Supported Versions: Current (11) / 10 / 9.6 / 9.5 / 9.4
Development Versions: 12 / devel
Unsupported versions: 9.3 / 9.2

9.15. JSON Functions, Operators, and Expressions

The functions, operators, and expressions described in this section operate on JSON data:

To learn more about the SQL/JSON standard, see [sqltr-19075-6]. For details on JSON types supported in PostgreSQL, see Section 8.14.

9.15.1. SQL/JSON Path Expressions

SQL/JSON path expressions specify the items to be retrieved from the JSON data, similar to XPath expressions used for SQL access to XML. In PostgreSQL, path expressions are implemented as the jsonpath data type, described in Section 8.14.6.

JSON query functions and operators pass the provided path expression to the path engine for evaluation. If the expression matches the JSON data to be queried, the corresponding SQL/JSON item is returned. Path expressions are written in the SQL/JSON path language and can also include arithmetic expressions and functions. Query functions treat the provided expression as a text string, so it must be enclosed in single quotes.

A path expression consists of a sequence of elements allowed by the jsonpath data type. The path expression is evaluated from left to right, but you can use parentheses to change the order of operations. If the evaluation is successful, a sequence of SQL/JSON items (SQL/JSON sequence) is produced, and the evaluation result is returned to the JSON query function that completes the specified computation.

To refer to the JSON data to be queried (the context item), use the $ sign in the path expression. It can be followed by one or more accessor operators, which go down the JSON structure level by level to retrieve the content of context item. Each operator that follows deals with the result of the previous evaluation step.

For example, suppose you have some JSON data from a GPS tracker that you would like to parse, such as:

{ "track" :
  {
    "segments" : [ 
      { "location":   [ 47.763, 13.4034 ],
        "start time": "2018-10-14 10:05:14",
        "HR": 73
      },
      { "location":   [ 47.706, 13.2635 ],
        "start time": "2018-10-14 10:39:21",
        "HR": 130
      } ]
  }
}

To retrieve the available track segments, you need to use the .key accessor operator for all the preceding JSON objects:

'$.track.segments'

If the item to retrieve is an element of an array, you have to unnest this array using the [*] operator. For example, the following path will return location coordinates for all the available track segments:

'$.track.segments[*].location'

To return the coordinates of the first segment only, you can specify the corresponding subscript in the [] accessor operator. Note that the SQL/JSON arrays are 0-relative:

'$.track.segments[0].location'

The result of each path evaluation step can be processed by one or more jsonpath operators and methods listed in Section 9.15.1.2. Each method must be preceded by a dot, while arithmetic and boolean operators are separated from the operands by spaces. For example, you can get an array size:

'$.track.segments.size()'

For more examples of using jsonpath operators and methods within path expressions, see Section 9.15.1.2.

When defining the path, you can also use one or more filter expressions, which work similar to the WHERE clause in SQL. Each filter expression can provide one or more filtering conditions that are applied to the result of the path evaluation. Each filter expression must be enclosed in parentheses and preceded by a question mark. Filter expressions are evaluated from left to right and can be nested. The @ variable denotes the current path evaluation result to be filtered, and can be followed by one or more accessor operators to define the JSON element by which to filter the result. Functions and operators that can be used in the filtering condition are listed in Table 9.45. SQL/JSON defines three-valued logic, so the result of the filter expression may be true, false, or unknown. The unknown value plays the same role as SQL NULL. Further path evaluation steps use only those items for which filter expressions return true.

Suppose you would like to retrieve all heart rate values higher than 130. You can achieve this using the following expression:

'$.track.segments[*].HR ? (@ > 130)'

To get the start time of segments with such values instead, you have to filter out irrelevant segments before returning the start time, so the filter is applied to the previous step and the path in the filtering condition is different:

'$.track.segments[*] ? (@.HR > 130)."start time"'

You can use several filter expressions on the same nesting level, if required. For example, the following expression selects all segments that contain locations with relevant coordinates and high heart rate values:

'$.track.segments[*] ? (@.location[1] < 13.4) ? (@.HR > 130)."start time"'

Using filter expressions at different nesting levels is also allowed. The following example first filters all segments by location, and then returns high heart rate values for these segments, if available:

'$.track.segments[*] ? (@.location[1] < 13.4).HR ? (@ > 130)'

You can also nest filters within each other:

'$.track ? (@.segments[*] ? (@.HR > 130)).segments.size()'

This expression returns the size of the track if it contains any segments with high heart rate values, or an empty sequence otherwise.

PostgreSQL's implementation of SQL/JSON path language has the following deviations from the SQL/JSON standard:

  • .datetime() item method is not implemented yet mainly because immutable jsonpath functions and operators cannot reference session timezone, which is used in some datetime operations. Datetime support will be added to jsonpath in future versions of PostgreSQL.

  • A path expression can be a boolean predicate, although the SQL/JSON standard allows predicates only in filters. This is necessary for implementation of the @@ operator. For example, the followingjsonpath expression is valid in PostgreSQL:

    '$.track.segments[*].HR < 70'
    

9.15.1.1. Strict and Lax Modes

When you query JSON data, the path expression may not match the actual JSON data structure. An attempt to access a non-existent member of an object or element of an array results in a structural error. SQL/JSON path expressions have two modes of handling structural errors:

  • lax (default) — the path engine implicitly adapts the queried data to the specified path. Any remaining structural errors are suppressed and converted to empty SQL/JSON sequences.

  • strict — if a structural error occurs, an error is raised.

