SELECT DISTINCT
    products.name AS name
FROM
    products
    LEFT JOIN (
        SELECT
            id_product
        FROM
            transactions
        WHERE
            CAST(transactions.date AS date) = '2019-06-01') AS SUBQ1 ON products.id_product = SUBQ1.id_product
WHERE
    SUBQ1.id_product IS NOT NULL
UNION
SELECT DISTINCT
    products.name AS name
FROM
    products
    LEFT JOIN (
        SELECT
            id_product
        FROM
            transactions
        WHERE
            CAST(transactions.date AS date) = '2019-06-08') AS SUBQ2 ON products.id_product = SUBQ2.id_product
WHERE
    SUBQ2.id_product IS NOT NULL;