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doc: adjust JSONB GIN index description 

Backpatch through 9.4
This commit is contained in:
Bruce Momjian 2014-06-21 15:33:23 -04:00
parent a52f2a0b9c
commit 884dede37a
1 changed files with 10 additions and 5 deletions
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15
doc/src/sgml/json.sgml
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@ -460,11 +460,16 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @> '{"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.<footnote><para>For this purpose, the term <quote>value</>
includes array elements, though JSON terminology sometimes considers
array elements distinct from values within objects.</para></footnote>
But in <literal>jsonb_path_ops</literal>, each index item is a hash
of both the value and the key(s) leading to it; for example to index
data.
<footnote>
<para>
For this purpose, the term <quote>value</> includes array elements,
though JSON terminology sometimes considers array elements distinct
from values within objects.
</para>
</footnote>
Basically, each <literal>jsonb_path_ops</literal> index item is
a hash of the value and the key(s) leading to it; for example to index
<literal>{"foo": {"bar": "baz"}}</literal>, a single index item would
be created incorporating all three of <literal>foo</>, <literal>bar</>,
and <literal>baz</> into the hash value. Thus a containment query