Dans cet article, nous découvrirons les requêtes multi-tables dans la base de données MySQL. Il a une certaine valeur de référence. Les amis dans le besoin peuvent s'y référer. J'espère qu'il sera utile à tout le monde.
Requête multi-tables
Les résultats de la requête proviennent de plusieurs tables, c'est-à-dire multi- requête de table
Sous-requête : les instructions de requête sont imbriquées dans des instructions SQL, avec des performances médiocres. Requête basée sur les résultats de la requête d'une certaine instruction
Requête Union : UNION
Jointure croisée : cartésienne. product
Jointure interne :
Jointure équivalente : laissez les champs entre les tables établir une relation de connexion avec « équivalence »
Jointure inégale : la requête de jointure inégale est un jugement inconditionnel si vous interrogez les champs dans plusieurs tables Data. , les données qu'il contient ne seront pas synchronisées, chacune affichera les siennes, sans aucune corrélation.
Jointure naturelle : supprime les colonnes en double et la jointure égale
Jointure externe :
Jointure externe gauche : FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col
Jointure externe droite : FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col
Auto-jointure : effectuer une requête de connexion entre cette table et cette table
Sous-requête
Sous-requêtes couramment utilisées dans les clauses WHERE
1 Utilisées pour comparer les sous-requêtes dans les expressions ; les sous-requêtes ne peuvent renvoyer qu'une seule valeur (requête pour les personnes plus âgées que l'âge moyen de la table s1)
.MariaDB [hellodb]> select * from s1 where age > (select avg(age) from s1); +-------+--------------+-------+-----+--------+---------+-----------+ | StuID | Name | phone | Age | Gender | ClassID | TeacherID | +-------+--------------+-------+-----+--------+---------+-----------+ | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | | 4 | Ding Dian | NULL | 32 | M | 4 | 4 | | 5 | Yu Yutong | NULL | 26 | M | 3 | 1 | | 6 | Shi Qing | NULL | 46 | M | 5 | NULL | | 13 | Tian Boguang | NULL | 33 | M | 2 | NULL | | 24 | Xu Xian | NULL | 27 | M | NULL | NULL | | 25 | Sun Dasheng | NULL | 100 | M | NULL | NULL | +-------+--------------+-------+-----+--------+---------+-----------+ 7 rows in set (0.01 sec)
2. Les résultats de la requête sont intégrés dans une autre table et la conversion décimale en entier sera arrondie
MariaDB [hellodb]> select avg(age) from s1 ; (查看s1表平均年龄) +----------+ | avg(age) | +----------+ | 25.0857 | +----------+ 1 row in set (0.00 sec) MariaDB [hellodb]> select * from teachers; （原来的表内容） +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [hellodb]> update teachers set age=(select avg(age) from s1); （插入查询结果的表内容，没有指定字段会改掉所有） Query OK, 4 rows affected (0.00 sec) Rows matched: 4 Changed: 4 Warnings: 0 MariaDB [hellodb]> select * from teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 25 | M | | 2 | Zhang Sanfeng | 25 | M | | 3 | Miejue Shitai | 25 | F | | 4 | Lin Chaoying | 25 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [hellodb]> update teachers set age=48 where tid=4; （把tid为4的age修改为48做下面实验用） Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> select * from teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 25 | M | | 2 | Zhang Sanfeng | 25 | M | | 3 | Miejue Shitai | 25 | F | | 4 | Lin Chaoying | 48 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [hellodb]> update teachers set age=(select avg(age) from s1) where tid=4; （指定tid为4的age字段修改） Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> select * from teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 25 | M | | 2 | Zhang Sanfeng | 25 | M | | 3 | Miejue Shitai | 25 | F | | 4 | Lin Chaoying | 25 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec)
Requête multi-table :
Utilisez une sous-boucle pour afficher le table s1 et afficher la table des enseignants Informations sur les personnes dont l'âge est supérieur à l'âge moyen de la table s1.
MariaDB [hellodb]> update teachers set age=45 where tid=1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> update teachers set age=94 where tid=2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> update teachers set age=77 where tid=3; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> select * from teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 25 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) （以上是把年龄修改回来做实验） MariaDB [hellodb]> select * from teachers where age > (select avg(age) from s1); （多表子循环查询平均年龄大于25的人） +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | +-----+---------------+-----+--------+ 3 rows in set (0.00 sec) MariaDB [hellodb]> update teachers set age=26 where tid=4; （修改一下最后一条的年龄为26） Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> select * from teachers where age > (select avg(age) from s1); （最后一条也大于25就显示出来了） +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec)
Requête Union
l'union fusionne deux tables verticalement et l'en-tête de la table provient du premier enregistrement de requête.
