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Improve documentation for array subscription in jsonpath

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Usage of expressions and multiple ranges in jsonpath array subscription was
undocumented.  This commit adds lacking documentation.
This commit is contained in:
Alexander Korotkov 2019-05-17 05:47:53 +03:00
parent e0e3dad770
commit 87bcc02f4f
1 changed files with 13 additions and 8 deletions
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21
doc/src/sgml/json.sgml
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@ -836,17 +836,22 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @> '{"tags": ["qu
<para>
<literal>[<replaceable>subscript</replaceable>, ...]</literal>
</para>
<para>
<literal>[<replaceable>subscript</replaceable> to last]</literal>
</para>
</entry>
<entry>
<para>
Array element accessor. The provided numeric subscripts return the
corresponding array elements. The first element in an array is
accessed with [0]. The <literal>last</literal> keyword denotes
the last subscript in an array and can be used to handle arrays
of unknown length.
Array element accessor. <literal><replaceable>subscript</replaceable></literal>
might be given in two forms: <literal><replaceable>expr</replaceable></literal>
or <literal><replaceable>lower_expr</replaceable> to <replaceable>upper_expr</replaceable></literal>.
The first form specifies single array element by its index. The second
form specified array slice by the range of indexes. Zero index
corresponds to the first array element.
</para>
<para>
Expression inside subscript may consititue an integer,
numeric expression or any other <literal>jsonpath</literal> expression
returning single numeric value. The <literal>last</literal> keyword
can be used in the expression denoting the last subscript in an array.
That's helpful for handling arrays of unknown length.
</para>
</entry>
</row>