INNER JOIN (内连接)
内连接:根据连接条件讲两张表的数据连接起来,如果没有符合的数据都会被过滤掉,留下符合条件的数据. -->INNER可以省略
SELECT <select_list>
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.Key;
LEFT JOIN(左连接)
左连接:显示两表中的所有列,展示左表的所有数据,若右表可以连接上则显示数据,关联不上显示为空
SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key;
RIGHT JOIN（右连接）
右连接:显示两表中的所有列,展示右表的所有数据,若左表可以连接上则显示数据,关联不上显示为空
SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key;
FULL JOIN(外连接)
外连接:显示两表所有的列,展示两表的所有数据,根据连接条件进行等值连接,找不到时,会在乡音位置显示为空.
SELECT <select_list>
FROM Table_A A
FULL JOIN Table_B B
ON A.Key = B.Key;
CROSS JOIN(交叉连接或笛卡尔积连接)
交叉连接:笛卡尔积原则,结果为第一张表的数据乘以第二张表的数据
SELECT <select_list>
FROM Table_A
CROSS JOIN Table_B ;
或
SELECT <select_list>
FROM Table_A,Table_B ;
LEFT JOIN EXCLUDING INNER JOIN（左连接-内连接）
SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL;
RIGHT JOIN EXCLUDING INNER JOIN（右连接-内连接）
SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL;
OUTER JOIN EXCLUDING INNER JOIN（外连接-内连接)
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;
