SELECT
    *
FROM
    (
SELECT
    horse_name AS Horse_Name,
    GROUP_CONCAT(
        placing_numerical
    ORDER BY
        race_date
    DESC SEPARATOR
        ', '
    ) Place
FROM
    results
GROUP BY
    Horse_Name

)tbl其中tbl.place像“%xyz%”
多亏了jacob，我现在对子查询有了更多的了解。

一种方法是使用子查询

select *
    from (
      SELECT horse_name AS Horse_Name,  
      GROUP_CONCAT( placing_numerical ORDER BY race_date DESC SEPARATOR ', ' ) Place
) tbl
    Where tbl.Place like '%xyz%'