php怎么判断数据库数据是否存在

$data = array()

$db_name_php = 'books'

if (!mysql_connect('localhost', 'root', '123456')) {

echo '不能连接到mysql'

exit

}

$result = mysql_query('show databases')

While($row = mysql_fetch_assoc($result)){

$data[] = $row['Database']

}

unset($result, $row)

mysql_close()

print_r($data)

echo '<br><br>' if (in_array(strtolower($db_name_php), $data))

echo '[',$db_name_php,']数据库存在'

else

echo '[',$db_name_php,']数据库不存在'

?>

$con = mysql_connect("localhost", "hello", "321")

if (!$con)

{

die('Could not connect: ' . mysql_error())

}

$db_selected = mysql_select_db("test_db", $con)

if (!$db_selected)

{

die ("Can\'t use test_db : " . mysql_error())

}

mysql_close($con)

?>

其实就是先登录再选择数据库

mysql_select_db