由于对于不同的语言和环境有多种答案，这里有一个标准ANSISQL的答案。

在标准SQL中，它非常简单

(StartDate1, EndDate1) overlaps (StartDate2, EndDate2)

假设所有四列都是DATE或TIMESTAMP列。如果两个范围至少有一天相同（假设DATE值），则返回true

（但并非所有DBMS产品都支持此功能）

在PostgreSQL中，使用日期范围也很容易测试是否包含

daterange(StartDate1, EndDate1) @> daterange(StartDate2, EndDate2)

如果第二个范围完全包含在第一个范围中（与“重叠”不同），则上述值返回真

我认为，在以下情况下，两个范围重叠就足够了：

(StartDate1 <= EndDate2) and (StartDate2 <= EndDate1)

这里有一个可以在本地使用的通用方法。

    // Takes a list and returns all records that have overlapping time ranges.
    public static IEnumerable<T> GetOverlappedTimes<T>(IEnumerable<T> list, Func<T, bool> filter, Func<T,DateTime> start, Func<T, DateTime> end)
    {
        // Selects all records that match filter() on left side and returns all records on right side that overlap.
        var overlap = from t1 in list
                      where filter(t1)
                      from t2 in list
                      where !object.Equals(t1, t2) // Don't match the same record on right side.
                      let in1 = start(t1)
                      let out1 = end(t1)
                      let in2 = start(t2)
                      let out2 = end(t2)
                      where in1 <= out2 && out1 >= in2
                      let totover = GetMins(in1, out1, in2, out2)
                      select t2;

        return overlap;
    }

    public static void TestOverlap()
    {
        var tl1 = new TempTimeEntry() { ID = 1, Name = "Bill", In = "1/1/08 1:00pm".ToDate(), Out = "1/1/08 4:00pm".ToDate() };
        var tl2 = new TempTimeEntry() { ID = 2, Name = "John", In = "1/1/08 5:00pm".ToDate(), Out = "1/1/08 6:00pm".ToDate() };
        var tl3 = new TempTimeEntry() { ID = 3, Name = "Lisa", In = "1/1/08 7:00pm".ToDate(), Out = "1/1/08 9:00pm".ToDate() };
        var tl4 = new TempTimeEntry() { ID = 4, Name = "Joe", In = "1/1/08 3:00pm".ToDate(), Out = "1/1/08 8:00pm".ToDate() };
        var tl5 = new TempTimeEntry() { ID = 1, Name = "Bill", In = "1/1/08 8:01pm".ToDate(), Out = "1/1/08 8:00pm".ToDate() };
        var list = new List<TempTimeEntry>() { tl1, tl2, tl3, tl4, tl5 };
        var overlap = GetOverlappedTimes(list, (TempTimeEntry t1)=>t1.ID==1, (TempTimeEntry tIn) => tIn.In, (TempTimeEntry tOut) => tOut.Out);

        Console.WriteLine("\nRecords overlap:");
        foreach (var tl in overlap)
            Console.WriteLine("Name:{0} T1In:{1} T1Out:{2}", tl.Name, tl.In, tl.Out);
        Console.WriteLine("Done");

        /*  Output:
            Records overlap:
            Name:Joe T1In:1/1/2008 3:00:00 PM T1Out:1/1/2008 8:00:00 PM
            Name:Lisa T1In:1/1/2008 7:00:00 PM T1Out:1/1/2008 9:00:00 PM
            Done
         */
    }

这是我的Java解决方案，它也适用于无限区间

private Boolean overlap (Timestamp startA, Timestamp endA,
                         Timestamp startB, Timestamp endB)
{
    return (endB == null || startA == null || !startA.after(endB))
        && (endA == null || startB == null || !endA.before(startB));
}

我会的

StartDate1.IsBetween(StartDate2, EndDate2) || EndDate1.IsBetween(StartDate2, EndDate2)

IsBetween是这样的

    public static bool IsBetween(this DateTime value, DateTime left, DateTime right) {
        return (value > left && value < right) || (value < left && value > right);
    }

答案对我来说太简单了，所以我创建了一个更通用的动态SQL语句，用于检查某人是否有重叠的日期。

SELECT DISTINCT T1.EmpID
FROM Table1 T1
INNER JOIN Table2 T2 ON T1.EmpID = T2.EmpID 
    AND T1.JobID <> T2.JobID
    AND (
        (T1.DateFrom >= T2.DateFrom AND T1.dateFrom <= T2.DateTo) 
        OR (T1.DateTo >= T2.DateFrom AND T1.DateTo <= T2.DateTo)
        OR (T1.DateFrom < T2.DateFrom AND T1.DateTo IS NULL)
    )
    AND NOT (T1.DateFrom = T2.DateFrom)