如何使用 select 命令将 3 个不同表中的数据插入到一个表中答案

【问题标题】：how to insert data from 3 different tables into one table using the select command如何使用 select 命令将 3 个不同表中的数据插入到一个表中
【发布时间】：2020-05-14 09:29:56
【问题描述】：

这是我的桌子

eleve表

+----------------+-------------+------+-----+---------+-------+
| Field          | Type        | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+-------+
| idEleve        | int(11)     | NO   | PRI | NULL    |       |
| NomEleve       | varchar(30) | YES  |     | NULL    |       |
| PrenomEleve    | varchar(30) | YES  |     | NULL    |       |
| DateNaissEleve | date        | YES  |     | NULL    |       |
| LieuNaissEleve | varchar(30) | YES  |     | NULL    |       |
| codeClasse     | varchar(30) | YES  | MUL | NULL    |       |
+----------------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> select *from eleve ;
+---------+-----------+-------------+----------------+----------------+------------+
| idEleve | NomEleve  | PrenomEleve | DateNaissEleve | LieuNaissEleve | codeClasse |
+---------+-----------+-------------+----------------+----------------+------------+
|       1 | brahim    | elmoctar    | 1996-08-19     | teyaret        | CP1        |
|       2 | mohamed   | elmoctar    | 2000-02-01     | teyaret        | CP2        |
|       3 | fatimetou | elmoctar    | 1995-05-19     | teyaret        | CP3        |
+---------+-----------+-------------+----------------+----------------+------------+

note表

mysql> desc note ;
+-------------------+---------+------+-----+---------+-------+
| Field             | Type    | Null | Key | Default | Extra |
+-------------------+---------+------+-----+---------+-------+
| idAffectationProf | int(11) | YES  | MUL | NULL    |       |
| idEleve           | int(11) | YES  | MUL | NULL    |       |
| NoteTrimester1    | double  | YES  |     | NULL    |       |
| NoteTrimester2    | double  | YES  |     | NULL    |       |
| NoteTrimester3    | double  | YES  |     | NULL    |       |
+-------------------+---------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> select * from note ;
+-------------------+---------+----------------+----------------+----------------+
| idAffectationProf | idEleve | NoteTrimester1 | NoteTrimester2 | NoteTrimester3 |
+-------------------+---------+----------------+----------------+----------------+
|                 1 |       1 |          13.24 |          12.45 |          10.54 |
|                 2 |       1 |          10.24 |          17.45 |          18.54 |
|                 3 |       1 |          15.24 |          12.45 |          13.54 |
+-------------------+---------+----------------+----------------+----------------+
3 rows in set (0.00 sec)

affectationMatiere表

mysql> desc affectationMatiere ;
+-------------------+-------------+------+-----+---------+-------+
| Field             | Type        | Null | Key | Default | Extra |
+-------------------+-------------+------+-----+---------+-------+
| idAffectationProf | int(11)     | NO   | PRI | NULL    |       |
| codeClasse        | varchar(30) | YES  | MUL | NULL    |       |
| idProf            | int(11)     | YES  | MUL | NULL    |       |
| codeMat           | varchar(30) | YES  | MUL | NULL    |       |
| Annee             | date        | YES  |     | NULL    |       |
+-------------------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> select *from affectationMatiere ;
+-------------------+------------+--------+---------+------------+
| idAffectationProf | codeClasse | idProf | codeMat | Annee      |
+-------------------+------------+--------+---------+------------+
|                 1 | CP1        |      1 | Math    | 2020-01-01 |
|                 2 | CP2        |      2 | PC      | 2020-02-02 |
|                 3 | CP3        |      1 | SN      | 2020-03-03 |
+-------------------+------------+--------+---------+------------+
3 rows in set (0.00 sec)

moyenne表

mysql> desc moyenne ;
+---------------------+---------+------+-----+---------+-------+
| Field               | Type    | Null | Key | Default | Extra |
+---------------------+---------+------+-----+---------+-------+
| idEleve             | int(11) | YES  | MUL | NULL    |       |
| Annee               | date    | NO   | PRI | NULL    |       |
| moyenneGlobaleEleve | double  | YES  |     | NULL    |       |
+---------------------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)

