UNION：七种连接介绍

https://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins

INNER JOIN

SELECT <select_list> 
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.Key

LEFT JOIN

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key

RIGHT JOIN

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key

OUTER JOIN

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key

Left Excluding JOIN 左排除连接

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

Right Excluding JOIN 右排除连接

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

Outer Excluding JOIN 外排除连接

SELECT <select_list>
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