摘要:
1.等值连接(内连接) 2.自连接 3.自然连接 4.外连接(省略左外连接和右外连接) 5.合并查询数据记录 UNION 会去掉重复项 UNION ALL 不会去掉重复项 6.子查询(效率远高于连接查询) 带关键字的子查询 阅读全文
always chase after what I like, but never forget what I dream of."
always chase after what I like, but never forget what I dream of."