我有两个表,X和Y：mysql> select * from X; +------+------+ | id | colX | +------+------+ | 2001 | 0 | | 2002 | 0 | | 2003 | 0 | | 2004 | 0 | | 2005 | 0 | | 2006 | 10 | | 2007 | 10 | +------+------+mysql> SELECT * FROM Y; +------+------+-------+ | id | colY | score | +------+------+-------+ | 2001 | 10 | 3 | | 2004 | 0 | 12 | | 2005 | 0 | 15 | | 2007 | 0 | ...
一般所说的左连接，外连接是指左外连接，右外连接。做个简单的测试你看吧。 先说左外连接和右外连接： [TEST1@orcl#16-12月-11] SQL>select * from t1;ID NAME ---------- --------------------1 aaa2 bbb[TEST1@orcl#16-12月-11] SQL>select * from t2;ID AGE ---------- ----------1 203 30 左外连接： [TEST1@orcl#16-12月-11] SQL>select * from t1 left join t2 on t1.id=t2.id;ID NAME ...
JOIN的含义就如英文单词“join”一样，连接两张表，大致分为内连接，外连接，右连接，左连接，自然连接。这里描述先甩出一张用烂了的图，然后插入测试数据。 CREATE TABLE t_blog(id INT PRIMARY KEY AUTO_INCREMENT,title VARCHAR(50),typeId INT);SELECT * FROM t_blog;+----+-------+--------+| id | title | typeId |+----+-------+--------+| 1 | aaa | 1 || 2 | bbb | 2 || 3 | ccc | 3 || 4 | d...