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doc: Fix spacing in verbatim environments

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This commit is contained in:
Peter Eisentraut
2014-07-08 11:39:07 -04:00
parent 6048896e4c
commit 53166fe248
7 changed files with 96 additions and 95 deletions
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64
doc/src/sgml/json.sgml
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@ -163,7 +163,7 @@
</para>
<para>
The following are all valid <type>json</> (or <type>jsonb</>) expressions:
<programlisting>
<programlisting>
-- Simple scalar/primitive value
-- Primitive values can be numbers, quoted strings, true, false, or null
SELECT '5'::json;
@ -177,7 +177,7 @@ SELECT '{"bar": "baz", "balance": 7.77, "active": false}'::json;
-- Arrays and objects can be nested arbitrarily
SELECT '{"foo": [true, "bar"], "tags": {"a": 1, "b": null}}'::json;
</programlisting>
</programlisting>
</para>
<para>
@ -262,7 +262,7 @@ SELECT '{"reading": 1.230e-5}'::json, '{"reading": 1.230e-5}'::jsonb;
one <type>jsonb</> document has contained within it another one.
These examples return true except as noted:
</para>
<programlisting>
<programlisting>
-- Simple scalar/primitive values contain only the identical value:
SELECT '"foo"'::jsonb @> '"foo"'::jsonb;
@ -282,7 +282,7 @@ SELECT '[1, 2, [1, 3]]'::jsonb @> '[[1, 3]]'::jsonb;
-- Similarly, containment is not reported here:
SELECT '{"foo": {"bar": "baz"}}'::jsonb @> '{"bar": "baz"}'::jsonb; -- yields false
</programlisting>
</programlisting>
<para>
The general principle is that the contained object must match the
@ -296,13 +296,13 @@ SELECT '{"foo": {"bar": "baz"}}'::jsonb @> '{"bar": "baz"}'::jsonb; -- yields f
As a special exception to the general principle that the structures
must match, an array may contain a primitive value:
</para>
<programlisting>
<programlisting>
-- This array contains the primitive string value:
SELECT '["foo", "bar"]'::jsonb @> '"bar"'::jsonb;
-- This exception is not reciprocal -- non-containment is reported here:
SELECT '"bar"'::jsonb @> '["bar"]'::jsonb; -- yields false
</programlisting>
</programlisting>
<para>
<type>jsonb</> also has an <firstterm>existence</> operator, which is
@ -363,22 +363,22 @@ SELECT '"foo"'::jsonb ? 'foo';
(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:
<programlisting>
<programlisting>
CREATE INDEX idxgin ON api USING gin (jdoc);
</programlisting>
</programlisting>
The non-default GIN operator class <literal>jsonb_path_ops</>
supports indexing the <literal>@&gt;</> operator only.
An example of creating an index with this operator class is:
<programlisting>
<programlisting>
CREATE INDEX idxginp ON api USING gin (jdoc jsonb_path_ops);
</programlisting>
</programlisting>
</para>
<para>
Consider the example of a table that stores JSON documents
retrieved from a third-party web service, with a documented schema
definition. A typical document is:
<programlisting>
<programlisting>
{
"guid": "9c36adc1-7fb5-4d5b-83b4-90356a46061a",
"name": "Angela Barton",
@ -394,32 +394,32 @@ CREATE INDEX idxginp ON api USING gin (jdoc jsonb_path_ops);
"qui"
]
}
</programlisting>
</programlisting>
We store these documents in a table named <structname>api</>,
in a <type>jsonb</> column named <structfield>jdoc</>.
If a GIN index is created on this column,
queries like the following can make use of the index:
<programlisting>
<programlisting>
-- Find documents in which the key "company" has value "Magnafone"
SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"company": "Magnafone"}';
</programlisting>
</programlisting>
However, the index could not be used for queries like the
following, because though the operator <literal>?</> is indexable,
it is not applied directly to the indexed column <structfield>jdoc</>:
<programlisting>
<programlisting>
-- Find documents in which the key "tags" contains key or array element "qui"
SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc -&gt; 'tags' ? 'qui';
</programlisting>
</programlisting>
Still, with appropriate use of expression indexes, the above
query can use an index. If querying for particular items within
the <literal>"tags"</> key is common, defining an index like this
may be worthwhile:
<programlisting>
<programlisting>
-- Note that the "jsonb -&gt; text" operator can only be called on a JSON
-- object, so as a consequence of creating this index the root of each
-- "jdoc" value must be an object. This is enforced during insertion.
CREATE INDEX idxgintags ON api USING gin ((jdoc -&gt; 'tags'));
</programlisting>
</programlisting>
Now, the <literal>WHERE</> clause <literal>jdoc -&gt; 'tags' ? 'qui'</>
will be recognized as an application of the indexable
operator <literal>?</> to the indexed
@ -429,10 +429,10 @@ CREATE INDEX idxgintags ON api USING gin ((jdoc -&gt; 'tags'));
</para>
<para>
Another approach to querying is to exploit containment, for example:
<programlisting>
<programlisting>
-- Find documents in which the key "tags" contains array element "qui"
SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qui"]}';
</programlisting>
</programlisting>
A simple GIN index on the <structfield>jdoc</> column can support this
query. But note that such an index will store copies of every key and
value in the <structfield>jdoc</> column, whereas the expression index
@ -460,7 +460,7 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
and a <literal>jsonb_path_ops</literal> GIN index is that the former
creates independent index items for each key and value in the data,
while the latter creates index items only for each value in the
data.
data.
<footnote>
<para>
For this purpose, the term <quote>value</> includes array elements,
@ -501,17 +501,17 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
equality of complete JSON documents.
The <literal>btree</> ordering for <type>jsonb</> datums is seldom
of great interest, but for completeness it is:
<synopsis>
<replaceable>Object</replaceable> > <replaceable>Array</replaceable> > <replaceable>Boolean</replaceable> > <replaceable>Number</replaceable> > <replaceable>String</replaceable> > <replaceable>Null</replaceable>
<synopsis>
<replaceable>Object</replaceable> > <replaceable>Array</replaceable> > <replaceable>Boolean</replaceable> > <replaceable>Number</replaceable> > <replaceable>String</replaceable> > <replaceable>Null</replaceable>
<replaceable>Object with n pairs</replaceable> > <replaceable>object with n - 1 pairs</replaceable>
<replaceable>Object with n pairs</replaceable> > <replaceable>object with n - 1 pairs</replaceable>
<replaceable>Array with n elements</replaceable> > <replaceable>array with n - 1 elements</replaceable>
</synopsis>
<replaceable>Array with n elements</replaceable> > <replaceable>array with n - 1 elements</replaceable>
</synopsis>
Objects with equal numbers of pairs are compared in the order:
<synopsis>
<replaceable>key-1</replaceable>, <replaceable>value-1</replaceable>, <replaceable>key-2</replaceable> ...
</synopsis>
<synopsis>
<replaceable>key-1</replaceable>, <replaceable>value-1</replaceable>, <replaceable>key-2</replaceable> ...
</synopsis>
Note that object keys are compared in their storage order;
in particular, since shorter keys are stored before longer keys, this
can lead to results that might be unintuitive, such as:
@ -520,9 +520,9 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
</programlisting>
Similarly, arrays with equal numbers of elements are compared in the
order:
<synopsis>
<replaceable>element-1</replaceable>, <replaceable>element-2</replaceable> ...
</synopsis>
<synopsis>
<replaceable>element-1</replaceable>, <replaceable>element-2</replaceable> ...
</synopsis>
Primitive JSON values are compared using the same
comparison rules as for the underlying
<productname>PostgreSQL</productname> data type. Strings are