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Doc: improve documentation for jsonpath behavior.

Clarify the behavior of jsonpath operators and functions by
describing their two different modes of operation explicitly.
In addition to the SQL-spec behavior, where a path returns
a list of matching items, we have a "predicate check" form
that always returns a single boolean result.  That was mentioned
in only one place, but it seems better to annotate each operator
and function as to which form(s) it takes.  Also improve the
examples by converting them into actual executable SQL with
results, and do a bunch of incidental wordsmithing.

David Wheeler, reviewed by Erik Wienhold, Jian He, and myself

Discussion: https://postgr.es/m/7262A188-59CA-4A8A-AAD7-83D4FF0B9758@justatheory.com
This commit is contained in:
Tom Lane
2024-01-25 11:32:18 -05:00
parent 66ea94e8e6
commit 7014c9a4bb
2 changed files with 271 additions and 120 deletions

View File

@@ -513,7 +513,7 @@ 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
== <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>,