a namespace or a collection of tables. The syntax for this statement is as follows:

CREATE DATABASE|SCHEMA [IF NOT EXISTS] <database name>

 

Here, IF NOT EXISTS is an optional clause, which notifies the user that a database with the same name already exists. We can use SCHEMA in place of DATABASE in this command. The following query is executed to create a database named userdb:

hive> CREATE DATABASE [IF NOT EXISTS] userdb;

 

or

hive> CREATE SCHEMA userdb;

 

The following query is used to verify a databases list:

hive> SHOW DATABASES;
default
userdb

 

JDBC Program

The JDBC program to create a database is given below.

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

public class HiveCreateDb {
   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/default", "", "");
      Statement stmt = con.createStatement();
      
      stmt.executeQuery("CREATE DATABASE userdb");
      System.out.println(“Database userdb created successfully.”);
      
      con.close();
   }
}

 

Save the program in a file named HiveCreateDb.java. The following commands are used to compile and execute this program.

$ javac HiveCreateDb.java
$ java HiveCreateDb

 

Output:

Database userdb created successfully.

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Drop Database Statement

Drop Database is a statement that drops all the tables and deletes the database. Its syntax is as follows:

DROP DATABASE StatementDROP (DATABASE|SCHEMA) [IF EXISTS] database_name 
[RESTRICT|CASCADE];

 

The following queries are used to drop a database. Let us assume that the database name is userdb.

hive> DROP DATABASE IF EXISTS userdb;

 

The following query drops the database using CASCADE. It means dropping respective tables before dropping the database.

下面以級聯的形式刪除數據庫，這意味着在刪除數據庫之前刪除相應的表。

hive> DROP DATABASE IF EXISTS userdb CASCADE;

 

The following query drops the database using SCHEMA.

hive> DROP SCHEMA userdb;

 

This clause was added in Hive 0.6.

JDBC Program

The JDBC program to drop a database is given below.

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

public class HiveDropDb {
   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/default", "", "");
      Statement stmt = con.createStatement();
      stmt.executeQuery("DROP DATABASE userdb");
      
      System.out.println(“Drop userdb database successful.”);
      
      con.close();
   }
}

 

Save the program in a file named HiveDropDb.java. Given below are the commands to compile and execute this program.

$ javac HiveDropDb.java
$ java HiveDropDb

 

Output:

Drop userdb database successful.

相對比較簡單，主要是熟悉兩個腳本的寫法就夠日常開發使用了,如果有SQL基礎（不管是mssql，還是MySQL）這些一看就懂了。

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