Optimize NULL Handling in Outer JOINs

Impact: MEDIUM

Set join_use_nulls = 0 to use default column values instead of NULL markers, reducing memory overhead compared to Nullable wrappers.

Example:

sql

-- Use default values instead of NULLs for non-matching rows
SET join_use_nulls = 0;

SELECT o.order_id, c.name
FROM orders o
LEFT JOIN customers c ON c.id = o.customer_id;
-- Non-matching rows get '' for name instead of NULL

When to use:

Setting	Behavior	Use Case
`join_use_nulls = 0`	Default values (empty string, 0) for non-matches	When you can handle default values
`join_use_nulls = 1` (default)	NULL for non-matches	When you need to distinguish "no match" from "matched with default"

Reference: Minimize and Optimize JOINs