MySQL 5.7

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CREATE TABLE t(
    salesman INT NOT NULL AUTO_INCREMENT,
    sales INT,
    PRIMARY KEY (salesman),
    KEY (sales)
);
INSERT INTO t(sales)
SELECT FLOOR(RAND() * 1000000)
FROM (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) a
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) b
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) d
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) e
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) f
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) g
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) h
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) i
   , (SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL UNION ALL SELECT NULL) j;
(
    SELECT salesman, sales
    FROM t
    ORDER BY sales DESC
    LIMIT 3
)
UNION ALL
(
    SELECT 'Other', SUM(sales) - (
        SELECT SUM(sales)
        FROM (
            SELECT sales
            FROM t
            ORDER BY sales DESC
            LIMIT 3
        ) AS top3
    )
    FROM t
)
ORDER BY CASE WHEN salesman = 'Other' THEN NULL ELSE sales END DESC


salesman
sales


248010
999996

215855
999996

187825
999994

Other
130938773952


(
SELECT salesman, sales 
FROM t 
ORDER BY sales DESC
LIMIT 3
)
UNION
(
	SELECT 'Others', SUM(sales) 
	FROM (
		SELECT salesman, sales 
		FROM t 
		ORDER BY sales DESC LIMIT 3, 18446744073709551615
	) AS tt
);


salesman
sales


248010
999996

215855
999996

187825
999994

Others
130938773952