php检查数据库中是否存在数字

Question

basically i dont want duplicate number in certain field. how do i do that?

table user:
id   name    group
1    a        2
2    b        3
3    c        1
4    d        6
5    e        5

$q = $db->query("SELECT COUNT(t_group) FROM user");
$r = $q->fetch_row;
if($r[0] > 0) :
     $rand_no = rand(1,10);
     $db->query("INSERT INTO user(name, group) VALUES('$name','$rand_no')");
endif;

Answer 1

Use insert ... where not exists

Example code

//prevent those pesky SQL injection attacks
$rand_no = mysql_real_escape_string($rand_no);
$name = mysql_real_escape_string($name);

//Only insert if group is not already used
$db->query("insert into user(name, `group`) 
            VALUES('$name',$rand_no) 
            where not exists 
              (select `group` from user where `group` = '$rand_no') )";

I've added the first two lines to remind you no to forget to escape those values to prevent SQL-injection attacks. (if $rand_no is generated by the php code, there's no need to escape it of course, but if a user can manipulate it then you should)

Secondly group is a reserved word, if you want to use it in a query you need to bracket it in backquotes ' ` '.

EDIT:
Enforce it in the database
Set the field group to be a unique field using ALTER TABLE

ALTER TABLE CHANGE COLUMN `group` `group` UNIQUE