Updating Array Columns in Snowflake: A Deep Dive

In this article, we will explore how to update a key value in an array column in Snowflake. We’ll delve into the world of SQL, JSON, and array manipulation, providing a comprehensive guide for developers working with Snowflake.

Introduction to Arrays in Snowflake

Snowflake is a modern data warehousing platform that supports various data types, including arrays. An array is a collection of values of the same data type stored in a single column. In Snowflake, you can store multiple values in an array, which makes it ideal for storing hierarchical or recursive data.

Arrays are particularly useful when working with JSON data, as they provide a way to store and manipulate nested structures. In this article, we’ll focus on updating key values within array columns.

Understanding the Challenge

The question posed by the Stack Overflow user highlights a common challenge in working with arrays in Snowflake: updating key values for rows containing empty keys. The error message indicates that there’s an issue with the OBJECT_INSERT function, which is used to insert new elements into an array.

To overcome this challenge, we need to understand how Snowflake handles array operations and how to manipulate arrays using SQL.

Preparing for Array Operations

Before diving into the update statement, let’s take a closer look at the ARRAY_AGG function, which aggregates values from an array. This function is used in combination with the LATERAL FLATTEN operator to flatten nested JSON data into a flat array.

SELECT 
  ARRAY_AGG(
    CASE 
      WHEN json_data.value:dl_country::string = '' THEN OBJECT_INSERT(json_data.value, 'dl_country', src.dl_country)
      ELSE json_data.value
    END
  ) AS NEW_DETAILS_ARRAY
FROM tgt,
LATERAL FLATTEN(input =&gt; DETAILS_ARRAY) json_data,
(
  SELECT a_id, d_id, dl_country
  FROM doc_fix
  WHERE dl_country = ''
) src
WHERE tgt.a_id = src.a_id
AND tgt.d_id = src.d_id
GROUP BY a_id, d_id;

In this example, the ARRAY_AGG function aggregates values from the array using the CASE statement. If the value at the dl_country key is empty (''), it creates a new object with the updated value and adds it to the aggregated array.

Updating Array Columns

Now that we have an understanding of how arrays work in Snowflake, let’s move on to updating the array column. The provided SQL statement uses the UPDATE clause with a subquery to update the key values for rows containing empty keys.

UPDATE tgt
SET DETAILS_ARRAY = NEW_DETAILS_ARRAY
FROM (
  SELECT 
    a_id,
    d_id,
    ARRAY_AGG(
      CASE 
        WHEN json_data.value:dl_country::string = '' THEN OBJECT_INSERT(json_data.value, 'dl_country', src.dl_country)
        ELSE json_data.value
      END
    ) AS NEW_DETAILS_ARRAY
  FROM tgt,
  LATERAL FLATTEN(input =&gt; DETAILS_ARRAY) json_data,
  (
    SELECT a_id, d_id, dl_country
    FROM doc_fix
    WHERE dl_country = ''
  ) src
  WHERE tgt.a_id = src.a_id
  AND tgt.d_id = src.d_id
  GROUP BY a_id, d_id
) AS subquery
WHERE tgt.a_id = subquery.a_id
AND tgt.d_id = subquery.d_id;

This statement works as follows:

The outer UPDATE clause selects rows from the tgt table where the a_id and d_id match those in the src table.
The inner subquery uses the LATERAL FLATTEN operator to flatten the nested JSON data into a flat array using the ARRAY_AGG function.
The CASE statement within the aggregation function checks if the value at the dl_country key is empty (''). If it is, it creates a new object with the updated value and adds it to the aggregated array.
Finally, the outer UPDATE clause updates the DETAILS_ARRAY column in the tgt table using the new aggregated array.

Conclusion

Updating arrays in Snowflake requires an understanding of SQL, JSON, and array manipulation. By using the ARRAY_AGG function, LATERAL FLATTEN, and OBJECT_INSERT functions, you can update key values within array columns efficiently.

In this article, we’ve explored how to update array columns for rows containing empty keys in Snowflake. With this knowledge, you’ll be able to tackle complex data manipulation tasks with confidence.

References

Last modified on 2023-11-16