MariaDB [hellodb]> select * from teachers -> union -> select stuid,name,age,gender from s1; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | | 1 | Shi Zhongyu | 22 | M | | 2 | Shi Potian | 22 | M | | 3 | Xie Yanke | 53 | M | | 4 | Ding Dian | 32 | M | | 5 | Yu Yutong | 26 | M | | 6 | Shi Qing | 46 | M | | 7 | Xi Ren | 19 | F | | 8 | Lin Daiyu | 17 | F | | 9 | Ren Yingying | 20 | F | | 10 | Yue Lingshan | 19 | F | | 11 | Yuan Chengzhi | 23 | M | | 12 | Wen Qingqing | 19 | F | | 13 | Tian Boguang | 33 | M | | 14 | Lu Wushuang | 17 | F | | 15 | Duan Yu | 19 | M | | 16 | Xu Zhu | 21 | M | | 17 | Lin Chong | 25 | M | | 18 | Hua Rong | 23 | M | | 19 | Xue Baochai | 18 | F | | 20 | Diao Chan | 19 | F | | 21 | Huang Yueying | 22 | F | | 22 | Xiao Qiao | 20 | F | | 23 | Ma Chao | 23 | M | | 24 | Xu Xian | 27 | M | | 25 | Sun Dasheng | 100 | M | | 26 | xietingfeng | 23 | M | | 27 | liudehua | 18 | F | | 28 | mahuateng | 20 | M | | 29 | wuyanzu | 19 | M | | 30 | wuzetian | 21 | F | | 31 | Song Jiang | 18 | M | | 32 | Zhang Sanfeng | 18 | M | | 33 | Miejue Shitai | 18 | F | | 34 | Lin Chaoying | 18 | F | | 38 | abc | 20 | M | +-----+---------------+-----+--------+ 39 rows in set (0.00 sec) MariaDB [hellodb]> select tid as id ,name,age,gender from teachers union select stuid,name,age,gender from s1; (起个别名替换掉表头的tid并纵向合并两张表) +----+---------------+-----+--------+ | id | name | age | gender | +----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | | 1 | Shi Zhongyu | 22 | M | | 2 | Shi Potian | 22 | M | | 3 | Xie Yanke | 53 | M | | 4 | Ding Dian | 32 | M | | 5 | Yu Yutong | 26 | M | | 6 | Shi Qing | 46 | M | | 7 | Xi Ren | 19 | F | | 8 | Lin Daiyu | 17 | F | | 9 | Ren Yingying | 20 | F | | 10 | Yue Lingshan | 19 | F | | 11 | Yuan Chengzhi | 23 | M | | 12 | Wen Qingqing | 19 | F | | 13 | Tian Boguang | 33 | M | | 14 | Lu Wushuang | 17 | F | | 15 | Duan Yu | 19 | M | | 16 | Xu Zhu | 21 | M | | 17 | Lin Chong | 25 | M | | 18 | Hua Rong | 23 | M | | 19 | Xue Baochai | 18 | F | | 20 | Diao Chan | 19 | F | | 21 | Huang Yueying | 22 | F | | 22 | Xiao Qiao | 20 | F | | 23 | Ma Chao | 23 | M | | 24 | Xu Xian | 27 | M | | 25 | Sun Dasheng | 100 | M | | 26 | xietingfeng | 23 | M | | 27 | liudehua | 18 | F | | 28 | mahuateng | 20 | M | | 29 | wuyanzu | 19 | M | | 30 | wuzetian | 21 | F | | 31 | Song Jiang | 18 | M | | 32 | Zhang Sanfeng | 18 | M | | 33 | Miejue Shitai | 18 | F | | 34 | Lin Chaoying | 18 | F | | 38 | abc | 20 | M | +----+---------------+-----+--------+ 39 rows in set (0.00 sec)
Union se connecte à elle-même pour supprimer les doublons.
MariaDB [hellodb]> create table t2 select * from teachers; （先导一张表出来做实验不能有主键，所以只用了这种方法导了数据没有把主键导过来）
Query OK, 4 rows affected (0.01 sec)
Records: 4 Duplicates: 0 Warnings: 0
MariaDB [hellodb]> select * from t2;
+-----+---------------+-----+--------+
| TID | Name | Age | Gender |
+-----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 26 | F |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
MariaDB [hellodb]> desc t2;
+--------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+----------------------+------+-----+---------+-------+
| TID | smallint(5) unsigned | NO | | 0 | |
| Name | varchar(100) | NO | | NULL | |
| Age | tinyint(3) unsigned | NO | | NULL | |
| Gender | enum('F','M') | YES | | NULL | |
+--------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
（添加重复的行做实验）
MariaDB [hellodb]> insert into t2 set tid=4,name='linchaoying',age=26,gender='F'; （这条记录添加的只有name不一样少了个空格）
Query OK, 1 row affected (0.00 sec)
MariaDB [hellodb]> insert into t2 set tid=4,name='lin chaoying',age=26,gender='F'; （完全一样加了一行）
Query OK, 1 row affected (0.00 sec)
MariaDB [hellodb]> select * from t2;
+-----+---------------+-----+--------+
| TID | Name | Age | Gender |
+-----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 26 | F |
| 4 | linchaoying | 26 | F |
| 4 | lin chaoying | 26 | F |
+-----+---------------+-----+--------+
6 rows in set (0.00 sec)
MariaDB [hellodb]> select * from t2 union select * from t2; （用union过滤掉重复的行，少一个空格的那条记录过滤不了）
+-----+---------------+-----+--------+
| TID | Name | Age | Gender |
+-----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 26 | F |
| 4 | linchaoying | 26 | F |
+-----+---------------+-----+--------+
5 rows in set (0.00 sec)Utiliser tout pour joindre simplement deux tables sans déduplication
MariaDB [hellodb]> select * from t2 union all select * from t2; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | | 4 | linchaoying | 26 | F | | 4 | lin chaoying | 26 | F | | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 26 | F | | 4 | linchaoying | 26 | F | | 4 | lin chaoying | 26 | F | +-----+---------------+-----+--------+ 12 rows in set (0.00 sec)
Jointure croisée
两张表横向组合，类似于笛卡尔乘积。 （cross join）
Utiliser le croisement entre deux tables A join signifie que chaque ligne de cette table est combinée avec toutes les lignes d'une autre table pour former une nouvelle ligne.
