This codes a bit tough to trace since you don't have indentation here.
The CSV is logically a two dimensional array or a collection of collection. So you could just split the readTextFile entries up into a collection. Problem is I have no idea what is in that collection, so I can't really tell you what to do with it.
You can write a simple CSV interpreter by simply splitting the string on the delimiter. A good one would need to also determine enclosure characters since a string in a csv file could include the delimiter character as well. If its something like a CSV of numbers, than a simple tokenizer on the delimiter would be sufficient. Collections can then determine min and max very easily using the Collections.min and Collections.max methods.
As of PHP 5.5, the MySQL library has been officially deprecated. It is recommended to move to either MySQLi or PDO libraries for your mysql connectivity. See here for help choosing which interface you prefer: http://php.net/manual/en/mysqlinfo.api.choosing.php