<tip>

<para>

Because JSON containment is nested, an appropriate query can skip

explicit selection of sub-objects. As an example, suppose that we have

a <structfield>doc</> column containing objects at the top level, with

most objects containing <literal>tags</> fields that contain arrays of

sub-objects. This query finds entries in which sub-objects containing

both <literal>"term":"paris"</> and <literal>"term":"food"</> appear,

while ignoring any such keys outside the <literal>tags</> array:

<programlisting>

SELECT doc-&gt;'site_name' FROM websites

WHERE doc @&gt; '{"tags":[{"term":"paris"}, {"term":"food"}]}';

</programlisting>

One could accomplish the same thing with, say,

<programlisting>

SELECT doc-&gt;'site_name' FROM websites

WHERE doc-&gt;'tags' @&gt; '[{"term":"paris"}, {"term":"food"}]';

</programlisting>

but that approach is less flexible, and often less efficient as well.

</para>

<para>

On the other hand, the JSON existence operator is not nested: it will

only look for the specified key or array element at top level of the

JSON value.

</para>

</tip>