day(param) - Returns the day of the month of date/timestamp, or day component of interval
Synonyms: dayofmonth
param can be one of:
1. A string in the format of 'yyyy-MM-dd HH:mm:ss' or 'yyyy-MM-dd'.
2. A date value
3. A timestamp value
4. A day-time interval valueExample:
   > SELECT day('2009-07-30') FROM src LIMIT 1;
  30