MariaDB [hellodb]> select * from s1 cross join teachers; +-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | phone | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | 1 | Song Jiang | 25 | M | | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | 2 | Zhang Sanfeng | 25 | M | | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | 3 | Miejue Shitai | 25 | F | | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | 4 | Lin Chaoying | 25 | F | | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | 1 | Song Jiang | 25 | M | | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | 2 | Zhang Sanfeng | 25 | M | | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | 3 | Miejue Shitai | 25 | F | | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | 4 | Lin Chaoying | 25 | F | | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | 1 | Song Jiang | 25 | M | | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | 2 | Zhang Sanfeng | 25 | M | | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | 3 | Miejue Shitai | 25 | F | | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | 4 | Lin Chaoying | 25 | F | | 4 | Ding Dian | NULL | 32 | M | 4 | 4 | 1 | Song Jiang | 25 | M | | 4 | Ding Dian | NULL | 32 | M | 4 | 4 | 2 | Zhang Sanfeng | 25 | M | | 4 | Ding Dian | NULL | 32 | M | 4 | 4 | 3 | Miejue Shitai | 25 | F | | 4 | Ding Dian | NULL | 32 | M | 4 | 4 | 4 | Lin Chaoying | 25 | F | | 5 | Yu Yutong | NULL | 26 | M | 3 | 1 | 1 | Song Jiang | 25 | M | | 5 | Yu Yutong | NULL | 26 | M | 3 | 1 | 2 | Zhang Sanfeng | 25 | M | | 5 | Yu Yutong | NULL | 26 | M | 3 | 1 | 3 | Miejue Shitai | 25 | F | | 5 | Yu Yutong | NULL | 26 | M | 3 | 1 | 4 | Lin Chaoying | 25 | F | | 6 | Shi Qing | NULL | 46 | M | 5 | NULL | 1 | Song Jiang | 25 | M | | 6 | Shi Qing | NULL | 46 | M | 5 | NULL | 2 | Zhang Sanfeng | 25 | M | | 6 | Shi Qing | NULL | 46 | M | 5 | NULL | 3 | Miejue Shitai | 25 | F | | 6 | Shi Qing | NULL | 46 | M | 5 | NULL | 4 | Lin Chaoying | 25 | F | | 7 | Xi Ren | NULL | 19 | F | 3 | NULL | 1 | Song Jiang | 25 | M | | 7 | Xi Ren | NULL | 19 | F | 3 | NULL | 2 | Zhang Sanfeng | 25 | M | | 7 | Xi Ren | NULL | 19 | F | 3 | NULL | 3 | Miejue Shitai | 25 | F | | 7 | Xi Ren | NULL | 19 | F | 3 | NULL | 4 | Lin Chaoying | 25 | F | | 8 | Lin Daiyu | NULL | 17 | F | 7 | NULL | 1 | Song Jiang | 25 | M | | 8 | Lin Daiyu | NULL | 17 | F | 7 | NULL | 2 | Zhang Sanfeng | 25 | M | | 8 | Lin Daiyu | NULL | 17 | F | 7 | NULL | 3 | Miejue Shitai | 25 | F | | 8 | Lin Daiyu | NULL | 17 | F | 7 | NULL | 4 | Lin Chaoying | 25 | F | | 9 | Ren Yingying | NULL | 20 | F | 6 | NULL | 1 | Song Jiang | 25 | M | | 9 | Ren Yingying | NULL | 20 | F | 6 | NULL | 2 | Zhang Sanfeng | 25 | M | | 9 | Ren Yingying | NULL | 20 | F | 6 | NULL | 3 | Miejue Shitai | 25 | F | | 9 | Ren Yingying | NULL | 20 | F | 6 | NULL | 4 | Lin Chaoying | 25 | F | | 10 | Yue Lingshan | NULL | 19 | F | 3 | NULL | 1 | Song Jiang | 25 | M | | 10 | Yue Lingshan | NULL | 19 | F | 3 | NULL | 2 | Zhang Sanfeng | 25 | M | | 10 | Yue Lingshan | NULL | 19 | F | 3 | NULL | 3 | Miejue Shitai | 25 | F | | 10 | Yue Lingshan | NULL | 19 | F | 3 | NULL | 4 | Lin Chaoying | 25 | F | | 11 | Yuan Chengzhi | NULL | 23 | M | 6 | NULL | 1 | Song Jiang | 25 | M | | 11 | Yuan Chengzhi | NULL | 23 | M | 6 | NULL | 2 | Zhang Sanfeng | 25 | M | | 11 | Yuan Chengzhi | NULL | 23 | M | 6 | NULL | 3 | Miejue Shitai | 25 | F | | 11 | Yuan Chengzhi | NULL | 23 | M | 6 | NULL | 4 | Lin Chaoying | 25 | F | | 12 | Wen Qingqing | NULL | 19 | F | 1 | NULL | 1 | Song Jiang | 25 | M | | 12 | Wen Qingqing | NULL | 19 | F | 1 | NULL | 2 | Zhang Sanfeng | 25 | M | | 12 | Wen Qingqing | NULL | 19 | F | 1 | NULL | 3 | Miejue Shitai | 25 | F | | 12 | Wen Qingqing | NULL | 19 | F | 1 | NULL | 4 | Lin Chaoying | 25 | F | | 13 | Tian Boguang | NULL | 33 | M | 2 | NULL | 1 | Song Jiang | 25 | M | | 13 | Tian Boguang | NULL | 33 | M | 2 | NULL | 2 | Zhang Sanfeng | 25 | M | | 13 | Tian Boguang | NULL | 33 | M | 2 | NULL | 3 | Miejue Shitai | 25 | F | | 13 | Tian