### has
确定数据是否存在
has($table, $where)
* ##### table [string]
表名.
* ##### where [array]
WHERE 条件.
has($table, $join, $where)
* ##### table [string]
表名.
* ##### join [array]
多表查询.
* ##### where [array]
WHERE条件.
Return: [boolean] 返回 TRUE 或者 FALSE.
可用于做密码判断。
~~~
if ($database->has("account", [
"AND" => [
"OR" => [
"user_name" => "foo",
"email" => "foo"
],
"password" => "12345"
]
]))
{
echo "Password is correct.";
}
else
{
echo "Password error.";
}
~~~
