我有两个表:
T1
A
B
C
D
T2
A
B
E
F
G
现在我要查询将合并这两个表但排除的查询
相同的记录。输出表应类似于:
T1T2
C
D
E
F
G
怎么做?
最佳答案
看起来您需要FULL OUTER JOIN
并排除公共部分。您可以使用以下方法进行模拟:
SELECT T1.col_name
FROM T1
LEFT JOIN T2
ON T1.col_name = T2.col_name
WHERE T2.col_name IS NULL
UNION
SELECT T2.col_name
FROM T2
LEFT JOIN T1
ON T1.col_name = T2.col_name
WHERE T1.col_name IS NULL;
SqlFiddleDemo
╔══════════╗
║ col_name ║
╠══════════╣
║ C ║
║ D ║
║ E ║
║ F ║
║ G ║
╚══════════╝
更多信息:Visual Representation of SQL Joins
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
不幸的是,
MySQL
不支持FULL OUTER JOIN
,所以我使用了2个LEFT JOIN
的并集。http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins中的所有图像
附录
但是,如果我有两个具有不同列的不同表,但是它们都有一个相同的列,该怎么办?所用的SELECT语句的列数不同
您可以使用其他列轻松扩展它。
SELECT 'T1' AS tab_name, T1.col_name, T1.col1, NULL AS col2
FROM T1
LEFT JOIN T2
ON T1.col_name= T2.col_name
WHERE T2.col_name IS NULL
UNION
SELECT 'T2' AS tab_name, T2.col_name, NULL, T2.col2
FROM T2
LEFT JOIN T1
ON T1.col_name= T2.col_name
WHERE T1.col_name IS NULL;
LiveDemo
输出:
╔══════════╦══════════╦══════╦═════════════════════╗
║ tab_name ║ col_name ║ col1 ║ col2 ║
╠══════════╬══════════╬══════╬═════════════════════╣
║ T1 ║ C ║ 3 ║ ║
║ T1 ║ D ║ 4 ║ ║
║ T2 ║ E ║ ║ 2016-01-03 00:00:00 ║
║ T2 ║ F ║ ║ 2016-01-02 00:00:00 ║
║ T2 ║ G ║ ║ 2016-01-01 00:00:00 ║
╚══════════╩══════════╩══════╩═════════════════════╝
关于mysql - 合并两个表,排除相同的记录,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/34610639/