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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

It is used to alter a table in Hive.

Syntax

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

The following query renames the table from employee to emp.

hive> ALTER TABLE employee RENAME TO emp;

JDBC Program

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

Output:

Table renamed successfully.

Change Statement

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

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

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

Output:

Change column successful.

Add Columns Statement

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

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

Output:

Add column successful.

Replace Statement

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

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

Output:

Replace column successful. Print Page Previous Next Advertisements