Deleting a Specific Cell in a Table

Using the delete command, you can delete a specific cell in a table. The syntax of delete command is as follows:

delete ‘<table name>’, ‘<row>’, ‘<column name >’, ‘<time stamp>’

Example

Here is an example to delete a specific cell. Here we are deleting the salary.

hbase(main):006:0> delete ''emp'', ''1'', ''personal data:city'',
1417521848375
0 row(s) in 0.0060 seconds

Deleting All Cells in a Table

Using the “deleteall” command, you can delete all the cells in a row. Given below is the syntax of deleteall command.

deleteall ‘<table name>’, ‘<row>’,

Example

Here is an example of “deleteall” command, where we are deleting all the cells of row1 of emp table.

hbase(main):007:0> deleteall ''emp'',''1''
0 row(s) in 0.0240 seconds

Verify the table using the scan command. A snapshot of the table after deleting the table is given below.

hbase(main):022:0> scan ''emp''

ROW                  COLUMN + CELL

2 column = personal data:city, timestamp = 1417524574905, value = chennai 

2 column = personal data:name, timestamp = 1417524556125, value = ravi

2 column = professional data:designation, timestamp = 1417524204, value = sr:engg

2 column = professional data:salary, timestamp = 1417524604221, value = 30000

3 column = personal data:city, timestamp = 1417524681780, value = delhi

3 column = personal data:name, timestamp = 1417524672067, value = rajesh
 
3 column = professional data:designation, timestamp = 1417523187, value = jr:engg

3 column = professional data:salary, timestamp = 1417524702514, value = 25000

Deleting Data Using Java API

You can delete data from an HBase table using the delete() method of the HTable class. Follow the steps given below to delete data from a table.

Step 1: Instantiate the Configuration Class

Configuration class adds HBase configuration files to its object. You can create a configuration object using the create() method of the the HbaseConfiguration class as shown below.

Configuration conf = HbaseConfiguration.create();

Step 2: Instantiate the HTable Class

You have a class called HTable, an implementation of Table in HBase. This class is used to communicate with a single HBase table. While instantiating this class, it accepts the configuration object and the table name as parameters. You can instantiate the HTable class as shown below.

HTable hTable = new HTable(conf, tableName); 

Step 3: Instantiate the Delete Class

Instantiate the Delete class by passing the rowid of the row that is to be deleted, in byte array format. You can also pass timestamp and Rowlock to this constructor.

Delete delete = new Delete(toBytes("row1"));

Step 4: Select the Data to be Deleted

You can delete the data using the delete methods of the Delete class. This class has various delete methods. Choose the columns or column families to be deleted using those methods. Take a look at the following examples that show the usage of Delete class methods.

delete.deleteColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
delete.deleteFamily(Bytes.toBytes("professional"));

Step 5: Delete the Data

Delete the selected data by passing the delete instance to the delete() method of the HTable class as shown below.

table.delete(delete); 

Step 6: Close the HTableInstance

After deleting the data, close the HTable Instance.

table.close();

Given below is the complete program to delete data from the HBase table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.util.Bytes;

public class DeleteData {

   public static void main(String[] args) throws IOException {

      // Instantiating Configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable table = new HTable(conf, "employee");

      // Instantiating Delete class
      Delete delete = new Delete(Bytes.toBytes("row1"));
      delete.deleteColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
      delete.deleteFamily(Bytes.toBytes("professional"));

      // deleting the data
      table.delete(delete);

      // closing the HTable object
      table.close();
      System.out.println("data deleted.....");
   }
}

Compile and execute the above program as shown below.

$javac Deletedata.java
$java DeleteData

The following should be the output:

data deleted