为什么要关闭数据库连接，可以不关闭吗？

<span>for</span> (<span>int</span> i = 0; i < 10000; i++)
{
    SqlConnection conn = <span>new</span> SqlConnection(<span>@"Data Source=.\SQLEXPRESS;
                AttachDbFilename="</span><span>"E:\DB\NORTHWND.mdf"</span><span>";
                Integrated Security=True;Connect Timeout=30;User Instance=True"</span>);

    conn.Open();
    Console.WriteLine(<span>"打开了{0}个连接"</span>, i);
}

SqlConnection conn = <span>new</span> SqlConnection(<span>@"Data Source=.\SQLEXPRESS;
                    AttachDbFilename="</span><span>"E:\DB\NORTHWND.mdf"</span><span>";
                    Integrated Security=True;Connect Timeout=30;User Instance=True"</span>);
conn.Open();
Parallel.For(1, 9999, (id) =>
{
    ExecuteCommand(conn, id);
});

 

<span>private</span> <span>static</span> <span>void</span> ExecuteCommand(SqlConnection conn, <span>int</span> id)
{
    Console.WriteLine(<span>"正在执行."</span> + id);

    Thread.Sleep(100);

    SqlCommand cmd = <span>new</span> SqlCommand(
       <span>string</span>.Format(<span>"Insert into Nums values('{0}') "</span>, id), conn);

    cmd.ExecuteNonQuery();
}

<span>if</span> (conn.State != System.Data.ConnectionState.Open)
    conn.Open();

<span>private</span> <span>static</span> <span>object</span> syncObj = <span>new</span> <span>object</span>();

<span>private</span> <span>static</span> <span>void</span> ExecuteCommand(SqlConnection conn, <span>int</span> id)

{

    <span>lock</span> (syncObj)

    {

        <span>if</span> (conn.State != System.Data.ConnectionState.Open)

            conn.Open();

        Console.WriteLine("<span>正在执行..</span>" + id);

        Thread.Sleep(100);

        SqlCommand cmd = <span>new</span> SqlCommand(

           <span>string</span>.Format("<span>Insert into Nums values('{0}') </span>", id), conn);

        cmd.ExecuteNonQuery();

    }

}

<pre class="brush:php;toolbar:false;">Parallel.For(1, Int32.MaxValue, (id) =>

            {

                ExecuteCommand(conn, id);

            });