【JOIN】关键字在MySql中的详细使用

[INNER JOIN（内连接）](#INNER JOIN（内连接）)

[LEFT JOIN（左连接）](#LEFT JOIN（左连接）)

[RIGHT JOIN（右连接）](#RIGHT JOIN（右连接）)

[FULL JOIN（全连接）](#FULL JOIN（全连接）)

示例图形化解释JOIN的不同类型

[INNER JOIN：](#INNER JOIN：)

[LEFT JOIN：](#LEFT JOIN：)

[RIGHT JOIN：](#RIGHT JOIN：)

[FULL JOIN：](#FULL JOIN：)

INNER JOIN（内连接）

返回两个表中匹配的行。

表达方式1：

复制代码

SELECT * 
FROM table1 
INNER JOIN table2 
ON table1.column = table2.column;

表达方式2：

复制代码

SELECT * 
FROM table1, table2 
WHERE table1.column = table2.column;

LEFT JOIN（左连接）

返回左表中的所有行以及与右表匹配的行。

表达方式1：

复制代码

SELECT * 
FROM table1 
LEFT JOIN table2 
ON table1.column = table2.column;

表达方式2：

复制代码

SELECT * 
FROM table1 
LEFT OUTER JOIN table2 
ON table1.column = table2.column;

RIGHT JOIN（右连接）

返回右表中的所有行以及与左表匹配的行。

表达方式1：

复制代码

SELECT * 
FROM table1 
RIGHT JOIN table2 
ON table1.column = table2.column;

表达方式2：

复制代码

SELECT * 
FROM table1 
RIGHT OUTER JOIN table2 
ON table1.column = table2.column;

FULL JOIN（全连接）

返回左右表中的所有行。

复制代码

SELECT * 
FROM table1 
FULL JOIN table2 
ON table1.column = table2.column;

示例图形化解释JOIN的不同类型

INNER JOIN

复制代码

+----+-------+-----+-------+
| ID | Name  | Age | Grade |
+----+-------+-----+-------+
| 1  | John  | 24  | A     |
| 2  | Alice | 22  | B     |
| 3  | Bob   | 25  | A     |
+----+-------+-----+-------+

+--------+--------+
| ID     | City   |
+--------+--------+
| 1      | London |
| 2      | Paris  |
| 4      | Berlin |
+--------+--------+

After INNER JOIN:

+----+-------+-----+-------+--------+--------+
| ID | Name  | Age | Grade | ID     | City   |
+----+-------+-----+-------+--------+--------+
| 1  | John  | 24  | A     | 1      | London |
| 2  | Alice | 22  | B     | 2      | Paris  |
+----+-------+-----+-------+--------+--------+

LEFT JOIN

复制代码

+----+-------+-----+-------+
| ID | Name  | Age | Grade |
+----+-------+-----+-------+
| 1  | John  | 24  | A     |
| 2  | Alice | 22  | B     |
| 3  | Bob   | 25  | A     |
+----+-------+-----+-------+

+--------+--------+
| ID     | City   |
+--------+--------+
| 1      | London |
| 2      | Paris  |
| 4      | Berlin |
+--------+--------+

After LEFT JOIN:

+----+-------+-----+-------+--------+--------+
| ID | Name  | Age | Grade | ID     | City   |
+----+-------+-----+-------+--------+--------+
| 1  | John  | 24  | A     | 1      | London |
| 2  | Alice | 22  | B     | 2      | Paris  |
| 3  | Bob   | 25  | A     | NULL   | NULL   |
+----+-------+-----+-------+--------+--------+

RIGHT JOIN

复制代码

+----+-------+-----+-------+
| ID | Name  | Age | Grade |
+----+-------+-----+-------+
| 1  | John  | 24  | A     |
| 2  | Alice | 22  | B     |
| 3  | Bob   | 25  | A     |
+----+-------+-----+-------+

+--------+--------+
| ID     | City   |
+--------+--------+
| 1      | London |
| 2      | Paris  |
| 4      | Berlin |
+--------+--------+

After RIGHT JOIN:

+----+-------+-----+-------+--------+--------+
| ID | Name  | Age | Grade | ID     | City   |
+----+-------+-----+-------+--------+--------+
| 1  | John  | 24  | A     | 1      | London |
| 2  | Alice | 22  | B     | 2      | Paris  |
| NULL | NULL  | NULL   | NULL    | 4      | Berlin |
+----+-------+-----+-------+--------+--------+

FULL JOIN

复制代码

+----+-------+-----+-------+
| ID | Name  | Age | Grade |
+----+-------+-----+-------+
| 1  | John  | 24  | A     |
| 2  | Alice | 22  | B     |
| 3  | Bob   | 25  | A     |
+----+-------+-----+-------+

+--------+--------+
| ID     | City   |
+--------+--------+
| 1      | London |
| 2      | Paris  |
| 4      | Berlin |
+--------+--------+

After FULL JOIN:

+----+-------+-----+-------+--------+--------+
| ID | Name  | Age | Grade | ID     | City   |
+----+-------+-----+-------+--------+--------+
| 1  | John  | 24  | A     | 1      | London |
| 2  | Alice | 22  | B     | 2      | Paris  |
| 3  | Bob   | 25  | A     | NULL   | NULL   |
| NULL | NULL  | NULL   | NULL    | 4      | Berlin |
+----+-------+-----+-------+--------+--------+