autocmd FileType sql nmap <buffer> <leader>t :<C-U>w \| call Send_to_Tmux("\\i ".expand("%")."\n")<CR>
With this command, if you're editing an SQL file in a Tmux session, run
<leader>t from normal mode, and your file will be read into the session and window of your choice. If there's a
psql session listening there, you've got a fast way to iterate on an SQL statement from Vim.
The command even writes the file for you before sending the SQL.