我想在moyenne 表中插入idEleve、Annee 和每个学生的总平均数。

这是我的查询：

INSERT INTO moyenne 
    SELECT E.idEleve,a.Annee, (note.NoteTrimester1 + note.NoteTrimester2 + note.NoteTrimester3)/3 AS NoteGlobal FROM eleve E,affectMatiere a, note;

但不幸的是，请求返回 27 结果而不是 3。突然我在没有插入的情况下执行了请求，这就是我发现的

mysql> SELECT E.idEleve,a.Annee, (note.NoteTrimester1 + note.NoteTrimester2 + note.NoteTrimester3)/3 AS NoteGlobal FROM eleve E,affectationMatiere a, note;
+---------+------------+--------------------+
| idEleve | Annee      | NoteGlobal         |
+---------+------------+--------------------+
|       1 | 2020-01-01 | 12.076666666666666 |
|       2 | 2020-01-01 | 12.076666666666666 |
|       3 | 2020-01-01 | 12.076666666666666 |
|       1 | 2020-02-02 | 12.076666666666666 |
|       2 | 2020-02-02 | 12.076666666666666 |
|       3 | 2020-02-02 | 12.076666666666666 |
|       1 | 2020-03-03 | 12.076666666666666 |
|       2 | 2020-03-03 | 12.076666666666666 |
|       3 | 2020-03-03 | 12.076666666666666 |
|       1 | 2020-01-01 | 15.409999999999998 |
|       2 | 2020-01-01 | 15.409999999999998 |
|       3 | 2020-01-01 | 15.409999999999998 |
|       1 | 2020-02-02 | 15.409999999999998 |
|       2 | 2020-02-02 | 15.409999999999998 |
|       3 | 2020-02-02 | 15.409999999999998 |
|       1 | 2020-03-03 | 15.409999999999998 |
|       2 | 2020-03-03 | 15.409999999999998 |
|       3 | 2020-03-03 | 15.409999999999998 |
|       1 | 2020-01-01 | 13.743333333333332 |
|       2 | 2020-01-01 | 13.743333333333332 |
|       3 | 2020-01-01 | 13.743333333333332 |
|       1 | 2020-02-02 | 13.743333333333332 |
|       2 | 2020-02-02 | 13.743333333333332 |
|       3 | 2020-02-02 | 13.743333333333332 |
|       1 | 2020-03-03 | 13.743333333333332 |
|       2 | 2020-03-03 | 13.743333333333332 |
|       3 | 2020-03-03 | 13.743333333333332 |
+---------+------------+--------------------+
27 rows in set (0.00 sec)

【问题讨论】：

标签： mysql sql inner-join aggregate-functions sql-insert

【解决方案1】：

您现在构建了一个笛卡尔积，但实际上您想要加入条件。如果可能有学生尚未参加任何课程但也应该出现在结果中，那么您可能需要左连接。您还应该始终在INSERT 语句中记下目标列。

INSERT INTO moyenne
            (ideleve,
             annee,
             moyenneglobaleeleve)
SELECT e.ideleve,
       a.annee,
       (notetrimester1
        + notetrimester2
        + notetrimester3)
       / 3
       FROM eleve e
            LEFT JOIN note n
                      ON n.ideleve = e.ideleve
            LEFT JOIN affectationmatiere am
                      ON am.idaffectationorof = n.idaffectationprof;

【讨论】：

【解决方案2】：

您的查询的主要问题是您缺少表之间的连接条件：这会导致 3 个表之间的笛卡尔积。请注意，就问题而言，您不需要引入eleve 表来生成预期的结果集。

另外，我认为您需要聚合以收集所有 codeMats 中每个（eleve、annee）的注释。

我认为以下查询可以满足您的要求：

insert into moyenne 
select 
    n.idEleve,
    a.Annee, 
    avg(n.NoteTrimester1 + n.NoteTrimester2 + n.NoteTrimester3)/3 
from 
    note n
    inner join affectMatiere a on a.idAffectationProf = n.idAffectationProf
group by 
    n.idEleve,
    a.Annee

【讨论】：