在MySql SQL语句中插入PHP变量

I'm trying to do like this using PHP and MySql PDO:

//PHP Variables
$msg_a = 'Too Little';
$msg_b = 'Score OK';

$sql = "select if(stdScore >= stdRequired, $msg_a, $msg_b) from scores;"

$results = $conn->prepare($Sql);

$results->execute();

AFAIK this should have worked. But I keep getting the following error message:

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '

How can something like this be done?

$results = $conn->prepare($Sql);

---------------------------------------------^ (capital S)

it should be with a lowercase s

$results = $conn->prepare($sql);

because you have:

$sql = "select if(stdScore >= stdRequired, $msg_a, $msg_b) 
        from scores";(//semicolon after double quotes)

---^
with a lowercase s ($sql)

Have you tried it this way ?

$sql = "select if(stdScore >= stdRequired, "'.$msg_a.'", "'.$msg_b.'") from scores;"

Can you try this,

$sql = "select if(stdScore >= stdRequired, $msg_a, $msg_b) from scores";

$results = $conn->prepare($sql);

Since you're already using PDO don't do query string interpolation leaving your code vulnerable to sql injections and value escaping problems. Instead use prepared statements properly.

Your code could've looked something like

$msg_a = 'Too Little';
$msg_b = 'Score OK';
// use placeholders in a query string
$sql = "SELECT IF(stdScore >= stdRequired, :msg_a, :msg_b) msg FROM scores";
// prepare the statement
$query = $conn->prepare($sql);
// bind parameters and execute the query
$query->execute(array(':msg_a' => $msg_a, ':msg_b' => $msg_b));
// fetch the resultset
$rows = $query->fetchall(PDO::FETCH_ASSOC);