9.15. JSON Functions and Operators
Table 9.42 shows the operators that are available for use with the two JSON data types (seeSection 8.14).
Table 9.42. json andjsonb 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 astext | '[1,2,3]'::json->>2 | 3 |
->> | text | Get JSON object field astext | '{"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 astext | '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' | 3 |
Note
There are parallel variants of these operators for both thejson andjsonb types. The field/element/path extraction operators return the same type as their left-hand input (eitherjson orjsonb), except for those specified as returningtext, 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 inTable 9.1 are available forjsonb, but not forjson. They follow the ordering rules for B-tree operations outlined atSection 8.14.4.
Some further operators also exist only forjsonb, as shown inTable 9.43. Many of these operators can be indexed byjsonb operator classes. For a full description ofjsonb containment and existence semantics, seeSection 8.14.3.Section 8.14.4 describes how these operators can be used to effectively indexjsonb data.
Table 9.43. Additionaljsonb 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 thestring exist as a top-level key within the JSON value? | '{"a":1, "b":2}'::jsonb ? 'b' |
?| | text[] | Do any of these arraystrings exist as top-level keys? | '{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c'] |
?& | text[] | Do all of these arraystrings exist as top-level keys? | '["a", "b"]'::jsonb ?& array['a', 'b'] |
|| | jsonb | Concatenate twojsonb values into a newjsonb value | '["a", "b"]'::jsonb || '["c", "d"]'::jsonb |
- | text | Delete key/value pair orstring element from left operand. Key/value pairs are matched based on their key value. | '{"a": "b"}'::jsonb - 'a' |
- | 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}' |
Note
The|| operator concatenates two JSON objects by generating an object containing the union of their keys, taking the second object's value when there are duplicate keys. All other cases produce a JSON array: first, any non-array input is converted into a single-element array, and then the two arrays are concatenated. It does not operate recursively; only the top-level array or object structure is merged.
Table 9.44 shows the functions that are available for creatingjson andjsonb values. (There are no equivalent functions forjsonb, of therow_to_json andarray_to_json functions. However, theto_jsonb function supplies much the same functionality as these functions would.)
Table 9.44. JSON Creation Functions
| Function | Description | Example | Example Result |
|---|---|---|---|
| Returns the value asjson orjsonb. Arrays and composites are converted (recursively) to arrays and objects; otherwise, if there is a cast from the type tojson, 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 validjson orjsonb 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 ifpretty_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 ifpretty_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 ofjson_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"} |
Note
array_to_json androw_to_json have the same behavior asto_json except for offering a pretty-printing option. The behavior described forto_json likewise applies to each individual value converted by the other JSON creation functions.
Note
Thehstore extension has a cast fromhstore tojson, so thathstore values converted via the JSON creation functions will be represented as JSON objects, not as primitive string values.
Table 9.45 shows the functions that are available for processingjson andjsonb values.
Table 9.45. 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 typetext. | select * from json_each_text('{"a":"foo", "b":"bar"}') | key | value-----+------- a | foo b | bar |
|
| Returns JSON value pointed to bypath_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 bypath_elems astext (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 infrom_json to a row whose columns match the record type defined bybase (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 infrom_json to a set of rows whose columns match the record type defined bybase (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 oftext 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 areobject,array,string,number,boolean, andnull. | json_typeof('-123.4') | number |
| record | Builds an arbitrary record from a JSON object (see note below). As with all functions returningrecord, the caller must explicitly define the structure of the record with anAS 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 returningrecord, the caller must explicitly define the structure of the record with anAS 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 | |
|
| Returnsfrom_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] |
|
| Returnstarget with the section designated bypath replaced bynew_value, or withnew_value added ifcreate_missing is true (default istrue) and the item designated bypath does not exist. As with the path oriented operators, negative integers that appear inpath count from the end of JSON arrays. |
|
|
|
| Returnstarget withnew_value inserted. Iftarget section designated bypath is in a JSONB array,new_value will be inserted before target or after ifinsert_after is true (default isfalse). Iftarget section designated bypath is in JSONB object,new_value will be inserted only iftarget does not exist. As with the path oriented operators, negative integers that appear inpath count from the end of JSON arrays. |
|
|
|
| Returnsfrom_json as indented JSON text. | jsonb_pretty('[{"f1":1,"f2":null},2,null,3]') | [ { "f1": 1, "f2": null }, 2, null, 3] |
Note
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 typejsonb, because the conversion was already done; but forjson input, this may result in throwing an error, as noted inSection 8.14.
Note
While the examples for the functionsjson_populate_record,json_populate_recordset,json_to_record andjson_to_recordset use constants, the typical use would be to reference a table in theFROM clause and use one of itsjson orjsonb columns as an argument to the function. Extracted key values can then be referenced in other parts of the query, likeWHERE clauses and target lists. Extracting multiple values in this way can improve performance over extracting them separately with per-key operators.
JSON keys are matched to identical column names in the target row type. JSON type coercion for these functions is“best effort” and may not result in desired values for some types. 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.
Note
All the items of thepath parameter ofjsonb_set as well asjsonb_insert except the last item must be present in thetarget. Ifcreate_missing is false, all items of thepath parameter ofjsonb_set must be present. If these conditions are not met thetarget 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.
Note
Thejson_typeof function'snull return value should not be confused with a SQL NULL. While callingjson_typeof('null'::json) will returnnull, callingjson_typeof(NULL::json) will return a SQL NULL.
Note
If the argument tojson_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 forjsonb_strip_nulls sincejsonb values never have duplicate object field names.
See alsoSection 9.20 for the aggregate functionjson_agg which aggregates record values as JSON, and the aggregate functionjson_object_agg which aggregates pairs of values into a JSON object, and theirjsonb equivalents,jsonb_agg andjsonb_object_agg.