Hive ALTER TABLE ADD COLUMN

Introduction

Hive is a data warehouse infrastructure built on top of Hadoop. It provides tools to enable easy data summarization, ad-hoc querying, and analysis of large datasets. Hive uses a SQL-like query language called HiveQL to interact with data stored in Hadoop.

One of the most common operations in Hive is altering tables to add new columns. This allows users to modify the schema of existing tables without having to recreate them. In this article, we will explore how to use the ALTER TABLE ADD COLUMN statement in Hive and provide code examples to illustrate its usage.

Prerequisites

Before we dive into the details of altering tables in Hive, make sure you have the following prerequisites in place:

• A working installation of Hive
• A basic understanding of HiveQL
• Access to a Hive database and a table

ALTER TABLE ADD COLUMN Syntax

The ALTER TABLE ADD COLUMN statement in Hive allows you to add one or more columns to an existing table. The basic syntax of this statement is as follows:

ALTER TABLE table_name
ADD COLUMNS (column_name data_type [COMMENT column_comment], ...);

Here, table_name is the name of the table to which you want to add the column. column_name is the name of the column you want to add, and data_type is the data type of the column. Optionally, you can provide a comment for each column using the COMMENT keyword.

Examples

Let's consider a table named employees with the following schema:

Example 1: Adding a Single Column

Suppose we want to add a new column department of type string to the employees table. Here's how we can achieve that:

ALTER TABLE employees 
ADD COLUMNS (department string);

This will add the department column to the employees table.

Example 2: Adding Multiple Columns

If you need to add multiple columns to a table, you can do so by specifying them within the ADD COLUMNS clause. Let's say we want to add two columns address (string) and joining_date (date) to the employees table. Here's how you can accomplish that:

ALTER TABLE employees
ADD COLUMNS (address string, joining_date date);

This will add both the address and joining_date columns to the employees table.

Example 3: Adding Columns with Comments

You can also provide comments for the columns while adding them to the table. Let's say we want to add a column email of type string with a comment "Email address of the employee" to the employees table. Here's how you can achieve that:

ALTER TABLE employees
ADD COLUMNS (email string COMMENT 'Email address of the employee');

This will add the email column to the employees table with the specified comment.

Conclusion

In this article, we explored the ALTER TABLE ADD COLUMN statement in Hive. We learned about its syntax and saw examples of how to use it to add columns to existing tables. The ability to alter tables without recreating them is one of the key features of Hive, making it a flexible tool for data manipulation and analysis.

Remember to ensure you have the necessary prerequisites in place before using Hive and its ALTER TABLE statement. Practice using the examples provided to gain a better understanding of how to use this statement effectively.

Now that you have a good understanding of Hive's ALTER TABLE ADD COLUMN statement, you can confidently modify the schema of your Hive tables and adapt them to your evolving data requirements.

References:

• [Apache Hive Documentation](
• [Hive Language Manual - DDL](