How to Delete/Truncate Tables in Hadoop-Hive?

RB
2:47:37 PM
Hadoop-Hive is a powerful data warehousing and SQL-like tool in the Hadoop ecosystem, allowing users to manage and analyze large datasets. When dealing with vast amounts of data, it is crucial to understand how to remove tables properly to free up storage and resources. In this article, we will explore different methods to delete or truncate tables in Hive, along with relevant examples and Hive queries. earlier we explored 

Deleting a Table in Hive:

To delete a table permanently from Hive, you can use the "DROP TABLE" command. This action will remove the table and its associated data from the file system.

Syntax:
DROP TABLE [IF EXISTS] table_name;

Example:
Let's say we have a table named "employees," and we want to delete it from Hive.

Hive Query:
DROP TABLE employees;
Explanation:
Executing this Hive query will remove the "employees" table from Hive, including all its data. However, be cautious as this action is irreversible.

Deleting Data from a Table in Hive:

If you want to remove specific data from a table, you can use the "DELETE" command. This command is different from dropping a table, as it only removes rows while keeping the table structure intact.
Syntax:
DELETE FROM table_name [WHERE condition];
Example:
Consider the "sales" table with columns "product," "quantity," and "date." Suppose we want to delete rows where the quantity is zero.
Hive Query:
DELETE FROM sales WHERE quantity = 0;
Explanation:
This Hive query will delete all records from the "sales" table where the quantity is equal to zero.

Truncating a Table in Hive:

Truncating a table is a quick way to delete all data from the table while preserving the table structure. It is faster than deleting rows one by one.
Syntax:
TRUNCATE TABLE table_name;
Example:
Let's assume we have a table called "logs," and we want to remove all its data.
Hive Query:
TRUNCATE TABLE logs;
Explanation:

The above Hive query will remove all records from the "logs" table, making it empty while keeping the table's schema intact.

Dropping an External Table in Hive:

To drop an external table in Hive, you can use the same "DROP TABLE" command as used for regular tables.
Example:
Suppose we have an external table named "external_data," and we wish to delete it from Hive.
Hive Query:
    DROP TABLE external_data;

Explanation:
Executing this Hive query will delete the "external_data" table along with its metadata, but the data stored externally will remain untouched.

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In this article, we explored various methods to delete or truncate tables in Hadoop-Hive. We covered using "DROP TABLE" to delete tables, "DELETE" to remove specific data, and "TRUNCATE TABLE" to quickly delete all data while keeping the table structure. Additionally, we discussed dropping external tables. Remember to exercise caution while using these commands, as they can lead to irreversible data loss. Always make sure to have appropriate backups before performing any table modifications.