Table 9.40, “json and jsonb Operators” shows the operators that are available for use with the two JSON data types (see the section called “JSON Types”).
Table 9.40. json and jsonb Operators
Operator | Right Operand Type | Description | Example | Example Result |
---|---|---|---|---|
-> | int | Get JSON array element (indexed from zero) | '[{"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 standard comparison operators shown in Table 9.1, “Comparison Operators” are available for jsonb, but not for json. They follow the ordering rules for B-tree operations outlined at the section called “jsonb Indexing”.
Some further operators also exist only for jsonb, as shown in Table 9.41, “Additional jsonb Operators”. Many of these operators can be indexed by jsonb operator classes. For a full description of jsonb containment and existence semantics, see the section called “jsonb Containment and Existence”. the section called “jsonb Indexing” describes how these operators can be used to effectively index jsonb data.
Table 9.41. Additional jsonb Operators
Operator | Right Operand Type | Description | Example |
---|---|---|---|
@> | jsonb | Does the left JSON value contain within it the right value? | '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb |
<@ | jsonb | Is the left JSON value contained within the right value? | '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb |
? | text | Does the key/element string exist within the JSON value? | '{"a":1, "b":2}'::jsonb ? 'b' |
?| | text[] | Do any of these key/element strings exist? | '{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c'] |
?& | text[] | Do all of these key/element strings exist? | '["a", "b"]'::jsonb ?& array['a', 'b'] |
Table 9.42, “JSON Creation Functions” shows the functions that are available for creating json values. (Currently, there are no equivalent functions for jsonb, but you can cast the result of one of these functions to jsonb.)
Table 9.42. JSON Creation Functions
Function | Description | Example | Example Result |
---|---|---|---|
to_json(anyelement)
| Returns the value as JSON. 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 JSON scalar value is produced. For any scalar type other than a number, a Boolean, or a null value, the text representation will be used, properly quoted and escaped so that it is a valid JSON string. | 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"} |
json_build_array(VARIADIC "any")
| 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] |
json_build_object(VARIADIC "any")
| 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} |
json_object(text[])
| 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"} |
json_object(keys text[], values text[])
| 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 9.43, “JSON Processing Functions” shows the functions that are available for processing json and jsonb values.
Table 9.43. 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 |
| json jsonb | 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 ---+--- 1 | 2 |
| 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 |
| setof json setof jsonb | 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":"bar"}') as x(a int, b text, d text) | a | b | d ---+---------+--- 1 | [1,2,3] | |
| 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 | |
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 the section called “JSON Types”.
In json_populate_record
, json_populate_recordset
,
json_to_record
and json_to_recordset
,
type coercion from the JSON is “best effort” and may not result
in desired values for some types. JSON keys are matched to
identical column names in the target row type. JSON fields that do not
appear in the target row type will be omitted from the output, and
target columns that do not match any JSON field will simply be NULL.
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.
See also the section called “Aggregate Functions” 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.