Загадка!

$dydy = array(); 
$sql2 = "SELECT * FROM catalog1 WHERE 
city IN('скайп')"; 
$result2 = mysql_query($sql2) or die(mysql_error()); 
while($row2 = mysql_fetch_array($result2, MYSQL_NUM)){   
$dydy[] = $row2; 
} 
echo "<pre>";print_r($dydy);echo "<pre>"; 
echo $sql2,'<br>';

$dydy = array(); 
$sql2 = "SELECT * FROM catalog1 WHERE 
country IN('Свердловская область')"; 
$result2 = mysql_query($sql2) or die(mysql_error()); 
while($row2 = mysql_fetch_array($result2, MYSQL_NUM)){   
$dydy[] = $row2; 
}
echo "<pre>";print_r($dydy);echo "<pre>"; 
echo $sql2,'<br>';

$dydy = array(); 
$sql2 = "SELECT * FROM catalog1 WHERE 
country IN('Свердловская область, скайп')"; 
$result2 = mysql_query($sql2) or die(mysql_error()); 
while($row2 = mysql_fetch_array($result2, MYSQL_NUM)){   
$dydy[] = $row2; 
} 
echo "<pre>";print_r($dydy);echo "<pre>"; 
echo $sql2,'<br>';

<?php
 
$country = ['Свердловская область','скайп'];
//$country = ['Свердловская область'];
//$country = [];
$sql = "... country IN(". 
    (!strlen($tmp=implode("','",$country)) ? 'NULL' : "'{$tmp}'")
.") ...";
 
echo $sql;

$values = ['val1', 'val2', 'val3'];
 
foreach($values as $k => $v)
    $values[$k] = "'$v'";
 
$in = implode(',', $values);