It's almost a year later, but as the OP has not yet accepted an answer, I still see my chance :-)
In the following, I use the same basic principle as in my other answer, that is, employ listings moredelim=** option to define delimiters, which styles then apply on top of all other formattings, so that the syntax formatting is kept.
However, instead of being limited to a standard font command for the delimiter style, I now use an lrbox to grab the content of the current group. The resulting box holds the (syntax-formatted) output of listings, which can be used to implement more fancy highlighting styles.
In the example code, the implementation of the \btHL command employs TikZ to typeset the lrbox into a TikZ node. Additional TikZ/PGF options to both, the tikzpicture and the node can be given in the optional argument (such as \btHL[fill=red!20,draw=red]), which provides for pretty flexible highlighters.
(Note: when the optional argument is used inside some listings argument, the whole \btHL[<key>=<value>,...] command has to be put into curly braces in order to not confuse the listings key=value parser.)
The \btHL command can as well be used inside normal text. It does, however, not work across line breaks, which is a possible disadvantage compared to the approach that culminated from Bens answer. Insides of listings, however, this usually is not an issue.
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{listings,xcolor,beramono}
\usepackage{tikz}
\makeatletter
\newenvironment{btHighlight}[1][]
{\begingroup\tikzset{bt@Highlight@par/.style={#1}}\begin{lrbox}{\@tempboxa}}
{\end{lrbox}\bt@HL@box[bt@Highlight@par]{\@tempboxa}\endgroup}
\newcommand\btHL[1][]{%
\begin{btHighlight}[#1]\bgroup\aftergroup\bt@HL@endenv%
}
\def\bt@HL@endenv{%
\end{btHighlight}%
\egroup
}
\newcommand{\bt@HL@box}[2][]{%
\tikz[#1]{%
\pgfpathrectangle{\pgfpoint{1pt}{0pt}}{\pgfpoint{\wd #2}{\ht #2}}%
\pgfusepath{use as bounding box}%
\node[anchor=base west, fill=orange!30,outer sep=0pt,inner xsep=1pt, inner ysep=0pt, rounded corners=3pt, minimum height=\ht\strutbox+1pt,#1]{\raisebox{1pt}{\strut}\strut\usebox{#2}};
}%
}
\makeatother
\lstdefinestyle{SQL}{
language={SQL},basicstyle=\ttfamily,
moredelim=**[is][\btHL]{`}{`},
moredelim=**[is][{\btHL[fill=green!30,draw=red,dashed,thin]}]{@}{@},
}
\begin{document}
A listing with {\btHL highlighting of all \textbf{important} elements} looks as follows:
\begin{lstlisting}[style=SQL]
SELECT name, password `FROM` users @WHERE@ name=@UNION SELECT@
\end{lstlisting}
Here is a proposal using tcolorbox. Colors, shadows, etc. can be adjusted to your liking. You may replace style=tcblatex by any listings setting you want to have as default for your environment.
\documentclass[twocolumn]{article}
\usepackage{lipsum}
\usepackage[most]{tcolorbox}
\newenvironment{CenteredShadowboxListing}[1][]{%
\tcbset{listing options={style=tcblatex,#1}}\tcbwritetemp}%
{\endtcbwritetemp%
\tcbox[enhanced,arc=0pt,outer arc=0pt,top=1mm,bottom=1mm,left=1mm,right=1mm,
boxrule=0.6pt,drop fuzzy shadow,before=\begin{center},after=\end{center}]%
{\tcbusetemplisting}}
\begin{document}
\lipsum[4]
\begin{CenteredShadowboxListing}
line of code
line of code
\end{CenteredShadowboxListing}
\lipsum[4]
\end{document}
UPDATE: With tcolorbox version 2.41 of 2013/07/23, the code to typset the example above can be written more compact with the same result:
\documentclass[twocolumn]{article}
\usepackage{lipsum}
\usepackage[most]{tcolorbox}% version 2.41 or newer
\newtcblisting{CenteredShadowboxListing}[1][]{%
listing options={style=tcblatex,#1},hbox,listing only,
enhanced,arc=0pt,outer arc=0pt,top=1mm,bottom=1mm,left=1mm,right=1mm,
boxrule=0.6pt,drop fuzzy shadow,before=\begin{center},after=\end{center}}
\begin{document}
\lipsum[4]
\begin{CenteredShadowboxListing}
line of code
line of code
\end{CenteredShadowboxListing}
\lipsum[4]
\end{document}
Best Answer
Use
breaklines=true: