Table 9.43 shows the operators that are available for use with the two JSON data types (see Section 8.14).
Table 9.43. json and jsonb Operators
| Operator | Right Operand Type | Description | Example | Example Result |
|---|---|---|---|---|
-> | int | Get JSON array element (indexed from zero, negative integers count from the end) | '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 | {"c":"baz"} |
-> | text | Get JSON object field by key | '{"a": {"b":"foo"}}'::json->'a' | {"b":"foo"} |
->> | int | Get JSON array element as text | '[1,2,3]'::json->>2 | 3 |
->> | text | Get JSON object field as text | '{"a":1,"b":2}'::json->>'b' | 2 |
#> | text[] | Get JSON object at specified path | '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}' | {"c": "foo"} |
#>> | text[] | Get JSON object at specified path as text | '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' | 3 |
There are parallel variants of these operators for both the
json and jsonb types.
The field/element/path extraction operators
return the same type as their left-hand input (either json
or jsonb), except for those specified as
returning text, which coerce the value to text.
The field/element/path extraction operators return NULL, rather than
failing, if the JSON input does not have the right structure to match
the request; for example if no such element exists. The
field/element/path extraction operators that accept integer JSON
array subscripts all support negative subscripting from the end of
arrays.
The standard comparison operators shown in Table 9.1 are available for
jsonb, but not for json. They follow the
ordering rules for B-tree operations outlined at Section 8.14.4.
Some further operators also exist only for jsonb, as shown
in Table 9.44.
Many of these operators can be indexed by
jsonb operator classes. For a full description of
jsonb containment and existence semantics, see Section 8.14.3. Section 8.14.4
describes how these operators can be used to effectively index
jsonb data.
Table 9.44. Additional jsonb Operators
| Operator | Right Operand Type | Description | Example |
|---|---|---|---|
@> | jsonb | Does the left JSON value contain the right JSON path/value entries at the top level? | '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb |
<@ | jsonb | Are the left JSON path/value entries contained at the top level within the right JSON value? | '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb |
? | text | Does the string exist as a top-level key within the JSON value? | '{"a":1, "b":2}'::jsonb ? 'b' |
?| | text[] | Do any of these array strings exist as top-level keys? | '{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c'] |
?& | text[] | Do all of these array strings exist as top-level keys? | '["a", "b"]'::jsonb ?& array['a', 'b'] |
|| | jsonb | Concatenate two jsonb values into a new jsonb value | '["a", "b"]'::jsonb || '["c", "d"]'::jsonb |
- | text | Delete key/value pair or string element from left operand. Key/value pairs are matched based on their key value. | '{"a": "b"}'::jsonb - 'a' |
- | text[] | Delete multiple key/value pairs or string elements from left operand. Key/value pairs are matched based on their key value. | '{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[] |
- | integer | Delete the array element with specified index (Negative integers count from the end). Throws an error if top level container is not an array. | '["a", "b"]'::jsonb - 1 |
#- | text[] | Delete the field or element with specified path (for JSON arrays, negative integers count from the end) | '["a", {"b":1}]'::jsonb #- '{1,b}' |
The || operator concatenates the elements at the top level of
each of its operands. It does not operate recursively. For example, if
both operands are objects with a common key field name, the value of the
field in the result will just be the value from the right hand operand.
Table 9.45 shows the functions that are
available for creating json and jsonb values.
(There are no equivalent functions for jsonb, of the row_to_json
and array_to_json functions. However, the to_jsonb
function supplies much the same functionality as these functions would.)
Table 9.45. JSON Creation Functions
| Function | Description | Example | Example Result |
|---|---|---|---|
|
Returns the value as json or jsonb.
Arrays and composites are converted
(recursively) to arrays and objects; otherwise, if there is a cast
from the type to json, the cast function will be used to
perform the conversion; otherwise, a scalar value is produced.
