Hive - Alter Table

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.
It is used to alter a table in Hive.
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 ...])

The following query renames the table from employee to emp.
hive> ALTER TABLE employee RENAME TO emp;

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();
   }
}
Save the program in a file named HiveAlterRenameTo.java. Use the following commands to compile and execute this program.
$ javac HiveAlterRenameTo.java
$ java HiveAlterRenameTo

Table renamed successfully.

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

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();
   }
}
Save the program in a file named HiveAlterChangeColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterChangeColumn.java
$ java HiveAlterChangeColumn

Change column successful.

The following query adds a column named dept to the employee table.
hive> ALTER TABLE employee ADD COLUMNS ( 
dept STRING COMMENT 'Department name');

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();
   }
}
Save the program in a file named HiveAlterAddColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterAddColumn.java
$ java HiveAlterAddColumn

Add column successful.

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);

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();
   }
}
Save the program in a file named HiveAlterReplaceColumn.java. Use the following commands to compile and execute this program.
$ javac HiveAlterReplaceColumn.java
$ java HiveAlterReplaceColumn
Replace column successful.


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