Type in date search field in the format dd / mm / yyyy and search the database in the format YYYY-mm-dd

In MySQL there is the STR_TO_DATE function, which receives as its parameter string of date and converts to a valid date in the SQL query:

SELECT STR_TO_DATE("01/12/2018", '%d/%m/%Y')

Returns: 2018-12-01

$data = substr($obj->getData(), 8, 2);
$data .= "/";
$data .= substr($obj->getData(), 5, 2);
$data .= "/";
$data .= substr($obj->getData(), 0, 4);