Understanding Dynamic Date in Presto SQL

Introduction to Presto SQL and Date Functions

Presto SQL is an open-source, distributed SQL query engine that provides fast and scalable data processing capabilities. One of the key features of Presto SQL is its ability to handle complex date calculations and manipulations.

In this article, we will explore how to create a dynamic date column in Presto SQL using various techniques such as date functions, mathematical operations, and aggregations.

The Challenge: Creating Dynamic Date

The problem at hand involves creating a metric data check table that requires us to automate the “2021-04-30” date value every time we run the logic. We want to iterate through each month, starting from January 2021, and calculate the last day of each month.

Solution Overview

To solve this problem, we will use several Presto SQL functions and techniques, including:

• The last_day_of_month function to obtain the last day of each month
• Mathematical operations to subtract a fixed date from a variable date
• Aggregations using MAX and DATEPART
• Cross joins with CTEs (Common Table Expressions) for dynamic date manipulation

Step 1: Obtaining the Last Day of Each Month

We can start by creating a CTE called last_days_of_month that uses the UNNEST function to generate an array of months from January to December. Then, we use the last_day_of_month function to calculate the last day of each month.

WITH last_days_of_month AS (
    SELECT last_day_of_month(date('2021-' || cast(month as varchar) || '-01')) last_day
    FROM UNNEST(sequence(1,12)) t(month)
)

Step 2: Creating the Metric Data Check Table

Next, we create a CTE called metric that calculates the actual number of days for each country. We use the MAX function to get the maximum date partition and then subtract a fixed date (‘2020-01-01’) from it.

WITH metric AS (
    SELECT country
        , day(max(datepartition)- date '2020-01-01') AS actual_has_days
    FROM table
    GROUP BY 1
)

Step 3: Combining the CTEs for Dynamic Date

Finally, we combine the last_days_of_month and metric CTEs using a cross join to create the dynamic date values. We subtract the fixed date (‘2020-01-01’) from each last day of month to get the ideal days.

SELECT 
    last_day AS report_period 
    , country 
    , 'metric_a' AS metric_name 
    , CASE WHEN metric.actual_has_days = day_count.ideal_days THEN 'YES' ELSE 'NO' END AS data_passed
FROM metric
   CROSS JOIN (
        SELECT last_day, day(last_day - date '2020-01-01') AS ideal_days
        FROM last_days_of_month
   )

Step 4: Finalizing the Query

We can now combine all the CTEs to create the final dynamic date value query.

CREATE TABLE data_check_result AS 
    SELECT 
        last_day AS report_period 
        , country 
        , 'metric_a' AS metric_name 
        , CASE WHEN metric.actual_has_days = day_count.ideal_days THEN 'YES' ELSE 'NO' END AS data_passed
    FROM (
        WITH last_days_of_month AS (
            SELECT last_day_of_month(date('2021-' || cast(month as varchar) || '-01')) last_day
            FROM UNNEST(sequence(1,12)) t(month)
        ),
        metric AS (
            SELECT country
                , day(max(datepartition)- date '2020-01-01') AS actual_has_days
            FROM table
            GROUP BY 1
        )
    ) 
   AS subquery 
    CROSS JOIN (
        SELECT last_day, day(last_day - date '2020-01-01') AS ideal_days
        FROM last_days_of_month
   )

Conclusion

In this article, we have explored how to create a dynamic date column in Presto SQL using various techniques such as date functions, mathematical operations, and aggregations. We used CTEs (Common Table Expressions) for dynamic date manipulation and combined them with cross joins to achieve our goal.

This technique can be applied to various use cases where you need to manipulate dates dynamically, making it a powerful tool in your Presto SQL toolkit.

Last modified on 2024-12-31