For any scalar type other than a number, a Boolean, or a null value,
the text representation will be used, in such a fashion that it is a
valid json or jsonb value.
| to_json('Fred said "Hi."'::text) | "Fred said \"Hi.\"" |
array_to_json(anyarray [, pretty_bool])
|
Returns the array as a JSON array. A PostgreSQL multidimensional array
becomes a JSON array of arrays. Line feeds will be added between
dimension-1 elements if pretty_bool is true.
| array_to_json('{{1,5},{99,100}}'::int[]) | [[1,5],[99,100]] |
row_to_json(record [, pretty_bool])
|
Returns the row as a JSON object. Line feeds will be added between
level-1 elements if pretty_bool is true.
| row_to_json(row(1,'foo')) | {"f1":1,"f2":"foo"} |
| Builds a possibly-heterogeneously-typed JSON array out of a variadic argument list. | json_build_array(1,2,'3',4,5) | [1, 2, "3", 4, 5] |
| Builds a JSON object out of a variadic argument list. By convention, the argument list consists of alternating keys and values. | json_build_object('foo',1,'bar',2) | {"foo": 1, "bar": 2} |
| Builds a JSON object out of a text array. The array must have either exactly one dimension with an even number of members, in which case they are taken as alternating key/value pairs, or two dimensions such that each inner array has exactly two elements, which are taken as a key/value pair. |
| {"a": "1", "b": "def", "c": "3.5"} |
|
This form of json_object takes keys and values pairwise from two separate
arrays. In all other respects it is identical to the one-argument form.
| json_object('{a, b}', '{1,2}') | {"a": "1", "b": "2"} |
array_to_json and row_to_json have the same
behavior as to_json except for offering a pretty-printing
option. The behavior described for to_json likewise applies
to each individual value converted by the other JSON creation functions.
The hstore extension has a cast
from hstore to json, so that
hstore values converted via the JSON creation functions
will be represented as JSON objects, not as primitive string values.
Table 9.46 shows the functions that
are available for processing json and jsonb values.
Table 9.46. JSON Processing Functions
| Function | Return Type | Description | Example | Example Result |
|---|---|---|---|---|
| int | Returns the number of elements in the outermost JSON array. | json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]') | 5 |
|
| Expands the outermost JSON object into a set of key/value pairs. | select * from json_each('{"a":"foo", "b":"bar"}') |
key | value -----+------- a | "foo" b | "bar" |
| setof key text, value text |
Expands the outermost JSON object into a set of key/value pairs. The
returned values will be of type text.
| select * from json_each_text('{"a":"foo", "b":"bar"}') |
key | value -----+------- a | foo b | bar |
|
|
Returns JSON value pointed to by path_elems
(equivalent to #> operator).
| json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4') | {"f5":99,"f6":"foo"} |
| text |
Returns JSON value pointed to by path_elems
as text
(equivalent to #>> operator).
| json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6') | foo |
| setof text | Returns set of keys in the outermost JSON object. | json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}') |
json_object_keys ------------------ f1 f2 |
| anyelement |
Expands the object in from_json to a row
whose columns match the record type defined by base
(see note below).
| select * from json_populate_record(null::myrowtype, '{"a": 1, "b": ["2", "a b"], "c": {"d": 4, "e": "a b c"}}') |
a | b | c
---+-----------+-------------
1 | {2,"a b"} | (4,"a b c")
|
| setof anyelement |
Expands the outermost array of objects
in from_json to a set of rows whose
columns match the record type defined by base (see
note below).
| select * from json_populate_recordset(null::myrowtype, '[{"a":1,"b":2},{"a":3,"b":4}]') |
a | b ---+--- 1 | 2 3 | 4 |
|
| Expands a JSON array to a set of JSON values. | select * from json_array_elements('[1,true, [2,false]]') |
value ----------- 1 true [2,false] |
| setof text |
Expands a JSON array to a set of text values.
| select * from json_array_elements_text('["foo", "bar"]') |
value ----------- foo bar |
| text |
Returns the type of the outermost JSON value as a text string.
