php SQL之where语句生成器

//生成where字符串 
function get_where($arg = null) { 
foreach ((array)$arg as $key => $val) { 
if(is_int($key)) { 
$where .= " $val "; 
}else { 
if(is_string($val)) { 
if($val === null) { 
$where .= " and $key is null "; 
}else { 
$where .= " and $key = '$val' "; 
} 
}elseif(is_array($val)) { 
foreach ($val as $v) { 
if(is_string($v)) { 
$in .= $in ? ",'$v'" : "'$v'"; 
}else { 
$in .= $in ? ",$v" : "$v"; 
} 
} 
$where .= " and $key in ($in)"; 
}else { 
$where .= " and $key = $val "; 
} 
} 
} 
return $where; 
}