What is the difference between DELETE and truncate in Hive with examples

Introduction to Apache Hive:

Apache Hive is a data warehousing and SQL-like tool built on top of the Hadoop ecosystem. It facilitates easy data querying, analysis, and management of large-scale datasets using a familiar SQL-like syntax. When working with data in Hive, it's essential to understand the differences between various data manipulation commands, such as DELETE and TRUNCATE. In this beginner-friendly article, we'll explore the dissimilarities between these two commands, along with practical examples and clear explanations.

in earlier post we explained about How to Delete/Truncate Tables in Hadoop-Hive?

What is the Difference Between DELETE and TRUNCATE in Hive?

Both DELETE and TRUNCATE are used to remove data from Hive tables, but they function differently:

DELETE: The DELETE command is used to remove specific rows from a table based on a specified condition. It keeps the table structure intact and only removes the targeted rows, leaving other data unaffected.

TRUNCATE: The TRUNCATE command, on the other hand, removes all data from the table, effectively making it empty. Unlike DELETE, TRUNCATE does not consider any condition and quickly removes all rows from the table. It also retains the table structure, allowing it to be used immediately after truncation.

How to Truncate Data from a Hive External Table?

Truncating data from a Hive external table is done similarly to truncating a regular table:

Syntax for Truncating an External Table:

TRUNCATE TABLE external_table_name;

Example:

Let's assume we have an external table named "logs_external," which is mapped to data stored externally. To truncate this table, we execute the following Hive query:

Hive Query:

TRUNCATE TABLE logs_external;

Explanation:

The above Hive query will delete all data from the "logs_external" table, but it won't affect the external data files associated with it. The table structure will remain intact, allowing new data to be loaded into it.
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What is the TRUNCATE TABLE Command?

The TRUNCATE TABLE command is used to remove all data from a table while preserving the table's structure. It is an efficient way to quickly delete large amounts of data without impacting the table schema.

Can You Truncate a Table?

Yes, you can truncate a table in Hive. Truncating a table is a fast operation, especially when dealing with massive datasets, as it removes all rows without evaluating any conditions.

Why Use TRUNCATE Instead of DELETE?

There are several reasons to use TRUNCATE instead of DELETE:

Speed: TRUNCATE is faster than DELETE, as it removes all data at once, without checking conditions for each row.

Resource Efficiency: TRUNCATE consumes fewer resources, such as CPU and memory, compared to DELETE, making it more suitable for large-scale data removal.

Resetting Auto-Increment IDs: If your table has auto-increment IDs, DELETE won't reset them, but TRUNCATE will, making it easier to manage the table's primary keys.

What are Two Differences Between DELETE and TRUNCATE in Hive?

Difference 1: Operation

DELETE: Removes specific rows based on the condition specified in the query.

TRUNCATE: Removes all rows from the table, regardless of any condition.

Difference 2: Speed

DELETE: Slower than TRUNCATE, as it removes rows one by one, evaluating each condition.

TRUNCATE: Faster than DELETE, as it deletes all rows at once, without evaluating conditions.

Does TRUNCATE DELETE All Data?

Yes, TRUNCATE removes all data from the table, effectively making it empty, while preserving the table's structure.

Does TRUNCATE Remove All Rows?

Yes, TRUNCATE removes all rows from the table, leaving it empty.

Does TRUNCATE Remove Columns?

No, TRUNCATE does not remove columns. It only removes data from the table, leaving the table structure intact.

In Apache Hive, understanding the difference between DELETE and TRUNCATE is crucial for effective data management. While DELETE is used to remove specific rows based on conditions, TRUNCATE quickly clears all data from the table while keeping the structure unchanged. The choice between these commands depends on the use case and the desired outcome, making it essential to grasp their distinctions.