Possible types are
object, array, string, number,
boolean, and null.
| json_typeof('-123.4') | number |
| record |
Builds an arbitrary record from a JSON object (see note below). As
with all functions returning record, the caller must
explicitly define the structure of the record with an AS
clause.
| select * from json_to_record('{"a":1,"b":[1,2,3],"c":[1,2,3],"e":"bar","r": {"a": 123, "b": "a b c"}}') as x(a int, b text, c int[], d text, r myrowtype) |
a | b | c | d | r
---+---------+---------+---+---------------
1 | [1,2,3] | {1,2,3} | | (123,"a b c")
|
| setof record |
Builds an arbitrary set of records from a JSON array of objects (see
note below). As with all functions returning record, the
caller must explicitly define the structure of the record with
an AS clause.
| select * from json_to_recordset('[{"a":1,"b":"foo"},{"a":"2","c":"bar"}]') as x(a int, b text); |
a | b ---+----- 1 | foo 2 | |
|
|
Returns from_json
with all object fields that have null values omitted. Other null values
are untouched.
| json_strip_nulls('[{"f1":1,"f2":null},2,null,3]') | [{"f1":1},2,null,3] |
|
|
Returns target
with the section designated by path
replaced by new_value, or with
new_value added if
create_missing is true ( default is
true) and the item
designated by path does not exist.
As with the path orientated operators, negative integers that
appear in path count from the end
of JSON arrays.
|
|
|
|
|
|
Returns target with
new_value inserted. If
target section designated by
path is in a JSONB array,
new_value will be inserted before target or
after if insert_after is true (default is
false). If target section
designated by path is in JSONB object,
new_value will be inserted only if
target does not exist. As with the path
orientated operators, negative integers that appear in
path count from the end of JSON arrays.
|
|
|
|
|
Returns from_json
as indented JSON text.
| jsonb_pretty('[{"f1":1,"f2":null},2,null,3]') |
[
{
"f1": 1,
"f2": null
},
2,
null,
3
]
|
Many of these functions and operators will convert Unicode escapes in
JSON strings to the appropriate single character. This is a non-issue
if the input is type jsonb, because the conversion was already
done; but for json input, this may result in throwing an error,
as noted in Section 8.14.
The functions
json[b]_populate_record,
json[b]_populate_recordset,
json[b]_to_record and
json[b]_to_recordset
operate on a JSON object, or array of objects, and extract the values
associated with keys whose names match column names of the output row
type.
Object fields that do not correspond to any output column name are
ignored, and output columns that do not match any object field will be
filled with nulls.
To convert a JSON value to the SQL type of an output column, the
following rules are applied in sequence:
A JSON null value is converted to a SQL null in all cases.
If the output column is of type json
or jsonb, the JSON value is just reproduced exactly.
If the output column is a composite (row) type, and the JSON value is a JSON object, the fields of the object are converted to columns of the output row type by recursive application of these rules.
Likewise, if the output column is an array type and the JSON value is a JSON array, the elements of the JSON array are converted to elements of the output array by recursive application of these rules.
Otherwise, if the JSON value is a string literal, the contents of the string are fed to the input conversion function for the column's data type.
Otherwise, the ordinary text representation of the JSON value is fed to the input conversion function for the column's data type.
While the examples for these functions use constants, the typical use
would be to reference a table in the FROM clause
and use one of its json or jsonb columns
as an argument to the function. Extracted key values can then be
referenced in other parts of the query, like WHERE
clauses and target lists. Extracting multiple values in this
way can improve performance over extracting them separately with
per-key operators.
All the items of the path parameter of jsonb_set
as well as jsonb_insert except the last item must be present
in the target. If create_missing is false, all
items of the path parameter of jsonb_set must be
present. If these conditions are not met the target is
returned unchanged.
If the last path item is an object key, it will be created if it
is absent and given the new value. If the last path item is an array
index, if it is positive the item to set is found by counting from
the left, and if negative by counting from the right - -1
designates the rightmost element, and so on.
If the item is out of the range -array_length .. array_length -1,
and create_missing is true, the new value is added at the beginning
of the array if the item is negative, and at the end of the array if
it is positive.
The json_typeof function's null return value
should not be confused with a SQL NULL. While
calling json_typeof('null'::json) will
return null, calling json_typeof(NULL::json)
will return a SQL NULL.
If the argument to json_strip_nulls contains duplicate
field names in any object, the result could be semantically somewhat
different, depending on the order in which they occur. This is not an
issue for jsonb_strip_nulls since jsonb values never have
duplicate object field names.
See also Section 9.20 for the aggregate
function json_agg which aggregates record
values as JSON, and the aggregate function
json_object_agg which aggregates pairs of values
into a JSON object, and their jsonb equivalents,
jsonb_agg and jsonb_object_agg.