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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.
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