1.INNER JOIN
语法:SELECT column_name(s) FROM table1 JOIN table2
ON table1.column_name=table2.column_name
eg1: SELECT w.name,w.url,a.count,a.data
FROM websites as w JOIN access_log as a
ON w.id=a.site_id ORDER BY a.count;
注:INNER JOIN 关键字在表中存在至少一个匹配时返回行。如果 "Websites" 表中的行在 "access_log" 中没有匹配,则不会列出这些行。
2.LEFT JOIN
语法:SELECT column_name(s) FROM table1 LEFT JOIN table2
ON table1.column_name=table2.column_name
注:查询结果 右表种没有的匹配记录也会显示
3.RIGHT JOIN
注:RIGHT JOIN 关键字从右表返回所有的行,即使左表中没有匹配
4.FULL JOIN