左外连接

SELECT <select_list> 
FROM TableA A
LEFT JOIN TableB B
ON A.Key = B.Key

SELECT <select_list>
FROM TableA A
LEFT JOIN TableB B
ON A.Key = B.Key
WHERE B.Key IS NULL

右外连接

SELECT <select_list> 
FROM TableA A
RIGHT JOIN TableB B
ON A.Key = B.Key

SELECT <select_list> 
FROM TableA A
RIGHT JOIN TableB B
ON A.Key = B.Key
WHERE A.Key IS NULL

全外连接

mysql不支持，需要用union

SELECT <select_list> 
FROM TableA A
FULL OUTER JOIN TableB B
ON A.Key = B.Key

SELECT <select_list> 
FROM TableA A
FULL OUTER JOIN TableB B
ON A.Key = B.Key
WHERE A.Key IS NULL
OR B.Key IS NULL

Mysql七种 JOIN 连接

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