单列数组（getYieldValues）

普通查询

$db = Be::getDb(); 

$sql = 'SELECT name FROM user WHERE age<18 AND sex=\'女\'';
$names = $db->getYieldValues($sql);

foreach ($names as $name) {
   // $name;
}

占位符查询

$db = Be::getDb(); 

$sql = 'SELECT name FROM user WHERE age<? AND sex=?';
$names = $db->getYieldValues($sql,  [18, '女']);