如何只选择表中的最后一个条目？

Question

我有表 Matieres 和 Resultats

 ___ Matieres ___            ___ Resultats ___
    id (int auto increment)      ID (int auto_increment)
    Nom (varchar)            TIME_OF_INSERTION (datetime current_timestamp)
    Categorie (varchar)          ID_USER (int)
    Active (boolean)             ID_MATIERE (int)
                                 RESULTAT (int)

我有这个要求：

SELECT * FROM Matieres LEFT JOIN Resultats ON Matieres.id = Resultats.ID_MATIERE AND Resultats.ID_USER = :userid WHERE Active = TRUE AND ID_Formation = :formation)

问题在于，它会为每个 Matieres 返回用户在 Resultats 表中插入的每个结果。当我只想为每个Matieres.Nom 插入最后一个时...：/

我尝试使用GROUP BY TIME_OF_INSERTION ，但它不起作用:(

Answer 1

你可以使用row_number():

SELECT *
FROM Matieres m LEFT JOIN
     (SELECT r.*,
             ROW_NUMBER() OVER (PARTITION BY id_Matiere, id_user ORDER BY time_of_insertions DESC) as seqnum
      FROM Resultats r
      WHERE r.ID_USER = :userid 
     ) r
     ON m.id = r.ID_MATIERE AND
        seqnum = 1
WHERE Active = TRUE AND ID_Formation = :formation;

Answer 2

尝试在查询末尾添加index 1 以获取最后一条也是唯一一条记录