Hive 简明教程

Hive - Alter Table

本章介绍如何修改表的属性，例如更改表名、更改列名、添加列以及删除或替换列。

This chapter explains how to alter the attributes of a table such as changing its table name, changing column names, adding columns, and deleting or replacing columns.

Alter Table Statement

用于在 Hive 中更改表格。

It is used to alter a table in Hive.

Syntax

该语句根据我们希望在表中修改哪些属性采用以下任一语法。

The statement takes any of the following syntaxes based on what attributes we wish to modify in a table.

ALTER TABLE name RENAME TO new_name
ALTER TABLE name ADD COLUMNS (col_spec[, col_spec ...])
ALTER TABLE name DROP [COLUMN] column_name
ALTER TABLE name CHANGE column_name new_name new_type
ALTER TABLE name REPLACE COLUMNS (col_spec[, col_spec ...])

Rename To… Statement

以下查询将表从 employee 重命名为 emp 。

The following query renames the table from employee to emp.

hive> ALTER TABLE employee RENAME TO emp;

JDBC Program

用于重命名表的 JDBC 程序如下。

The JDBC program to rename a table is as follows.

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

public class HiveAlterRenameTo {
   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("ALTER TABLE employee RENAME TO emp;");
      System.out.println("Table Renamed Successfully");
      con.close();
   }
}

将程序保存在名为 HiveAlterRenameTo.java 的文件中。使用以下命令来编译和执行此程序。

Save the program in a file named HiveAlterRenameTo.java. Use the following commands to compile and execute this program.

$ javac HiveAlterRenameTo.java
$ java HiveAlterRenameTo

Output:

Table renamed successfully.

Change Statement

下表包含 employee 表的字段，并显示要更改的字段（以粗体显示）。

The following table contains the fields of employee table and it shows the fields to be changed (in bold).

Field Name

Convert from Data Type

Change Field Name

Convert to Data Type

eid

int

eid

int

name

String

ename

String

salary

Float

salary

Double

designation

String

designation

String

以下查询使用上述数据重命名列名称和列数据类型：

The following queries rename the column name and column data type using the above data:

hive> ALTER TABLE employee CHANGE name ename String;
hive> ALTER TABLE employee CHANGE salary salary Double;

JDBC Program

以下是用于更改列的 JDBC 程序。

Given below is the JDBC program to change a column.

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

public class HiveAlterChangeColumn {
   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("ALTER TABLE employee CHANGE name ename String;");
      stmt.executeQuery("ALTER TABLE employee CHANGE salary salary Double;");

      System.out.println("Change column successful.");
      con.close();
   }
}

将程序保存在名为 HiveAlterChangeColumn.java 的文件中。使用以下命令来编译和执行此程序。

Save the program in a file named HiveAlterChangeColumn.java. Use the following commands to compile and execute this program.

$ javac HiveAlterChangeColumn.java
$ java HiveAlterChangeColumn

Output:

Change column successful.

Add Columns Statement

以下查询向 employee 表中添加一个名为 dept 的列。

The following query adds a column named dept to the employee table.

hive> ALTER TABLE employee ADD COLUMNS (
dept STRING COMMENT 'Department name');

JDBC Program

用于向表中添加列的 JDBC 程序如下。

The JDBC program to add a column to a table 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 HiveAlterAddColumn {
   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("ALTER TABLE employee ADD COLUMNS " + " (dept STRING COMMENT 'Department name');");
      System.out.prinln("Add column successful.");

      con.close();
   }
}

将程序保存在名为 HiveAlterAddColumn.java 的文件中。使用以下命令来编译和执行此程序。

Save the program in a file named HiveAlterAddColumn.java. Use the following commands to compile and execute this program.

$ javac HiveAlterAddColumn.java
$ java HiveAlterAddColumn

Output:

Add column successful.

Replace Statement

以下查询从 employee 表中删除所有列，并用 emp 和 name 列替换。

The following query deletes all the columns from the employee table and replaces it with emp and name columns:

hive> ALTER TABLE employee REPLACE COLUMNS (
eid INT empid Int,
ename STRING name String);

JDBC Program

以下是用于用 empid 和 ename *column with *name 替换 eid 列的 JDBC 程序。

Given below is the JDBC program to replace eid column with empid and ename *column with *name.

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

public class HiveAlterReplaceColumn {

   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("ALTER TABLE employee REPLACE COLUMNS "
         +" (eid INT empid Int,"
         +" ename STRING name String);");

      System.out.println(" Replace column successful");
      con.close();
   }
}

将程序保存在名为 HiveAlterReplaceColumn.java 的文件中。使用以下命令来编译和执行此程序。

Save the program in a file named HiveAlterReplaceColumn.java. Use the following commands to compile and execute this program.

$ javac HiveAlterReplaceColumn.java
$ java HiveAlterReplaceColumn

Output:

Replace column successful.