Avoid lots of \text{} commands in formulas

Question

I am working on typing a document with a lot of formulas which have words in them. I know I can use \text{} from the AMS package to make the word appear normally in the equation, but I was wondering if there was a less cumbersome way to do this when I have many words in the same formula. Is there a way to set all the characters in a formula to appear normally or else some less obtrusive way to accomplish this?

Example:

$\sigma_{\text{type}=\text{'single'} \, \text{AND} \, \text{price} < 20}(\text{Room})$

Answer 1

Based on this answer, here we use * instead of < which is frequently used in math mode.

Just add your text in math mode like *text*, if you which to use character * outside math mode you can do it with the restoration of its code number inside a group.

MWE

\documentclass{article}
\usepackage{amsmath}

\catcode`\*=13
\begingroup
\lccode`\~=`\*
\lowercase{\endgroup
  \def~#1*}{\text{#1}}

\begin{document}

$\sigma_{*type*=*'single'* \, *AND* \, *price* < 20}(*Room*)$

{\catcode`\*=12 text*} 

$\sigma_{*type*=*'single'* \, *AND* \, *price* < 20}(*Room*)$

\end{document}    

Update

Thanks to @egreg suggestion replacing \catcode with \mathcode to avoid changing code number of * every time outside math mode

\documentclass{article}
\usepackage{amsmath}

\mathcode`*="8000
\begingroup
\lccode`\~=`\*
\lowercase{\endgroup
  \def~#1*}{\text{#1}}

\begin{document}

$\sigma_{*type*=*'single'* \, *AND* \, *price* < 20}(*Room*)$

text* 

$\sigma_{*type*=*'single'* \, *AND* \, *price* < 20}(*Room*)$

\end{document}   

Output

Answer 2

You can create new command by \newcommand (or \renewcommand if they exist) to make text subscripts. I think something like \newcommand{\pippo}[1]{{}_\text{#1}} could work.. (I cannot try now, sorry)

Answer 3

Some things appear the same (or almost the same) in text and math modes, so for this example you could simply use

$\sigma_{\text{type = `single' AND price $<$ 20}}$(Room)

or

$\sigma_{\text{type$\strut =\strut$`single' AND price$\strut <20$}}$(Room)