How to get the result of a select count(*) query in PHP?

I have this query to use in PHP:

mysql_query("select count(*) from registeredUsers where email=".$_SESSION["username"]);

When I use echo to print out the开发者_如何学运维 result, nothing gets printed. What exactly is the return value from the above statement?

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Your code doesn't include any fetch statement. And as another answer notes, you need single quotes around $_SESSION["username"].

$result = mysql_query("select count(*) from registeredUsers where email='{$_SESSION['username']}'");

// Verify it worked
if (!$result) echo mysql_error();

$row = mysql_fetch_row($result);

// Should show you an integer result.
print_r($row);

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mysql_query returns a result resource. You can read the result with mysql_result

$res = mysql_query("select count(*) from registeredUsers where email='".mysql_real_escape_string($_SESSION["username"])."'");
echo mysql_result($res,0);

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You need single quotes around the session variable in your query

$result = mysql_query("SELECT COUNT(*) 
                       FROM registeredUsers 
                       WHERE email = '".$_SESSION['username']."' ");

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The count query will always return a value, which is 0 if no records are returned, or an integer above 0 if records match it.

It should at least be printing out 0, the query you posted means:

Get the number of records where the email address is equal to the session username

This might not make sense, do you mean to do where username = ".$_SESSION["username"] or something similar?

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You may want to echo out the query itself to determine that it is returning what you expect.

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mysql_query() returns a resource used to get information from the result set. Use a function such as mysql_fetch_array() to retrieve rows from the result set. In this case, there will only be one row.

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It should give you the amount of registere users who have the email address that you provide as the parameter to this query. (Might be a check if the given email address is already registered for another user.) If the email address is not yet registered, an empty field will be returned. (That might be the reason why nothing gets printed out in your case. Try it with an email address that you are certain of to be in the database.)

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$resultemp = mysql_query("select count(*) AS count from registeredUsers where email='{$_SESSION['username']}'");

// Verify mySQL Query Rresult

if (!$resultemp) echo mysql_error();

// Convert mySQL Result for PHP

$counter=mysql_fetch_assoc($resultemp);
$counter=$counter['count'];

// Print Total Employees

echo $counter;

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You need to use mysql_fetch_array() to return value in a user defined variable. Then have to print the returned value.

 $result=mysql_query("select count(*) from registeredUsers where email='{$_SESSION['username']}'")
 $COUNT_NUMBER=mysql_fetch_array($result); 
 echo "<br>1.Count=" .$COUNT_NUMBER[0]; 

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Try casting it to string before echoing it. As an int, 0 will display as an empty string.