检查值是否存在于MySQL行中

Question

I have a php variable: $foo

My MySQL table called data has the following structure:

id    var    header

1     zj3     http://google.com

I would like to check if $foo is all ready in var row.

If it is I would like to echo header ("http://google.com")

How would you approach this?

Thanks in advance, please ask if any clarification is needed!

Answer 1

Your query should be:

SELECT `header` FROM `data` WHERE `var` = '$foo'

This will return all the headers with a var value of $foo .

$db = mysqli_connect('localhost', 'username', 'password', 'database');
if($query = mysqli_query($db, "SELECT `header` FROM `data` WHERE `var` = '$foo'")){
  while($row = mysqli_fetch_assoc($query)){
    echo $row['header'];
  }
  mysqli_free_result($query);
}

Answer 2

first connect to the db

$query = mysql_query("SELECT var, header FROM data WHERE id='1'") or die(mysql_error());
while($row = mysql_fetch_assoc($query)){
    if($foo == $row['var']){
        echo $row['header'];
    }
}

EDIT: changed equality statement based on your edit

Answer 3

are you asking if $foo matches any of the fields in data , or if $foo=some_field ? Here for if you want $foo==var .

$foo='somevalue';
$query="SELECT id, var, header FROM `data` WHERE var='$foo'";
$result=mysqli_query($query);
if($result->num_rows==0) 
  $loc= 'http://google.com';//default value for when there is no row that matches $foo
}else{
  $row=$result->fetch_assoc(); //more than one row is useless since the first header('Location: x') command sends the browser to a new page and away from your script.
  $loc=$row['header'];

}
header ("Location: $loc);
exit;

ETA: since you've edited your question, it appears that you want to echo the header column if your search value matches your var column. The above won't work for that.

Answer 4

It's not difficult at all, If I understand correctly then this should help you.

// Query Variable / Contains you database query information
$results = $query;

// Loop through like so if the results are returned as an array
foreach($results as $result)
{
    if(!$result['var'])
        echo $result['header'];
}

// Loop through like so if the results are returned as an object
foreach($results as $result)
{
    if(!$result->var)
        echo $result->header;
}

Answer 5

Here's a template for all the "does it exist" questions.

This is the only thing that actually worked for me so far and is not deprecated.

if ($query = mysqli_query($link, "SELECT header FROM data WHERE var = '$foo'")) {

        $header = mysqli_fetch_assoc($query);

        if ($header) {

            // The variable with value $foo exists.
        }
        else {

            // The variable with value $foo doesn't exist.
        }
    }
    else {

        // The query didn't execute for some reason. (Dammit Obama!)
    }

WARNING!

Even if the variable DOES NOT EXIST the comparison between $query and mysqli_query() will always return TRUE .

The only way --which happened to me-- for the comparison to return FALSE is because of a syntax error in your query.

I don't know why it worked for the guy who wrote the accepted answer, maybe it's an update or maybe he had a syntax error and was so confident that he didn't check if it could ever be TRUE .

Here's the comment someone made for correcting his syntax:

"Add another ) before the { in the first line"

So, the accepted answer is WRONG!

Answer 6

You just want to know if $var's value is anywhere in that column (any row(s))?

SELECT COUNT(id) FROM data WHERE var = ?;

The result will be the number of rows for which the field var contains the value of $var.