下圖展示了 LEFT JOIN、RIGHT JOIN、INNER JOIN、OUTER JOIN 相關的 7 種用法。
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
如果B有條重複記錄,A就會增加多條,因此要用如下方法解決:
SELECT <select_list>
FROM Table_A A
LEFT JOIN (SELECT <select_list/(sum(X),max(X))> FROM Table_B GROUP B.key) 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
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
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
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