ref:https://www.cnblogs.com/bluealine/p/7832219.htmlphp
1)查看表结构:desc table_name;html
2)查看建立表的sql语句:show create table mytable;mysql
3)select count(username) from user;//count(username)能够换成count(*),count(0)web
4)union和union all的区别是,union会自动压缩多个结果集合中的重复结果,而union all则将全部的结果所有显示出来,不论是不是重复。sql
字段名 | 数字类型 | 数据宽度 | 是否为空 | 是否主键 | 自动增长 | 默认值 |
id | int | 4 | 否 | primary key | auto_increment | |
name | char | 20 | 否 | |||
sex | int | 4 | 否 | 0 | ||
degree | double | 16 | 是 |
FirstName | LastName | Age |
---|---|---|
Peter | Griffin | 35 |
Glenn | Quagmire | 33 |
<?php $con = mysql_connect("localhost","peter","abc123"); if (!$con) { die('Could not connect: ' . mysql_error()); } mysql_select_db("my_db", $con); mysql_query("DELETE FROM Persons WHERE LastName='Griffin'"); mysql_close($con); ?>在此次删除以后,表是这样的:
FirstName | LastName | Age |
---|---|---|
Glenn | Quagmire | 33 |