Unveiling Hidden Insights: How to Group Records by NULL and NOT NULL in SQL

Using UNION ALL:

This approach utilizes two separate queries, each focusing on one specific group (NULL or NOT NULL). These queries are then combined using the UNION ALL operator, which merges the results without removing duplicates.

Example:

-- Select records with column "age" NOT NULL
SELECT *
FROM your_table
WHERE age IS NOT NULL
GROUP BY other_column;

UNION ALL

-- Select records with column "age" NULL
SELECT *
FROM your_table
WHERE age IS NULL
GROUP BY other_column;

This example first selects and groups records where the age column has a value (NOT NULL). It then uses UNION ALL to combine this result with another query that selects and groups records where the age column is explicitly NULL. Both queries group by the other_column for further analysis.

Conditional Aggregation (CASE WHEN):

This approach uses the CASE WHEN expression within the GROUP BY clause to categorize records based on the presence or absence of NULL values.

SELECT
    CASE WHEN age IS NULL THEN 'NULL' ELSE 'NOT NULL' END AS null_indicator,
    COUNT(*) AS record_count
FROM your_table
GROUP BY null_indicator, other_column;

Here, the CASE WHEN expression creates a new column named null_indicator. It assigns the value 'NULL' if the age column is NULL, otherwise it assigns 'NOT NULL'. The GROUP BY clause then groups the records by both the null_indicator and the other_column. This provides information on the number of records in each category (NULL and NOT NULL) for each group defined by the other_column.

Related Issues and Solutions:

• Performance: The UNION ALL approach might be slightly slower than the CASE WHEN approach for large datasets due to the execution of separate queries.
• Filtering: If you need to filter specific groups (NULL or NOT NULL), you can add additional WHERE clauses within each sub-query in the UNION ALL approach or filter based on the null_indicator in the CASE WHEN approach.