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是一种数据库技术，可以定义数据库和表来分析结构化数据。 结构化数据分析的主题是以表格方式存储数据，并传递查询以对其进行分析。 本章介绍如何创建Hive数据库。 Hive包含一个名为default的默认数据库。

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.

下面以级联的形式删除数据库，这意味着在删除数据库之前删除相应的表。

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.

相对比较简单，主要是熟悉两个脚本的写法就够日常开发使用了,如果有SQL基础（不管是mssql，还是MySQL）这些一看就懂了。

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