Boguang | NULL | 33 | M | 2 | NULL | 4 | Lin Chaoying | 25 | F | | 14 | Lu Wushuang | NULL | 17 | F | 3 | NULL | 1 | Song Jiang | 25 | M | | 14 | Lu Wushuang | NULL | 17 | F | 3 | NULL | 2 | Zhang Sanfeng | 25 | M | | 14 | Lu Wushuang | NULL | 17 | F | 3 | NULL | 3 | Miejue Shitai | 25 | F | | 14 | Lu Wushuang | NULL | 17 | F | 3 | NULL | 4 | Lin Chaoying | 25 | F | | 15 | Duan Yu | NULL | 19 | M | 4 | NULL | 1 | Song Jiang | 25 | M | | 15 | Duan Yu | NULL | 19 | M | 4 | NULL | 2 | Zhang Sanfeng | 25 | M | | 15 | Duan Yu | NULL | 19 | M | 4 | NULL | 3 | Miejue Shitai | 25 | F | | 15 | Duan Yu | NULL | 19 | M | 4 | NULL | 4 | Lin Chaoying | 25 | F | | 16 | Xu Zhu | NULL | 21 | M | 1 | NULL | 1 | Song Jiang | 25 | M | | 16 | Xu Zhu | NULL | 21 | M | 1 | NULL | 2 | Zhang Sanfeng | 25 | M | | 16 | Xu Zhu | NULL | 21 | M | 1 | NULL | 3 | Miejue Shitai | 25 | F | | 16 | Xu Zhu | NULL | 21 | M | 1 | NULL | 4 | Lin Chaoying | 25 | F | | 17 | Lin Chong | NULL | 25 | M | 4 | NULL | 1 | Song Jiang | 25 | M | | 17 | Lin Chong | NULL | 25 | M | 4 | NULL | 2 | Zhang Sanfeng | 25 | M | | 17 | Lin Chong | NULL | 25 | M | 4 | NULL | 3 | Miejue Shitai | 25 | F | | 17 | Lin Chong | NULL | 25 | M | 4 | NULL | 4 | Lin Chaoying | 25 | F | | 18 | Hua Rong | NULL | 23 | M | 7 | NULL | 1 | Song Jiang | 25 | M | | 18 | Hua Rong | NULL | 23 | M | 7 | NULL | 2 | Zhang Sanfeng | 25 | M | | 18 | Hua Rong | NULL | 23 | M | 7 | NULL | 3 | Miejue Shitai | 25 | F | | 18 | Hua Rong | NULL | 23 | M | 7 | NULL | 4 | Lin Chaoying | 25 | F | | 19 | Xue Baochai | NULL | 18 | F | 6 | NULL | 1 | Song Jiang | 25 | M | | 19 | Xue Baochai | NULL | 18 | F | 6 | NULL | 2 | Zhang Sanfeng | 25 | M | | 19 | Xue Baochai | NULL | 18 | F | 6 | NULL | 3 | Miejue Shitai | 25 | F | | 19 | Xue Baochai | NULL | 18 | F | 6 | NULL | 4 | Lin Chaoying | 25 | F | | 20 | Diao Chan | NULL | 19 | F | 7 | NULL | 1 | Song Jiang | 25 | M | | 20 | Diao Chan | NULL | 19 | F | 7 | NULL | 2 | Zhang Sanfeng | 25 | M | | 20 | Diao Chan | NULL | 19 | F | 7 | NULL | 3 | Miejue Shitai | 25 | F | | 20 | Diao Chan | NULL | 19 | F | 7 | NULL | 4 | Lin Chaoying | 25 | F | | 21 | Huang Yueying | NULL | 22 | F | 6 | NULL | 1 | Song Jiang | 25 | M | | 21 | Huang Yueying | NULL | 22 | F | 6 | NULL | 2 | Zhang Sanfeng | 25 | M | | 21 | Huang Yueying | NULL | 22 | F | 6 | NULL | 3 | Miejue Shitai | 25 | F | | 21 | Huang Yueying | NULL | 22 | F | 6 | NULL | 4 | Lin Chaoying | 25 | F | | 22 | Xiao Qiao | NULL | 20 | F | 1 | NULL | 1 | Song Jiang | 25 | M | | 22 | Xiao Qiao | NULL | 20 | F | 1 | NULL | 2 | Zhang Sanfeng | 25 | M | | 22 | Xiao Qiao | NULL | 20 | F | 1 | NULL | 3 | Miejue Shitai | 25 | F | | 22 | Xiao Qiao | NULL | 20 | F | 1 | NULL | 4 | Lin Chaoying | 25 | F | | 23 | Ma Chao | NULL | 23 | M | 4 | NULL | 1 | Song Jiang | 25 | M | | 23 | Ma Chao | NULL | 23 | M | 4 | NULL | 2 | Zhang Sanfeng | 25 | M | | 23 | Ma Chao | NULL | 23 | M | 4 | NULL | 3 | Miejue Shitai | 25 | F | | 23 | Ma Chao | NULL | 23 | M | 4 | NULL | 4 | Lin Chaoying | 25 | F | | 24 | Xu Xian | NULL | 27 | M | NULL | NULL | 1 | Song Jiang | 25 | M | | 24 | Xu Xian | NULL | 27 | M | NULL | NULL | 2 | Zhang Sanfeng | 25 | M | | 24 | Xu Xian | NULL | 27 | M | NULL | NULL | 3 | Miejue Shitai | 25 | F | | 24 | Xu Xian | NULL | 27 | M | NULL | NULL | 4 | Lin Chaoying | 25 | F | | 25 | Sun Dasheng | NULL | 100 | M | NULL | NULL | 1 | Song Jiang | 25 | M | | 25 | Sun Dasheng | NULL | 100 | M | NULL | NULL | 2 | Zhang Sanfeng | 25 | M | | 25 | Sun Dasheng | NULL | 100 | M | NULL | NULL | 3 | Miejue Shitai | 25 | F | | 25 | Sun Dasheng | NULL | 100 | M | NULL | NULL | 4 | Lin Chaoying | 25 | F | | 26 | xietingfeng | NULL | 23 | M | 2 | 1 | 1 | Song Jiang | 25 | M | | 26 | xietingfeng | NULL | 23 | M | 2 | 1 | 2 | Zhang Sanfeng | 25 | M | | 26 | xietingfeng | NULL | 23 | M | 2 | 1 | 3 | Miejue Shitai | 25 | F | | 26 | xietingfeng | NULL | 23 | M | 2 | 1 | 4 | Lin Chaoying | 25 | F | | 27 | liudehua | NULL | 18 | F | 1 | NULL | 1 | Song Jiang | 25 | M | | 27 | liudehua | NULL | 18 | F | 1 | NULL | 2 | Zhang Sanfeng | 25 | M | | 27 | liudehua | NULL | 18 | F | 1 | NULL | 3 | Miejue Shitai | 25 | F | | 27 | liudehua | NULL | 18 | F | 1 | NULL | 4 | Lin Chaoying | 25 | F | | 28 | mahuateng | NULL | 20 | M | 3 | NULL | 1 | Song Jiang | 25 | M | | 28 | mahuateng | NULL | 20 | M | 3 | NULL | 2 | Zhang Sanfeng | 25 | M | | 28 | mahuateng | NULL | 20 | M | 3 | NULL | 3 | Miejue Shitai | 25 | F | | 28 | mahuateng | NULL | 20 | M | 3 | NULL | 4 | Lin Chaoying | 25 | F | | 29 | wuyanzu | NULL | 19 | M | 4 | NULL | 1 | Song Jiang | 25 | M | | 29 | wuyanzu | NULL | 19 | M | 4 | NULL | 2 | Zhang Sanfeng | 25 | M | | 29 | wuyanzu | NULL | 19 | M | 4 | NULL | 3 | Miejue Shitai | 25 | F | | 29 | wuyanzu | NULL | 19 | M | 4 | NULL | 4 | Lin Chaoying | 25 | F | | 30 | wuzetian | NULL | 21 | F | NULL | NULL | 1 | Song Jiang | 25 | M | | 30 | wuzetian | NULL | 21 | F | NULL | NULL | 2 | Zhang Sanfeng | 25 | M | | 30 | wuzetian | NULL | 21 | F | NULL | NULL | 3 | Miejue Shitai | 25 | F | | 30 | wuzetian | NULL | 21 | F | NULL | NULL | 4 | Lin Chaoying | 25 | F | | 31 | Song Jiang | NULL | 18 | M | 45 | NULL | 1 | Song Jiang | 25 | M | | 31 | Song Jiang | NULL | 18 | M | 45 | NULL | 2 | Zhang Sanfeng | 25 | M | | 31 | Song Jiang | NULL | 18 | M | 45 | NULL | 3 | Miejue Shitai | 25 | F | | 31 | Song Jiang | NULL | 18 | M | 45 | NULL | 4 | Lin Chaoying | 25 | F | | 32 | Zhang Sanfeng | NULL | 18 | M | 94 | NULL | 1 | Song Jiang | 25 | M | | 32 | Zhang Sanfeng | NULL | 18 | M | 94 | NULL | 2 | Zhang Sanfeng | 25 | M | | 32 | Zhang Sanfeng | NULL | 18 | M | 94 | NULL | 3 | Miejue Shitai | 25 | F | | 32 | Zhang Sanfeng | NULL | 18 | M | 94 | NULL | 4 | Lin Chaoying | 25 | F | | 33 | Miejue Shitai | NULL | 18 | F | 77 | NULL | 1 | Song Jiang | 25 | M | | 33 | Miejue Shitai | NULL | 18 | F | 77 | NULL | 2 | Zhang Sanfeng | 25 | M | | 33 | Miejue Shitai | NULL | 18 | F | 77 | NULL | 3 | Miejue Shitai | 25 | F | | 33 | Miejue Shitai | NULL | 18 | F | 77 | NULL | 4 | Lin Chaoying | 25 | F | | 34 | Lin Chaoying | NULL | 18 | F | 93 | NULL | 1 | Song Jiang | 25 | M | | 34 | Lin Chaoying | NULL | 18 | F | 93 | NULL | 2 | Zhang Sanfeng | 25 | M | | 34 | Lin Chaoying | NULL | 18 | F | 93 | NULL | 3 | Miejue Shitai | 25 | F | | 34 | Lin Chaoying | NULL | 18 | F | 93 | NULL | 4 | Lin Chaoying | 25 | F | | 38 | abc | NULL | 20 | M | NULL | NULL | 1 | Song Jiang | 25 | M | | 38 | abc | NULL | 20 | M | NULL | NULL | 2 | Zhang Sanfeng | 25 | M | | 38 | abc | NULL | 20 | M | NULL | NULL | 3 | Miejue Shitai | 25 | F | | 38 | abc | NULL | 20 | M | NULL | NULL | 4 | Lin Chaoying | 25 | F | +-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 140 rows in set (0.00 sec) 第一张表 0 1 2 3 1 2 3 4 第二张表 1 3 4 5 2 3 4 5 交叉连接后结果： 0 1 2 3 1 3 4 5 0 1 2 3 2 3 4 5 1 2 3 4 1 3 4 5 1 2 3 4 2 3 4 5 两张表换下位置不影响数据只是显示效果变了而已: 1 3 4 5 0 1 2 3 1 3 4 5 1 2 3 4 2 3 4 5 0 1 2 3 2 3 4 5 1 2 3 4 MariaDB [hellodb]> select * from teachers , s1; （这个命令也可以交叉连接但是比较老了推荐使用第一种） +-----+---------------+-----+--------+-------+---------------+-------+-----+--------+---------+-----------+ | TID | Name | Age | Gender | StuID | Name | phone | Age | Gender | ClassID | TeacherID | +-----+---------------+-----+--------+-------+---------------+-------+-----+--------+---------+-----------+ | 1 | Song Jiang | 25 | M | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | | 2 | Zhang Sanfeng | 25 | M | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | | 3 | Miejue Shitai | 25 | F | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | | 4 | Lin Chaoying | 25 | F | 1 | Shi Zhongyu | NULL | 22 | M | 2 | 3 | | 1 | Song Jiang | 25 | M | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | | 2 | Zhang Sanfeng | 25 | M | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | | 3 | Miejue Shitai | 25 | F | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | | 4 | Lin Chaoying | 25 | F | 2 | Shi Potian | NULL | 22 | M | 1 | 7 | | 1 | Song Jiang | 25 | M | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | | 2 | Zhang Sanfeng | 25 | M | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | | 3 | Miejue Shitai | 25 | F | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 | | 4 | Lin Chaoying | 25 | F | 3 | Xie Yanke | NULL | 53 | M | 2 | 16 |
