The etags program
<https://www.gnu.org/software/emacs/manual/html_node/emacs/Tags-Tables.html>
creates a text file listing the locations of symbol definitions, in a
form that can be used to navigate your way around a complex project.

As far as I know, though, no-one has thought of putting the symbol
definitions into something like an SQLite database, for more
convenient lookup.

In my custom Emacs definitions <https://gitlab.com/ldo/emacs-prefs>, I
wrote a Python program, called “project-tags”, which creates such a
database, lets you keep it up to date, and of course perform lookups
on it. I provide a command “find-def” for Emacs (in project-tags.el),
which lets you invoke the lookup function of the project-tags program
to obtain the definition of a selected symbol in the same project as
the current source file, and go straight to there. If it finds more
than one definition, then it puts up a list of the alternatives, for
you to select from.

A “project” is identified by default by the presence of a .git
subdirectory in its top-level directory. Alternatively, you can define
an arbitrary directory as the root of a project -- e.g. if you index
all the symbols in /usr/include, then that makes it easy to find where
system APIs are defined. The details of how to set this all up are
explained in the enclosed man page for project-tags.