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Doc: copy-edit "jsonb Indexing" section.

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The patch introducing jsonpath dropped a para about that between
two related examples, and didn't bother updating the introductory
sentences that it falsified.  The grammar was pretty shaky as well.
This commit is contained in:
Tom Lane 2022-06-08 12:01:51 -04:00
parent b46e8a83e9
commit abed46aea4
1 changed files with 32 additions and 22 deletions
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54
doc/src/sgml/json.sgml
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@ -415,9 +415,10 @@ SELECT doc->'site_name' FROM websites
</para>
<para>
The default GIN operator class for <type>jsonb</type> supports queries with
top-level key-exists operators <literal>?</literal>, <literal>?&amp;</literal>
and <literal>?|</literal> operators and path/value-exists operator
<literal>@&gt;</literal>.
the key-exists operators <literal>?</literal>, <literal>?|</literal>
and <literal>?&amp;</literal>, the containment operator
<literal>@&gt;</literal>, and the <type>jsonpath</type> match
operators <literal>@?</literal> and <literal>@@</literal>.
(For details of the semantics that these operators
implement, see <xref linkend="functions-jsonb-op-table"/>.)
An example of creating an index with this operator class is:
@ -425,7 +426,8 @@ SELECT doc-&gt;'site_name' FROM websites
CREATE INDEX idxgin ON api USING GIN (jdoc);
</programlisting>
The non-default GIN operator class <literal>jsonb_path_ops</literal>
supports indexing the <literal>@&gt;</literal> operator only.
does not support the key-exists operators, but it does support
<literal>@&gt;</literal>, <literal>@?</literal> and <literal>@@</literal>.
An example of creating an index with this operator class is:
<programlisting>
CREATE INDEX idxginp ON api USING GIN (jdoc jsonb_path_ops);
@ -482,22 +484,7 @@ CREATE INDEX idxgintags ON api USING GIN ((jdoc -&gt; 'tags'));
(More information on expression indexes can be found in <xref
linkend="indexes-expressional"/>.)
</para>
<para>
Also, GIN index supports <literal>@@</literal> and <literal>@?</literal>
operators, which perform <literal>jsonpath</literal> matching.
<programlisting>
SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @@ '$.tags[*] == "qui"';
</programlisting>
<programlisting>
SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @? '$.tags[*] ? (@ == "qui")';
</programlisting>
GIN index extracts statements of following form out of
<literal>jsonpath</literal>: <replaceable>accessors_chain</replaceable> = <replaceable>const</replaceable>.
Accessors chain may consist of <literal>.key</literal>,
<literal>[*]</literal>, and <literal>[<replaceable>index</replaceable>]</literal> accessors.
<literal>jsonb_ops</literal> additionally supports <literal>.*</literal>
and <literal>.**</literal> accessors.
</para>
<para>
Another approach to querying is to exploit containment, for example:
<programlisting>
@ -514,10 +501,33 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
index.
</para>
<para>
GIN indexes also support the <literal>@?</literal>
and <literal>@@</literal> operators, which
perform <type>jsonpath</type> matching. Examples are
<programlisting>
SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @? '$.tags[*] ? (@ == "qui")';
</programlisting>
<programlisting>
SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @@ '$.tags[*] == "qui"';
</programlisting>
For these operators, a GIN index extracts clauses of the form
<literal><replaceable>accessors_chain</replaceable>
= <replaceable>constant</replaceable></literal> out of
the <type>jsonpath</type> pattern, and does the index search based on
the keys and values mentioned in these clauses. The accessors chain
may include <literal>.<replaceable>key</replaceable></literal>,
<literal>[*]</literal>,
and <literal>[<replaceable>index</replaceable>]</literal> accessors.
The <literal>jsonb_ops</literal> operator class also
supports <literal>.*</literal> and <literal>.**</literal> accessors,
but the <literal>jsonb_path_ops</literal> operator class does not.
</para>
<para>
Although the <literal>jsonb_path_ops</literal> operator class supports
only queries with the <literal>@&gt;</literal>, <literal>@@</literal>
and <literal>@?</literal> operators, it has notable
only queries with the <literal>@&gt;</literal>, <literal>@?</literal>
and <literal>@@</literal> operators, it has notable
performance advantages over the default operator
class <literal>jsonb_ops</literal>. A <literal>jsonb_path_ops</literal>
index is usually much smaller than a <literal>jsonb_ops</literal>