create table person(id int primary key auto_increment,name varchar(10),age int);
drop table user; create table user(username varchar(10),password varchar(10));
insert into user values('libai','admin'); insert into user values('liubei','admin');
select count(*) from user where username='liubei' and password='admin';
select count(*) from user
where username='asdfsdf' and password='' or '1'='1'
' or '1'='1
create table hero(id int primary key auto_increment,name varchar(10),money int); insert into hero values(null,'超人',50),(null,'蝙蝠侠',5000);
数据库元数据:数据库相关的部分信息
//得到数据库的元数据
DatabaseMetaData dbmd = conn.getMetaData();
System.out.println("数据库版本:"+
dbmd.getDriverVersion());
System.out.println("用户名:"+
dbmd.getUserName());
System.out.println("数据库地址:"+
dbmd.getURL());
System.out.println("数据库厂商:"+
dbmd.getDatabaseProductName());
表的元数据:表相关的部分信息
ResultSet rs =
stat.executeQuery("select * from emp");
//得到表相关的源数据
ResultSetMetaData rsmd = rs.getMetaData();
//得到表的字段数量
int count = rsmd.getColumnCount();
for (int i = 0; i < count; i++) {
System.out.println("字段名"
+rsmd.getColumnName(i+1));
System.out.println("字段类型"
+rsmd.getColumnTypeName(i+1));
}