Sélectionnez des champs individuels dans les deux tables.
MariaDB [hellodb]> select name,age,gender from teachers cross join s1; (这里有两个字段是重复的name，age两个表都有) ERROR 1052 (23000): Column 'name' in field list is ambiguous MariaDB [hellodb]> select stuid,s1.name,tid,teachers.name from teachers cross join s1; （分别指定是哪个表的name） +-------+---------------+-----+---------------+ | stuid | name | tid | name | +-------+---------------+-----+---------------+ | 1 | Shi Zhongyu | 1 | Song Jiang | | 1 | Shi Zhongyu | 2 | Zhang Sanfeng | | 1 | Shi Zhongyu | 3 | Miejue Shitai | | 1 | Shi Zhongyu | 4 | Lin Chaoying | | 2 | Shi Potian | 1 | Song Jiang | | 2 | Shi Potian | 2 | Zhang Sanfeng | | 2 | Shi Potian | 3 | Miejue Shitai | | 2 | Shi Potian | 4 | Lin Chaoying | | 3 | Xie Yanke | 1 | Song Jiang | | 3 | Xie Yanke | 2 | Zhang Sanfeng | | 3 | Xie Yanke | 3 | Miejue Shitai | | 3 | Xie Yanke | 4 | Lin Chaoying | | 4 | Ding Dian | 1 | Song Jiang | | 4 | Ding Dian | 2 | Zhang Sanfeng | | 4 | Ding Dian | 3 | Miejue Shitai | | 4 | Ding Dian | 4 | Lin Chaoying | | 5 | Yu Yutong | 1 | Song Jiang | | 5 | Yu Yutong | 2 | Zhang Sanfeng | | 5 | Yu Yutong | 3 | Miejue Shitai | | 5 | Yu Yutong | 4 | Lin Chaoying | | 6 | Shi Qing | 1 | Song Jiang | | 6 | Shi Qing | 2 | Zhang Sanfeng | | 6 | Shi Qing | 3 | Miejue Shitai | | 6 | Shi Qing | 4 | Lin Chaoying | | 7 | Xi Ren | 1 | Song Jiang | | 7 | Xi Ren | 2 | Zhang Sanfeng | | 7 | Xi Ren | 3 | Miejue Shitai | | 7 | Xi Ren | 4 | Lin Chaoying | | 8 | Lin Daiyu | 1 | Song Jiang | | 8 | Lin Daiyu | 2 | Zhang Sanfeng | | 8 | Lin Daiyu | 3 | Miejue Shitai | | 8 | Lin Daiyu | 4 | Lin Chaoying | | 9 | Ren Yingying | 1 | Song Jiang | | 9 | Ren Yingying | 2 | Zhang Sanfeng | | 9 | Ren Yingying | 3 | Miejue Shitai | | 9 | Ren Yingying | 4 | Lin Chaoying | | 10 | Yue Lingshan | 1 | Song Jiang | | 10 | Yue Lingshan | 2 | Zhang Sanfeng | | 10 | Yue Lingshan | 3 | Miejue Shitai | | 10 | Yue Lingshan | 4 | Lin Chaoying | | 11 | Yuan Chengzhi | 1 | Song Jiang | | 11 | Yuan Chengzhi | 2 | Zhang Sanfeng | | 11 | Yuan Chengzhi | 3 | Miejue Shitai | | 11 | Yuan Chengzhi | 4 | Lin Chaoying | （省略了太长） MariaDB [hellodb]> select stuid,s1.name,s1.age,tid,teachers.name,teachers.age from teachers cross join s1; （name和age都可以加在里面指定） +-------+---------------+-----+-----+---------------+-----+ | stuid | name | age | tid | name | age | +-------+---------------+-----+-----+---------------+-----+ | 1 | Shi Zhongyu | 22 | 1 | Song Jiang | 25 | | 1 | Shi Zhongyu | 22 | 2 | Zhang Sanfeng | 25 | | 1 | Shi Zhongyu | 22 | 3 | Miejue Shitai | 25 | | 1 | Shi Zhongyu | 22 | 4 | Lin Chaoying | 25 | | 2 | Shi Potian | 22 | 1 | Song Jiang | 25 | | 2 | Shi Potian | 22 | 2 | Zhang Sanfeng | 25 | | 2 | Shi Potian | 22 | 3 | Miejue Shitai | 25 | | 2 | Shi Potian | 22 | 4 | Lin Chaoying | 25 | | 3 | Xie Yanke | 53 | 1 | Song Jiang | 25 | | 3 | Xie Yanke | 53 | 2 | Zhang Sanfeng | 25 | | 3 | Xie Yanke | 53 | 3 | Miejue Shitai | 25 | | 3 | Xie Yanke | 53 | 4 | Lin Chaoying | 25 | | 4 | Ding Dian | 32 | 1 | Song Jiang | 25 | | 4 | Ding Dian | 32 | 2 | Zhang Sanfeng | 25 | | 4 | Ding Dian | 32 | 3 | Miejue Shitai | 25 | | 4 | Ding Dian | 32 | 4 | Lin Chaoying | 25 | | 5 | Yu Yutong | 26 | 1 | Song Jiang | 25 | | 5 | Yu Yutong | 26 | 2 | Zhang Sanfeng | 25 | | 5 | Yu Yutong | 26 | 3 | Miejue Shitai | 25 | | 5 | Yu Yutong | 26 | 4 | Lin Chaoying | 25 | （省略了太长） MariaDB [hellodb]> select stuid,s1.name as s1_name,tid,teachers.name as teachers_name from teachers cross join s1; (也可以加上别名来区分比较清晰) +-------+---------------+-----+---------------+ | stuid | s1_name | tid | teachers_name | +-------+---------------+-----+---------------+ | 1 | Shi Zhongyu | 1 | Song Jiang | | 1 | Shi Zhongyu | 2 | Zhang Sanfeng | | 1 | Shi Zhongyu | 3 | Miejue Shitai | | 1 | Shi Zhongyu | 4 | Lin Chaoying | | 2 | Shi Potian | 1 | Song Jiang | | 2 | Shi Potian | 2 | Zhang Sanfeng | | 2 | Shi Potian | 3 | Miejue Shitai | | 2 | Shi Potian | 4 | Lin Chaoying | | 3 | Xie Yanke | 1 | Song Jiang | | 3 | Xie Yanke | 2 | Zhang Sanfeng | | 3 | Xie Yanke | 3 | Miejue Shitai | | 3 | Xie Yanke | 4 | Lin Chaoying | （省略）
