MySql中JOIN关键字详细使用
作者：b***910
文章介绍了SQL中的四种连接类型：INNERJOIN、LEFTJOIN、RIGHTJOIN和FULLJOIN,并通过图形化示例展示了它们的区别,本文结合实例代码给大家介绍的非常详细,感兴趣的朋友跟随小编一起看看吧
INNER JOIN（内连接）
返回两个表中匹配的行。
表达方式1：
SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column;
表达方式2：
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：
SELECT * FROM table1 LEFT JOIN table2 ON table1.column = table2.column;
表达方式2：
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：
SELECT * FROM table1 RIGHT JOIN table2 ON table1.column = table2.column;
表达方式2：
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。
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
+----+-------+-----+-------+ | 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
+----+-------+-----+-------+ | 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
+----+-------+-----+-------+ | 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
+----+-------+-----+-------+ | 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 | +----+-------+-----+-------+--------+--------+
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