PHP MySql双引号比单引号

Question

I was reading a book about PHP and saw this code for inserting records. I do not understand a specific expression in the default case of the ternary operator. More specifically:

"'$v',"

Did the author make a mistake using single quotes (') and what he really meant were the backticks(`) to quote a soecial mysql expression? Why would you use single quotes and then double quotes on a variable?

According to the mysql documentation :

"The identifier quote character is the backtick (“`”): " http://dev.mysql.com/doc/refman/5.0/en/identifiers.html

public function insertRecords($table, $data){
    //setup some variables for fields and values
    $fields = "";
    $values = "";

    //populate them
    foreach($data as $f => $v){
        $fields .= "`$f`,";
        $values .= (is_numeric($v) && (intval($v) == $v)) ? $v . "," : "'$v',";
    }
}

Answer 1

double quotes signify that it's a string and the single quotes are part of a string. inside double quotes variables are evaluated so the string will contain the value of the variable 'vValue' not '$v'