MariaDB [hellodb]> select stuid,s.name as s1_name,s.age,t.name as teachers_name,t.age from teachers t cross join s1 s; +-------+---------------+-----+---------------+-----+ | stuid | s1_name | age | teachers_name | age | +-------+---------------+-----+---------------+-----+ | 1 | Shi Zhongyu | 22 | Song Jiang | 25 | | 1 | Shi Zhongyu | 22 | Zhang Sanfeng | 25 | | 1 | Shi Zhongyu | 22 | Miejue Shitai | 25 | | 1 | Shi Zhongyu | 22 | Lin Chaoying | 25 | | 2 | Shi Potian | 22 | Song Jiang | 25 | | 2 | Shi Potian | 22 | Zhang Sanfeng | 25 | | 2 | Shi Potian | 22 | Miejue Shitai | 25 | | 2 | Shi Potian | 22 | Lin Chaoying | 25 | | 3 | Xie Yanke | 53 | Song Jiang | 25 | | 3 | Xie Yanke | 53 | Zhang Sanfeng | 25 | | 3 | Xie Yanke | 53 | Miejue Shitai | 25 | | 3 | Xie Yanke | 53 | Lin Chaoying | 25 | | 4 | Ding Dian | 32 | Song Jiang | 25 | | 4 | Ding Dian | 32 | Zhang Sanfeng | 25 | | 4 | Ding Dian | 32 | Miejue Shitai | 25 | | 4 | Ding Dian | 32 | Lin Chaoying | 25 | MariaDB [hellodb]> select stuid,s1.name s1_name,s1.age,tid,t.name teacher_name,teachers.age from teachers t cross join s1; （别名定义之后不能使用原始名字） ERROR 1054 (42S22): Unknown column 'teachers.age' in 'field list'
Filtre après jointure interne : connectez-vous d'abord puis filtrez, affichez les personnes dont la table s1 est supérieure à 30. 等值连接：让表之间的字段以“等值”建立连接关系
MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid; （三个个老师各教一个学生） +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 3 rows in set (0.00 sec) MariaDB [hellodb]> update s1 set teacherid=1 where stuid=25; （修改一下s1表的teacherid的值为1） Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid; （再次使用这条命令，查看就是songjiang教两个学生） +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [hellodb]> select * from s1 , t1 where s1.teacherid=t1.tid; (不加 inner join 的老写法) +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 4 rows in set (0.01 sec)
Jointure externe :
Gauche jointure externe : FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col (classé à l'avant)Jointure externe droite : FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col (classé à l'arrière) Rejoindre l'extérieur gauche à l'extérieur gauche
La table entière des étudiants est conservée, seule celle du professeur est laissée là où il y a une intersection. (Remplacer par des valeurs nulles là où il n'y a pas d'intersection)Utilisation de l'expansion de la jointure externe gaucheMariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid and s1.age >30; +-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+ | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+ 2 rows in set (0.00 sec)Copier après la connexion
MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid where s1.a +-------+-------------+-----+--------+---------+-----------+-----+--------------+-- | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | A +-------+-------------+-----+--------+---------+-----------+-----+--------------+-- | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | +-------+-------------+-----+--------+---------+-----------+-----+--------------+-- 2 rows in set (0.00 sec)
Lien extérieur droit : extérieur droit
MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid; +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ 25 rows in set (0.00 sec)
MariaDB [hellodb]> select * from t1; （教师表） +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid where tid is null; （前面两个，老师表里没有这两个老师的编号） +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ 21 rows in set (0.00 sec)
Jointure externe complète
MariaDB [hellodb]> select * from s1 right outer join t1 on s1.teacherid=t1.tid; +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ 5 rows in set (0.00 sec)
