I want to have double lines in the top row in my tables in lyx. I searched through the site but could not find how to do this.
Due to the nature of the setup in LyX, you could insert a ERT with
\hline in the first cell of the table:
Nothing should be placed before it, but you can put content after it. The output is fairly horrible though:
It is advisable to use the "Formal" table border setting instead (Edit > Table Settings... > Borders > Style > Formal), since it uses
booktabs in the presentation. This package uses
\bottomrule to emphasize the top/bottom of the table, setting it with a thicker rule.