MySQL convert date string to Unix timestamp

Here's an example of how to convert DATETIME to UNIX timestamp:
SELECT UNIX_TIMESTAMP(STR_TO_DATE('Apr 15 2012 12:00AM', '%M %d %Y %h:%i%p'))

Here's an example of how to change date format:
SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(STR_TO_DATE('Apr 15 2012 12:00AM', '%M %d %Y %h:%i%p')),'%m-%d-%Y %h:%i:%p')

Documentation: UNIX_TIMESTAMP, FROM_UNIXTIME

You will certainly have to use both STR_TO_DATE to convert your date to a MySQL standard date format, and UNIX_TIMESTAMP to get the timestamp from it.

Given the format of your date, something like

UNIX_TIMESTAMP(STR_TO_DATE(Sales.SalesDate, '%M %e %Y %h:%i%p'))

Will gives you a valid timestamp. Look the STR_TO_DATE documentation to have more information on the format string.

For current date just use UNIX_TIMESTAMP() in your MySQL query.