複数の列のMAXエントリのGREATESTが存在する行のMySQLSELECTID

これを行う方法は、日付をユーザー定義変数に格納することです。次に、それを使用して最大の日付のIDを引き出すことができます

SET @A := (SELECT GREATEST(
                     IFNULL(max(date1), 0),
                     IFNULL(max(date2), 0),
                     IFNULL(max(date3), 0)
                  ) FROM table1
           );
-- here i JOIN a select that pulls out the correct id
SELECT t.joinid, max(`date1`), max(`date2`), max(`date3`)
FROM table1
JOIN 
(   SELECT id as joinid 
    FROM table1
    WHERE @A IN -- WHERE my MAX date is in
    (
        SELECT date1 -- here the UNION is just putting all of the dates into one column to compare one date with
        UNION ALL SELECT date2
        UNION ALL SELECT date3
    )
) t -- every table must have an alias

FIDDLEデモ