Selecting The First Record In A Join?

I have one table like this:

Code:
CREATE TABLE DlIndexTable
(SessionStartTime DATETIME NOT NULL PRIMARY KEY, SchemaID INTEGER NOT NULL,
DLBaseRate REAL NOT NULL)

and one like so:

Code:
CREATE TABLE DlTextDataTable (
SessionStartTime DATETIME NOT NULL REFERENCES DlIndexTable,
ChTimestamp FLOAT NOT NULL, Channel01data VARCHAR (255),
Channel02data VARCHAR (255), ... , Channel16data VARCHAR (255),
CONSTRAINT TxtDatPriKey PRIMARY KEY (SessionStartTime, ChTimestamp))

I want to get some combined data from both tables, so right now I am joining them at the SessionStartTime column, which is a primary key in the first and a foreign key in the second table, something like this:

Code:
SELECT DlIndexTable.SessionStartTime, DlTextDataTable.Channel01data
FROM DlIndexTable
LEFT JOIN DlTextDataTable
ON DlIndexTable.SessionStartTime = DlTextDataTable.SessionStartTime
WHERE DlIndexTable.SessionStartTime BETWEEN '2006-10-13 16:40:08.790' AND '2012-03-01 17:54:30.930'
ORDER BY DlIndexTable.SessionStartTime, DlTextDataTable.ChTimestamp

The trouble is that this query, exactly as requested, gives me all the entries from the second table matching the first, while I really would like to pick just one row (preferably, the first chronologically - by ChTimestamp) so that the first column (SessionStartTime) has distinct entries in the resulting table. What would be the simplest way of doing that? Performance is not a big priority over simplicity since the first table could have only a few hundred rows (maybe a couple of thousand), while the second will be real tiny.