Order of execution in a single SQL

execution_order.sql

UPDATE work_items set execution_order = (
	SELECT 
	(
		(
			SELECT execution_order
			FROM work_items
			WHERE id = '12262'
		)
	+
		(
			SELECT execution_order
			FROM work_items
			WHERE execution_order < (
				SELECT execution_order
				FROM work_items
				WHERE id = '12938'
			)
			ORDER BY execution_order DESC
			LIMIT 1
		)
	)
	/2
)
WHERE id = 12938;