When comparing DATEs with constant strings, MySQL first tries to convert
the constant string to date and do the comparison as DATETIME. In case
the conversion fails, MySQL will still execute the comparison but as
string which is likely not what was intended in the first place.

Fix is to always compare as DATETIME, and in case the constant string is
invalid date, to return error.

Change-Id: I0d1e35c4d7af1f8082760c6a93aab3861c23ab40