How to float long table in latex?

Question

When I am using longtable in a two-column article in latex, I need to first make the article one-column by using \onecolumn. But the longtable starts from the next page, so the current page has too much unnecessary space. so what should I do to remove this space by adding content of the next section after the table? Here is the snapshot of paper

---Some text ---

\onecolumn
\begin{longtable}{|p{1.5cm}|p{1.5cm}|p{3.5cm}|p{3.5cm}|p{3cm}|p{3.5cm}|}

Table text

\end{longtable}
\twocolumn

---some text---