bool InsertOK;
InsertOK = false;
do
{
    Num = rnd.Next(0, 100000);
    sql = "select id from TableName where Number='" + Num + "'";
    if (读取不到此记录)
    {
        执行("insert into TableName(Number) values('" + Num+"')");
        InsertOK = true;
    }
} while (!InsertOK);