Merging trips to the same location with overlapping dates

I have a SQLite database that only contains the holidays for 1 user.

I have a new Trip object (newTrip) that has a StartDate(long unix time) and an EndDate(long unix time) and the trip Iso3Code(string) for the location.

I need to retrieve from the database all existing Trips that can be merged with the newTrip. A trip can be merged if the dates of the new trip fall at the same time of the existing trips or on the day before or after the existing trips and have the same Iso2Code`.

So far I have this:

public static List GetTripsThatCanBeMerged(Trip trip)
{
    //ignore times - just get for that date and get the date before for the start date and the day after for the end data, as the day before and after can be merged.
    DateTime startDate = DateTimeHelper.UnixDateToDateTime(trip.StartDate).Date.AddDays(-1);
    DateTime endDate = DateTimeHelper.UnixDateToDateTime(trip.EndDate).Date.AddDays(1);

    //now convert back to unix
    long startDateUnix = DateTimeHelper.DateTimeToUnixTimestamp(startDate);
    long endDateUnix = DateTimeHelper.DateTimeToUnixTimestamp(endDate);

    List trips = null;

    using (SQLiteConnection conn = new SQLiteConnection(new SQLitePlatformWinRT(), _sqliteDatabasePath))
    {
        trips = conn.GetAllWithChildren(p => 
            ((p.StartDate >= startDateUnix && p.StartDate = startDateUnix && p.EndDate = p.StartDate && endDateUnix <= p.EndDate))) &&
            p.Iso3Code == trip.Iso3Code
            , true);
    }

    return trips;
}

I think this is correct but can anyone suggest a less complex way of doing it, or see any errors.

Let's look at this line:

(p.StartDate = p.StartDate && endDateUnix <= p.EndDate))

If p.StartDate = p.StartDate is redundant.

So the first part of the query can be written as

(p.StartDate >= startDateUnix && p.StartDate = startDateUnix && p.EndDate <= endDateUnix) || 
(p.StartDate <= startDateUnix && endDateUnix <= p.EndDate)

I would recommend rewriting the first two conditions as follows:

(startDateUnix <= p.StartDate && p.StartDate <= endDateUnix) || 
(startDateUnix <= p.EndDate && p.EndDate <= endDateUnix)

I find it easier to see at a glance that it's saying that p.StartDate lies within [startDateUnix, endDateUnix] (similarly for p.EndDate).

Another way to test for overlapping intervals is

p.StartDate <= endDateUnix && startDateUnix <= p.EndDate

StackExchange Code Review Q#129204, answer score: 2