hive function round

Hive Function: ROUND

Introduction

When working with data in Hive, it is often necessary to manipulate and transform the data using various functions. One such function is the ROUND function, which allows you to round numeric values to a specified number of decimal places. In this article, we will explore the ROUND function in Hive and provide examples of how it can be used.

Syntax

The syntax for the ROUND function in Hive is as follows:

ROUND(number, decimal_places)

The number parameter is the numeric value that you want to round, and the decimal_places parameter is the number of decimal places to which you want to round the value. Both parameters are required.

Examples

Let's now look at some examples of how the ROUND function can be used in Hive.

Example 1: Basic Usage

Suppose we have a table sales with a column amount that contains sales amounts with decimal places. We want to round these amounts to 2 decimal places. We can achieve this using the ROUND function as shown below:

SELECT ROUND(amount, 2) AS rounded_amount
FROM sales;

This query will return a result set with the rounded sales amounts.

Example 2: Rounding Negative Numbers

The ROUND function in Hive follows the standard rounding rules. When rounding negative numbers, if the fractional part is exactly halfway between two integers, it rounds to the nearest even integer. Let's see an example:

SELECT ROUND(-1.5) AS rounded_value;

The result of this query will be -2 because -1.5 is exactly halfway between -1 and -2, and it rounds to the nearest even integer, which is -2.

Example 3: Rounding with Casting

In some cases, you may need to round a value and cast it to a different data type. The ROUND function can be used in conjunction with casting to achieve this. Here's an example:

SELECT CAST(ROUND(avg(sales), 2) AS INT) AS rounded_avg_sales
FROM sales_data;

In this query, we calculate the average of sales amounts in the sales_data table and round it to 2 decimal places. Then, we cast the result to an integer using the CAST function.

Sequence Diagram

The following sequence diagram illustrates the flow of execution when using the ROUND function in Hive:

sequenceDiagram
    participant User
    participant Hive
    participant HDFS
    
    User->>Hive: Submit SQL query with ROUND function
    Hive->>HDFS: Retrieve data from table
    HDFS-->>Hive: Provide data
    Hive->>Hive: Apply ROUND function on data
    Hive-->>User: Return result set with rounded values

The sequence diagram shows that the user submits a SQL query with the ROUND function to Hive. Hive retrieves the data from the underlying Hadoop Distributed File System (HDFS), applies the ROUND function on the data, and returns the result set to the user.

ER Diagram

The following ER diagram represents the relationship between the tables involved in the examples mentioned above:

erDiagram
    sales ||--|| sales_data : contains
    sales {
        int id
        decimal amount
    }
    sales_data {
        int id
        decimal sales
    }

The ER diagram shows that the sales table contains the amount column, which represents the sales amounts with decimal places. The sales_data table contains the sales column, which stores the sales amounts used in the casting example.

Conclusion

The ROUND function in Hive is a useful tool for rounding numeric values to a specified number of decimal places. It follows standard rounding rules and can be used in various scenarios, such as rounding sales amounts or calculating average values. By understanding the syntax and examples discussed in this article, you can confidently use the ROUND function in your Hive queries.