Fundamental Index Question

[Brandon Shuey]

My question is how does mysql use indexing in the following example:

cDate=Date_Format(Date_Time,'%Y-%m-%d') just for purposes of this example

CREATE TABLE tblLogins(
	indxLogin		int not null,
	dDate 		Date_Time not null,
	cDate			Date not null,
	LoginTried		char(20),
	PasswdTried		char(20),
	PRIMARY KEY 	(indxLogin),
	INDEX dateIndx 	(cDate,LoginTried)
);
SELECT dDate,LoginTried,Count(*) FROM tblLogins WHERE dDate >='1999-05-01 00:00:00' and
dDate < '1999-05-02 00:00:00' GROUP BY
dDate,LoginTried;

Will mysql use the dateIndx?  Shouldn't dateIndx be sorted by dDate, LoginTried and
provide extremely quick results by quickly
finding the matching cDate and performing the group count on only those records?  Am I
thinking of the index in the wrong way?

Brandon Shuey
WebCentric Inc.
[phone]
brandon@stripped