I think we could split the first <programlisting> into two parts:
- CREATE/INSERT statements
- Exclusive PSQL commands. Then here we could explain that NULL will be
displayed depending on the client program used.
<para>
The following <literal>CREATE TABLE</literal> and <literal>INSERT</literal>
SQL commands can be executed in any SQL client to create and populate
the persistent table used in the examples below.
</para>
<programlisting>
CREATE TABLE null_examples ( ... );
INSERT INTO null_examples
</programlisting>
<para>
The <literal>\pset</literal> commands require the use of <application>psql</application>
as the client program; they make the resulting output a bit easier to read and do not
impact any behaviors described herein. If you do not use <application>psql</application>
to execute the commands, resulting NULL values may appear as <NULL>, [Null], or any other variation.
</para>
<programlisting>
-- This makes null values print as "Null" in the output instead of an empty string.
-- Note: SQL text output uses "NULL" and JSON text output uses "null"
\pset null Null
-- These cause boolean values to print as true/false instead of t/f.
\pset display_true true
\pset display_false false
-- Removes the row count footer that prints by default.
\pset footer off
</programlisting>
<para>
The examples also omit any transactional command output when
transactions are used. Instead, each transaction gets its own display block.
Some outputs have <literal>/* ... */</literal> comments and newlines
manually added for clarity.
</para>
