Typically, if you were writing your hypothetical sql client in rc shell, you'd implement an interface that looks something like:

    <>/mnt/sql/clone{
        echo 'SELECT * from ...' >[1=0]
        cat /mnt/sql/^`{read}^/data # or awk, or whatever
    }

This is also roughly how webfs works. Making network connections from the shell follows the same pattern. So, for that matter, does making network connections from C, just the file descriptor management is in C.