How to search in datatable by datetime

Here is my complete example, tested in VS2017 with .NET 4.5.1:

using System;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.Windows.Forms;

namespace TestForm1
{
    /// <summary>
    /// Codeproject DataTable
    /// </summary>
    public partial class Form1 : Form
    {
        DataTable dt1 = new DataTable();

        public Form1()
        {
            InitializeComponent();
            Test();
        }

        private void Test()
        {
            // Add columns
            dt1.Columns.Add("Shift Start", typeof(DateTime));
            dt1.Columns.Add("employee_id", typeof(string));
            dt1.Columns.Add("employee_name", typeof(string));
            dt1.Columns.Add("Shift End", typeof(DateTime));

            DateTime d = DateTime.Now;

            // Add test data
            dt1.Rows.Add(d.AddMinutes(-10), "1", "PRINCE", d.AddMinutes(-1));
            dt1.Rows.Add(d, "2", "KING", d.AddMinutes(2));
            dt1.Rows.Add(d.AddMinutes(1), "3", "PAUPER", d.AddMinutes(2));

            IEnumerable<DataRow> selectedRows = dt1.AsEnumerable()
                .Where(row => (row.Field<DateTime>("Shift Start") <= d) && (d <= row.Field<DateTime>("Shift End")));

            foreach (DataRow row in selectedRows)
            {
                Console.WriteLine("{0}, {1}", row[0], row[1]);
            }
        }
    }
}

Nothing to do with your question but never have spaces in column or table names - same goes for file and folder names - just sayin :-)

Quote:

the problem is i want to select all the records within this date and time. I tried the following code but not working.

You want to know which people were working at a given datetime (dt).
It mean people with [Shift Start] before dt and [Shift End] after dt. the problem is than you did it in reverse, you query is looking for people that [Shift Start] after dt and [Shift End] before dt.

expression = "[Shift Start] < #4/12/2018 " + strD + "# AND [Shift End] > #4/12/2018 " + strD + "#";

Not your question, but another problem you have.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[^]
SQL Injection[^]
SQL Injection Attacks by Example[^]
PHP: SQL Injection - Manual[^]
SQL Injection Prevention Cheat Sheet - OWASP[^]
How can I explain SQL injection without technical jargon? - Information Security Stack Exchange[^]

string str=4/12/2018 11:00:00
if your searching in sql table
select * from table where endshit='4/12/2018 11:00:00';