With respect to the original question, you're ignoring the funny stuff: the conditionals.
IF DateTo IS NOT NULL THEN
SET @DateTo = (SELECT CASE WHEN DateTo = '' THEN NOW() ELSE CAST(DateTo AS DATETIME) END);
ELSE SET @DateTo = NOW();
I'd go for something like
SET DateTo = COALESCE(DateTo, '');
SET @DateTo = (SELECT CASE WHEN DateTo = '' THEN NOW() ELSE CAST(DateTo AS DATETIME) END);
However, passing date as string seems broken to me, at least when you want to call it from program. It puts you on the mercy of formatting/parsing issues and locales and timezones (unless your server is collocated and properly set up) and what else.
That all said, I gladly repeat myself:
I find the idea perverted, because of
- the need to have some DB around
- inefficiency (round trip to DB)
- exposing yourself to various DB quirks
