How to Update Values in a Column in Hive

Hive, a popular analytics data warehouse built on top of Hadoop, is designed primarily for batch processing. Unlike traditional SQL databases where direct updating operations are available, Hive provides a workaround to update values in a column using a combination of INSERT OVERWRITE and the MERGE statement (available in Hive 2.0 and later).

Method 1: Using INSERT OVERWRITE

The INSERT OVERWRITE method involves creating a new table with updated values or overwriting the existing table and then renaming the table. This method is more straightforward and can be efficient for small to medium-sized datasets.

Step 1: Create a New Table or Overwrite the Existing Table

-- Step 1: Create a new table or overwrite the existing table CREATE TABLE new_table AS SELECT id, CASE WHEN condition THEN new_value ELSE old_value END AS column_to_update, other_columns FROM existing_table

Step 2: Optionally Drop the Old Table and Rename the New Table

-- Step 2: Optionally drop the old table and rename the new table DROP TABLE existing_table ALTER TABLE new_table RENAME TO existing_table

Method 2: Using MERGE Statement (Hive 2.0 and Later)

The MERGE statement in Hive allows you to update specific rows based on a condition. It enables more targeted updates and is more efficient for complex update scenarios.

MERGE Statement Syntax

MERGE INTO target_table AS t USING source_table AS s ON WHEN MATCHED THEN UPDATE SET _to_update _to_update WHEN NOT MATCHED THEN INSERT (id, column_to_update, other_columns) VALUES (, _to_update, s.other_columns)

Important Notes

Performance

These operations can be resource-intensive and may require significant time depending on the size of your dataset. Ensure you have sufficient computing resources available.

Transactional Tables

To use the MERGE statement, ensure your tables support ACID transactions. This is supported in Hive starting from version 1.2, and specifically for transactional tables (tables with the 'transactional' property set to 'true').

Backup

It's a good practice to back up your data before performing operations that modify it.

Minimum Requisites for Hive CRUD Using ACID Operations

To perform create, read, update, and delete (CRUD) operations using ACID transactions, the minimum requirements are:

Hive version 0.14 or later The file format must be in ORC file format with TBLPROPERTIES('transactional''true') The table must be CLUSTERED BY with some buckets

Note on Table Bucketing

If the table is not bucketed, you will get an error:

FAILED: SemanticException [Error 10297]: Attempt to do update or delete on table student2 that does not use an AcidOutputFormat or is not bucketed

New Configuration Parameters for Supporting Transactions in Hive 0.14

- true hive.enforce.bucketing - true - nonstrict hive.locking.enabled - true - 1

After setting these configurations, restart Hive or set them via terminal. For any Hadoop distributions, these properties are often enabled by default.

If you're looking for more in-depth discussions on similar topics, consider reading articles related to Hive transactions and ACID support.