MariaDB [hellodb]> select * from s1 right outer join t1 on s1.teacherid=t1.tid where s1.teacherid is null; +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ 1 row in set (0.00 sec)
和交叉连接不一样 mysql不支持full outer join
Requête à trois tables
MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid -> union -> select * from s1 right outer join t1 on s1.teacherid=t1.tid; +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang | 45 | M | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ 26 rows in set (0.00 sec)
MariaDB [hellodb]> select * from (select s.stuid,s.name s_name,s.teacherid,t.tid,t.name t_name from s1 s left outer join t1 t on s.teacherid=t.tid union select s.stuid,s.name,s.teacherid,t.tid,t.name from s1 s right outer join t1 t on s.teacherid=t.tid) as a where a.teacherid is null or a.tid is null; +-------+---------------+-----------+------+---------------+ | stuid | s_name | teacherid | tid | t_name | +-------+---------------+-----------+------+---------------+ | 2 | Shi Potian | 7 | NULL | NULL | | 3 | Xie Yanke | 16 | NULL | NULL | | 6 | Shi Qing | NULL | NULL | NULL | | 7 | Xi Ren | NULL | NULL | NULL | | 8 | Lin Daiyu | NULL | NULL | NULL | | 9 | Ren Yingying | NULL | NULL | NULL | | 10 | Yue Lingshan | NULL | NULL | NULL | | 11 | Yuan Chengzhi | NULL | NULL | NULL | | 12 | Wen Qingqing | NULL | NULL | NULL | | 13 | Tian Boguang | NULL | NULL | NULL | | 14 | Lu Wushuang | NULL | NULL | NULL | | 15 | Duan Yu | NULL | NULL | NULL | | 16 | Xu Zhu | NULL | NULL | NULL | | 17 | Lin Chong | NULL | NULL | NULL | | 18 | Hua Rong | NULL | NULL | NULL | | 19 | Xue Baochai | NULL | NULL | NULL | | 20 | Diao Chan | NULL | NULL | NULL | | 21 | Huang Yueying | NULL | NULL | NULL | | 22 | Xiao Qiao | NULL | NULL | NULL | | 23 | Ma Chao | NULL | NULL | NULL | | 24 | Xu Xian | NULL | NULL | NULL | | NULL | NULL | NULL | 2 | Zhang Sanfeng | +-------+---------------+-----------+------+---------------+ 22 rows in set (0.00 sec)
取学生姓名，成绩，科目。
自联结顾名思义就是把一张表假设为两张一样的表，然后在做“多表查询”
先构建一张表
MariaDB [hellodb]> create table emp (id int, name char(20),leaderid int); Query OK, 0 rows affected (0.01 sec) MariaDB [hellodb]> insert emp value(1,'huangshang',null); Query OK, 1 row affected (0.00 sec) MariaDB [hellodb]> insert emp value(2,'taihou','huangshang'); ERROR 1366 (22007): Incorrect integer value: 'huangshang' for column `hellodb`.`emp`.`leaderid` at row 1 MariaDB [hellodb]> insert emp value(2,'taihou',1); Query OK, 1 row affected (0.00 sec) MariaDB [hellodb]> insert emp value(3,'guifei',2); Query OK, 1 row affected (0.00 sec) MariaDB [hellodb]> insert emp value(4,'shufei',3); Query OK, 1 row affected (0.00 sec) MariaDB [hellodb]> select * from emp; +------+------------+----------+ | id | name | leaderid | +------+------------+----------+ | 1 | huangshang | NULL | | 2 | taihou | 1 | | 3 | guifei | 2 | | 4 | shufei | 3 | +------+------------+----------+ 4 rows in set (0.00 sec)
查询表里的上级的姓名。
MariaDB [hellodb]> select * from emp as e inner join emp as l on e.leaderid=l.id; +------+--------+----------+------+------------+----------+ | id | name | leaderid | id | name | leaderid | +------+--------+----------+------+------------+----------+ | 2 | taihou | 1 | 1 | huangshang | NULL | | 3 | guifei | 2 | 2 | taihou | 1 | | 4 | shufei | 3 | 3 | guifei | 2 | +------+--------+----------+------+------------+----------+ 3 rows in set (0.00 sec)
MariaDB [hellodb]> select e.name emp,l.name leader from emp as e inner join emp as l on e.leaderid=l.id; +--------+------------+ | emp | leader | +--------+------------+ | taihou | huangshang | | guifei | taihou | | shufei | guifei | +--------+------------+ 3 rows in set (0.00 sec)
MariaDB [hellodb]> select e.name emp,l.name leader from emp as e left join emp as l on e.leaderid=l.id; +------------+------------+ | emp | leader | +------------+------------+ | taihou | huangshang | | guifei | taihou | | shufei | guifei | | huangshang | NULL | +------------+------------+ 4 rows in set (0.00 sec)
SQL语句的关键字执行顺序
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