Simple table with caption:

\begin{longtable}[]{@{}rlcl@{}}
\caption{Demonstration of simple table syntax.}\tabularnewline
\toprule
Right & Left & Center & Default \\ \addlinespace
\midrule
\endfirsthead
\toprule
Right & Left & Center & Default \\ \addlinespace
\midrule
\endhead
12 & 12 & 12 & 12 \\ \addlinespace
123 & 123 & 123 & 123 \\ \addlinespace
1 & 1 & 1 & 1 \\ \addlinespace
\bottomrule
\end{longtable}

Simple table without caption:

\begin{longtable}[]{@{}rlcl@{}}
\toprule
Right & Left & Center & Default \\ \addlinespace
\midrule
\endhead
12 & 12 & 12 & 12 \\ \addlinespace
123 & 123 & 123 & 123 \\ \addlinespace
1 & 1 & 1 & 1 \\ \addlinespace
\bottomrule
\end{longtable}

Simple table indented two spaces:

\begin{longtable}[]{@{}rlcl@{}}
\caption{Demonstration of simple table syntax.}\tabularnewline
\toprule
Right & Left & Center & Default \\ \addlinespace
\midrule
\endfirsthead
\toprule
Right & Left & Center & Default \\ \addlinespace
\midrule
\endhead
12 & 12 & 12 & 12 \\ \addlinespace
123 & 123 & 123 & 123 \\ \addlinespace
1 & 1 & 1 & 1 \\ \addlinespace
\bottomrule
\end{longtable}

Multiline table with caption:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\caption{Here's the caption. It may span multiple lines.}\tabularnewline
\toprule
Centered Header & Left Aligned & Right Aligned & Default
aligned \\ \addlinespace
\midrule
\endfirsthead
\toprule
Centered Header & Left Aligned & Right Aligned & Default
aligned \\ \addlinespace
\midrule
\endhead
First & row & 12.0 & Example of a row that spans multiple
lines. \\ \addlinespace
Second & row & 5.0 & Here's another one. Note the blank line between
rows. \\ \addlinespace
\bottomrule
\end{longtable}

Multiline table without caption:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\toprule
Centered Header & Left Aligned & Right Aligned & Default
aligned \\ \addlinespace
\midrule
\endhead
First & row & 12.0 & Example of a row that spans multiple
lines. \\ \addlinespace
Second & row & 5.0 & Here's another one. Note the blank line between
rows. \\ \addlinespace
\bottomrule
\end{longtable}

Table without column headers:

\begin{longtable}[]{@{}rlcr@{}}
\toprule
\endhead
12 & 12 & 12 & 12 \\ \addlinespace
123 & 123 & 123 & 123 \\ \addlinespace
1 & 1 & 1 & 1 \\ \addlinespace
\bottomrule
\end{longtable}

Multiline table without column headers:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\toprule
\endhead
First & row & 12.0 & Example of a row that spans multiple
lines. \\ \addlinespace
Second & row & 5.0 & Here's another one. Note the blank line between
rows. \\ \addlinespace
\bottomrule
\end{longtable}