#Mysql Join
- 内连接就是计算结果集的交集
SELECT * FROM table_a, table_b WHERE table_a.id = table_b.id##左右外部连接（内连） - 左外部连接是计算左表全部数据以及和右表有交集的数据
SELECT * FROM table_a LEFT OUTER JOIN table_b ON table_a.id = table_b.id - 右外部连接是计算右表全部数据以及和左表有交集的数据
SELECT * FROM table_a RIGHT OUTER JOIN table_b ON table_a.id = table_b.id##左右外部连接不内连 - 只计算左表排除和右表交集后的数据（右表结果集为null的数据剔除）
SELECT * FROM table_a LEFT OUTER JOIN table_b ON table_a.id = table_b.id WHERE table_b.id IS null - 只计算右表排除和左表交集后的数据（左表结果集为null的数据剔除）
SELECT * FROM table_a RIGHT OUTER JOIN table_b ON table_a.id = table_b.id WHERE table_a.id IS null##全外连接 - 计算左右表结果集的交集以外的数据
SELECT * FROM table_a LEFT OUTER JOIN table_b ON table_a.id = table_b.id WHERE table_b.id IS null UNION SELECT * FROM table_a RIGHT OUTER JOIN table_b ON table_a.id = table_b.id WHERE table_a.id IS null##全外内连接 - 计算结果集的并集
SELECT * FROM table_a LEFT OUTER JOIN table_b ON table_a.id = table_b.id UNION SELECT * FROM table_a RIGHT OUTER JOIN table_b ON table_a.id = table_b.id