概述
INNER JOIN (内连接)
markdown
Table A
| ID | Name |
| 1 | Alice |
| 2 | Bob |
Table B
| ID | Status |
| 1 | Active |
| 3 | Inactive |
INNER JOIN 结果
| ID | Name | Status |
| 1 | Alice | Active |
LEFT JOIN (左连接)
markdown
Table A
| ID | Name |
| 1 | Alice |
| 2 | Bob |
Table B
| ID | Status |
| 1 | Active |
| 3 | Inactive |
LEFT JOIN 结果
| ID | Name | Status |
| 1 | Alice | Active |
| 2 | Bob | NULL |
RIGHT JOIN (右连接)
markdown
Table A
| ID | Name |
| 1 | Alice |
| 2 | Bob |
Table B
| ID | Status |
| 1 | Active |
| 3 | Inactive |
RIGHT JOIN 结果
| ID | Name | Status |
| 1 | Alice | Active |
| 3 | NULL | Inactive |
FULL JOIN (全连接)
markdown
Table A
| ID | Name |
| 1 | Alice |
| 2 | Bob |
Table B
| ID | Status |
| 1 | Active |
| 3 | Inactive |
FULL JOIN 结果
| ID | Name | Status |
| 1 | Alice | Active |
| 2 | Bob | NULL |
| 3 | NULL | Inactive |
CROSS JOIN (交叉连接)
markdown
Table A
| ID | Name |
| 1 | Alice |
| 2 | Bob |
Table B
| ID | Status |
| 1 | Active |
| 2 | Inactive |
CROSS JOIN 结果
| ID_A | Name | ID_B | Status |
| 1 | Alice | 1 | Active |
| 1 | Alice | 2 | Inactive |
| 2 | Bob | 1 | Active |
| 2 | Bob | 2 | Inactive |
请注意，在CROSS JOIN的结果中，我添加了ID_A和ID_B来区分来自不同表的ID字段，以避免混淆。在实际应用中，如果两个表中的列名相同，通常需要在查询中重命名至少一个列，以便能够清晰地引用它们。
