CODEWITHSUNDEEP
phpsql
supermitch
supermitch

Reputation: 2952

How to check whether SELECT EXISTS returns a value or not?

I am trying to quickly determine if a user_ID is the owner of a 'goal'. I believe my SQL query is good, but I'm trying to find a nice way of checking the result!

In this case, no matter what I put for $obj_id or $user_id, my function returns true. I assume it's because mysql_num_rows is counting even a false result as a row? So what PHP code should I use to check to see if the result exists or not?

Note that I want something short and elegant! I know I could do it the long way (check count(*), return mysql_assoc then check the count value...) but that is long winded and ugly.

Any ideas? Thanks!

$query = "SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')";
if (@mysql_num_rows(mysql_query($query))!=1) {
    return false;
} else {
    return true;
}

Upvotes: 25

Views: 59968

Answers (8)

Sergey Shramuk
Sergey Shramuk

Reputation: 11

Really working config for MySQL:

$sql="SELECT EXISTS (Select * FROM $dbname.$dbrel WHERE Index_r=$idx AND ... LIMIT 
1)";    
$r1=mysqli_fetch_row(mysqli_query($conn, $sql));
if (current($r1) == 0) {when no recoeds} else {when exist records }

Upvotes: 1

Siebe Jongebloed
Siebe Jongebloed

Reputation: 4844

SELECT EXISTS always returns a row! The following code uses the fastest MySql query(according to this answer: https://stackoverflow.com/a/10688065/3710053) and gives in PHP the correct result:

$link = mysqli_connect($DB_SERV, $DB_USER, $DB_PASS, $DB_NAME);
$query = "SELECT EXISTS (SELECT * FROM goals 
                      WHERE goal_ID='$obj_id' 
                        AND user_ID='$user_id' 
                      LIMIT 1) 
      as `row_exists`";

if(mysqli_fetch_assoc(mysqli_query($link,$query))['row_exists'] ===0) {
   // Nothing found!
}

Upvotes: 1

levent
levent

Reputation: 9

mysql_result(mysql_query("SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')"),0);

Upvotes: 0

Esteban
Esteban

Reputation: 884

Counting how many rows match the criteria should be easier:

$sql = SELECT COUNT(*) FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id'
$query = mysql_query($sql);
$result = mysql_fetch_row($query);

return $result[0] >= 1;

Upvotes: 2

Bas
Bas

Reputation: 25

This way is probably faster.

$query = "SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')";

if(mysql_num_rows(mysqli_query($query)) < 1) {
   // Nothing found!
}

Upvotes: 2

gbn
gbn

Reputation: 432220

Don't bother with EXISTS. The in-line exists will always give one row containing "true" or "false".

You're looking for either "zero rows" or "at least one row" so change the query to something like this and then check how many rows are returned

SELECT 1 FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id' LIMIT 1

Upvotes: 42

tareco
tareco

Reputation: 1191

what about this: 

$query = "SELECT EXISTS (SELECT * FROM goals WHERE goal_ID='$obj_id' AND user_ID='$user_id')";

return  mysql_query($query) ? false : true;

Upvotes: 0

Brad Mace
Brad Mace

Reputation: 27886

I like gbn's answer the best, but I wanted to point out that this:

if (@mysql_num_rows(mysql_query($query))!=1) {
     return false;
} else {
     return true;
}

can be simplified to:

return @mysql_num_rows(mysql_query($query)) == 1;

Upvotes: 10

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