Convert date string into MySQL Date format

PHP data type conversion

$origin = '97.09.27';
$dt = preg_split('/\./', $origin);
$mysqlDate = ((int)$dt[0] + 1911).'-'.$dt[1].'-'.dt[2];

1. preg_split has at least 2 parameters:
   1) '/\./' -- regular expression pattern
   2) $origin -- the string to be splited
   it use regular expression pattern to separate the string into array

2. convert string to number (coersion)
   use (int), (float), (long) before string to convert a string into number
   (int)$string

3. merge number and string together to generate a new string
   the string concatenate operator "." join several numbers/strings into a single string