MySQL 8.0

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CREATE TABLE sotrudniki
SELECT 'Коля' name UNION ALL
SELECT 'Петя' UNION ALL
SELECT 'Вася';
CREATE TABLE transport
SELECT 'Машина' nazvanie UNION ALL
SELECT 'Велосипед' UNION ALL
SELECT 'Трактор';

Records: 3  Duplicates: 0  Warnings: 0

Records: 3  Duplicates: 0  Warnings: 0

(SELECT DISTINCT name AS zagolovok FROM sotrudniki ORDER BY 1)
UNION ALL
(SELECT DISTINCT nazvanie FROM transport ORDER BY 1)

zagolovok

Коля

Петя

Вася

Машина

Велосипед

Трактор

-- LIMIT обязателен, иначе сортировка не выполнится.
-- Предел поставить побольше.
(SELECT DISTINCT name AS zagolovok FROM sotrudniki ORDER BY 1 LIMIT 2147483647)
UNION ALL
(SELECT DISTINCT nazvanie FROM transport ORDER BY 1 LIMIT 2147483647)

zagolovok

Вася

Коля

Петя

Велосипед

Машина

Трактор