本文通过图形方式清晰地描述了SQL中各种连接关系，包括INNER JOIN、LEFT JOIN、RIGHT JOIN、OUTER JOIN及其排除内连接的变体。适合初学者及需要复习SQL连接概念的读者。
文章目录
LEFT JOIN EXCLUDING INNER JOIN
RIGHT JOIN EXCLUDING INNER JOIN
OUTER JOIN EXCLUDING INNER JOIN
写在前面
翻出来一篇笔记，忘了啥时候整理的，好像是在一个外国网站上看到的。
作者应该是个程序员，用图形方式清楚的描述出SQL之间的各种连接关系，非常的易懂。原文我已经找不到了，向原作者致敬！
INNER JOIN
SELECT
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.KeyLEFT JOIN
SELECT
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.KeyRIGHT JOIN
SELECT
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.KeyOUTER JOIN
SELECT
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.KeyLEFT JOIN EXCLUDING INNER JOIN
SELECT
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULLRIGHT JOIN EXCLUDING INNER JOIN
SELECT
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULLOUTER JOIN EXCLUDING INNER JOIN
SELECT
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL OR B.Key IS NULL总结
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