How to Handle NULL Values in GROUP BY Clauses to Include All Rows?

GROUP BY Null Handling

When utilizing GROUP BY to aggregate data, it's crucial to consider how NULL values are handled. By default, NULL values are grouped together, potentially excluding rows with missing values.

In this scenario, you're grouping rows by the ancestor field and want to include rows where ancestor is NULL. To achieve this, you can leverage a workaround:

SELECT `table1`.*,
    IFNULL(ancestor, UUID()) AS `unq_ancestor`,
    GROUP_CONCAT(id SEPARATOR ',') AS `children_ids`
FROM `table1`
WHERE (enabled = 1)
GROUP BY `unq_ancestor`;

The UUID() function generates a unique identifier for each row with a NULL ancestor value. This ensures that rows with NULL ancestor are assigned a unique identifier, preventing them from being grouped together.

By replacing the ancestor field with unq_ancestor in the GROUP BY clause, the query will now group rows based on the unique identifier for NULL values, and all rows will be included in the result set.

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