MySQL中的内部连接
这是我的两张桌子: 表名:朋友MySQL中的内部连接,mysql,sql,Mysql,Sql,这是我的两张桌子: 表名:朋友 +-------+---------+---------+-------------------+ | id | firstName | lastName | city | +-------+--------------+------------+-----------+ | 1 | dudi | edri | london | | 2 | maor | azulay
+-------+---------+---------+-------------------+
| id | firstName | lastName | city |
+-------+--------------+------------+-----------+
| 1 | dudi | edri | london |
| 2 | maor | azulay | madrid |
| 3 | batel | azulay | tel aviv |
| 4 | nir | cohen | barcelona |
| 5 | evia | perez | miami |
| 6 | neria | perez | new-york |
| 7 | nevo | kakoun | roma |
+-------+---------+---------+-------------------+
+-------+---------+---------+-----------------+
| id | firstName | amount | status |
+-------+--------------+----------+-----------+
| 1 | dudi | 5684 | shipped |
| 2 | maor | 4896 | shipped |
| 3 | batel | 2496 | delay |
+-------+--------------+----------+-----------+
+-------+---------+---------+-----------------+
| id | friendID | amount | status |
+-------+--------------+----------+-----------+
| 1 | 1 | 5684 | shipped |
| 2 | 2 | 4896 | shipped |
| 3 | 3 | 2496 | delay |
+-------+--------------+----------+-----------+
表名:订单
+-------+---------+---------+-------------------+
| id | firstName | lastName | city |
+-------+--------------+------------+-----------+
| 1 | dudi | edri | london |
| 2 | maor | azulay | madrid |
| 3 | batel | azulay | tel aviv |
| 4 | nir | cohen | barcelona |
| 5 | evia | perez | miami |
| 6 | neria | perez | new-york |
| 7 | nevo | kakoun | roma |
+-------+---------+---------+-------------------+
+-------+---------+---------+-----------------+
| id | firstName | amount | status |
+-------+--------------+----------+-----------+
| 1 | dudi | 5684 | shipped |
| 2 | maor | 4896 | shipped |
| 3 | batel | 2496 | delay |
+-------+--------------+----------+-----------+
+-------+---------+---------+-----------------+
| id | friendID | amount | status |
+-------+--------------+----------+-----------+
| 1 | 1 | 5684 | shipped |
| 2 | 2 | 4896 | shipped |
| 3 | 3 | 2496 | delay |
+-------+--------------+----------+-----------+
我的问题是:
我想要没有秩序的朋友。
答案是:
| 4 | nir | cohen | barcelona |
| 5 | evia | perez | miami |
| 6 | neria | perez | new-york |
| 7 | nevo | kakoun | roma |
+-------+---------+---------+-------------------+
我是如何使用内部联接编写查询的。
谢谢。您不应该在
订单
中使用名字
作为外键。外键应引用主键。使用ID
fromFRIENDS
如:
表名:订单
+-------+---------+---------+-------------------+
| id | firstName | lastName | city |
+-------+--------------+------------+-----------+
| 1 | dudi | edri | london |
| 2 | maor | azulay | madrid |
| 3 | batel | azulay | tel aviv |
| 4 | nir | cohen | barcelona |
| 5 | evia | perez | miami |
| 6 | neria | perez | new-york |
| 7 | nevo | kakoun | roma |
+-------+---------+---------+-------------------+
+-------+---------+---------+-----------------+
| id | firstName | amount | status |
+-------+--------------+----------+-----------+
| 1 | dudi | 5684 | shipped |
| 2 | maor | 4896 | shipped |
| 3 | batel | 2496 | delay |
+-------+--------------+----------+-----------+
+-------+---------+---------+-----------------+
| id | friendID | amount | status |
+-------+--------------+----------+-----------+
| 1 | 1 | 5684 | shipped |
| 2 | 2 | 4896 | shipped |
| 3 | 3 | 2496 | delay |
+-------+--------------+----------+-----------+
并使用左外部联接进行查询
:
SELECT f.*
FROM FRIENDS f
LEFT JOIN ORDERS o
ON f.ID = o.friendID
WHERE o.ID IS NULL;
另一种可能是使用相关子查询
:
SELECT f.*
FROM FRIENDS f
WHERE NOT EXISTS (SELECT 1
FROM orders o
WHERE o.friendID = f.ID);
表:
CREATE TABLE friends(
id INTEGER NOT NULL PRIMARY KEY -- you can add AUTO_INCREMENT if needed
...
);
CREATE TABLE orders(
id INTEGER NOT NULL PRIMARY KEY
,friendID INTEGER NOT NULL
,FOREIGN KEY (friendID) REFERENCES friends(id)
...
);
您不应该在
ORDERS
中使用firstName
作为外键。外键应引用主键。使用ID
fromFRIENDS
如:
表名:订单
+-------+---------+---------+-------------------+
| id | firstName | lastName | city |
+-------+--------------+------------+-----------+
| 1 | dudi | edri | london |
| 2 | maor | azulay | madrid |
| 3 | batel | azulay | tel aviv |
| 4 | nir | cohen | barcelona |
| 5 | evia | perez | miami |
| 6 | neria | perez | new-york |
| 7 | nevo | kakoun | roma |
+-------+---------+---------+-------------------+
+-------+---------+---------+-----------------+
| id | firstName | amount | status |
+-------+--------------+----------+-----------+
| 1 | dudi | 5684 | shipped |
| 2 | maor | 4896 | shipped |
| 3 | batel | 2496 | delay |
+-------+--------------+----------+-----------+
+-------+---------+---------+-----------------+
| id | friendID | amount | status |
+-------+--------------+----------+-----------+
| 1 | 1 | 5684 | shipped |
| 2 | 2 | 4896 | shipped |
| 3 | 3 | 2496 | delay |
+-------+--------------+----------+-----------+
并使用左外部联接进行查询
:
SELECT f.*
FROM FRIENDS f
LEFT JOIN ORDERS o
ON f.ID = o.friendID
WHERE o.ID IS NULL;
另一种可能是使用相关子查询
:
SELECT f.*
FROM FRIENDS f
WHERE NOT EXISTS (SELECT 1
FROM orders o
WHERE o.friendID = f.ID);
表:
CREATE TABLE friends(
id INTEGER NOT NULL PRIMARY KEY -- you can add AUTO_INCREMENT if needed
...
);
CREATE TABLE orders(
id INTEGER NOT NULL PRIMARY KEY
,friendID INTEGER NOT NULL
,FOREIGN KEY (friendID) REFERENCES friends(id)
...
);
您不应该在
订单中使用firstName作为外键。它没有任何意义-外键应该引用主键。要进行内部联接的列是:idCorrect。所以要解决这个问题。你不应该在ORDERS
中使用firstName作为外键。它没有任何意义-外键应该引用主键。要进行内部联接的列是:idCorrect。所以要解决这个问题。