The lax mode facilitates matching of a JSON document structure and path expression if the JSON data does not conform to the expected schema. If an operand does not match the requirements of a particular operation, it can be automatically wrapped as an SQL/JSON array or unwrapped by converting its elements into an SQL/JSON sequence before performing this operation. Besides, comparison operators automatically unwrap their operands in the lax mode, so you can compare SQL/JSON arrays out-of-the-box. An array of size 1 is considered equal to its sole element. Automatic unwrapping is not performed only when:

  • The path expression contains type() or size() methods that return the type and the number of elements in the array, respectively.

  • The queried JSON data contain nested arrays. In this case, only the outermost array is unwrapped, while all the inner arrays remain unchanged. Thus, implicit unwrapping can only go one level down within each path evaluation step.

For example, when querying the GPS data listed above, you can abstract from the fact that it stores an array of segments when using the lax mode:

'lax $.track.segments.location'

In the strict mode, the specified path must exactly match the structure of the queried JSON document to return an SQL/JSON item, so using this path expression will cause an error. To get the same result as in the lax mode, you have to explicitly unwrap the segments array:

'strict $.track.segments[*].location'

9.15.1.2. SQL/JSON Path Operators and Methods

Table 9.44. jsonpath Operators and Methods

Operator/Method Description Example JSON Example Query Result
+ (unary) Plus operator that iterates over the SQL/JSON sequence {"x": [2.85, -14.7, -9.4]} + $.x.floor() 2, -15, -10
- (unary) Minus operator that iterates over the SQL/JSON sequence {"x": [2.85, -14.7, -9.4]} - $.x.floor() -2, 15, 10
+ (binary) Addition [2] 2 + $[0] 4
- (binary) Subtraction [2] 4 - $[0] 2
* Multiplication [4] 2 * $[0] 8
/ Division [8] $[0] / 2 4
% Modulus [32] $[0] % 10 2
type() Type of the SQL/JSON item [1, "2", {}] $[*].type() "number", "string", "object"
size() Size of the SQL/JSON item {"m": [11, 15]} $.m.size() 2
double() Approximate numeric value converted from a string {"len": "1.9"} $.len.double() * 2 3.8
ceiling() Nearest integer greater than or equal to the SQL/JSON number {"h": 1.3} $.h.ceiling() 2
floor() Nearest integer less than or equal to the SQL/JSON number {"h": 1.3} $.h.floor() 1
abs() Absolute value of the SQL/JSON number {"z": -0.3} $.z.abs() 0.3
keyvalue() Sequence of object's key-value pairs represented as array of objects containing three fields ("key", "value", and "id"). "id" is an unique identifier of the object key-value pair belongs to. {"x": "20", "y": 32} $.keyvalue() {"key": "x", "value": "20", "id": 0}, {"key": "y", "value": 32, "id": 0}

Table 9.45. jsonpath Filter Expression Elements

Value/Predicate Description Example JSON Example Query Result
== Equality operator [1, 2, 1, 3] $[*] ? (@ == 1) 1, 1
!= Non-equality operator [1, 2, 1, 3] $[*] ? (@ != 1) 2, 3
<> Non-equality operator (same as !=) [1, 2, 1, 3] $[*] ? (@ <> 1) 2, 3
< Less-than operator [1, 2, 3] $[*] ? (@ < 2) 1, 2
<= Less-than-or-equal-to operator [1, 2, 3] $[*] ? (@ < 2) 1
> Greater-than operator [1, 2, 3] $[*] ? (@ > 2) 3
> Greater-than-or-equal-to operator [1, 2, 3] $[*] ? (@ >= 2) 2, 3
true Value used to perform comparison with JSON true literal [{"name": "John", "parent": false}, {"name": "Chris", "parent": true}] $[*] ? (@.parent == true) {"name": "Chris", "parent": true}
false Value used to perform comparison with JSON false literal [{"name": "John", "parent": false}, {"name": "Chris", "parent": true}] $[*] ? (@.parent == false) {"name": "John", "parent": false}
null Value used to perform comparison with JSON null value [{"name": "Mary", "job": null}, {"name": "Michael", "job": "driver"}] $[*] ? (@.job == null) .name "Mary"
&& Boolean AND [1, 3, 7] $[*] ? (@ > 1 && @ < 5) 3
|| Boolean OR [1, 3, 7] $[*] ? (@ < 1 || @ > 5) 7
! Boolean NOT [1, 3, 7] $[*] ? (!(@ < 5)) 7
like_regex Tests pattern matching with POSIX regular expressions ["abc", "abd", "aBdC", "abdacb", "babc"] $[*] ? (@ like_regex "^ab.*c" flag "i") "abc", "aBdC", "abdacb"
starts with Tests whether the second operand is an initial substring of the first operand ["John Smith", "Mary Stone", "Bob Johnson"] $[*] ? (@ starts with "John") "John Smith"
exists Tests whether a path expression has at least one SQL/JSON item {"x": [1, 2], "y": [2, 4]} strict $.* ? (exists (@ ? (@[*] > 2))) 2, 4
is unknown Tests whether a boolean condition is unknown [-1, 2, 7, "infinity"] $[*] ? ((@ > 0) is unknown) "infinity"

9.15.2. JSON Functions and Operators

Table 9.46 shows the operators that are available for use with JSON data types (see Section 8.14).

Table 9.46. json and jsonb Operators

Operator Right Operand Type Return type Description Example Example Result
-> int json or jsonb Get JSON array element (indexed from zero, negative integers count from the end) '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 {"c":"baz"}
-> text json or jsonb Get JSON object field by key '{"a": {"b":"foo"}}'::json->'a' {"b":"foo"}
->> int text Get JSON array element as text '[1,2,3]'::json->>2 3
->> text text Get JSON object field as text '{"a":1,"b":2}'::json->>'b' 2
#> text[] json or jsonb Get JSON object at the specified path '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}' {"c": "foo"}
#>> text[] text Get JSON object at the specified path as text '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' 3

Note

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 9.47. 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 9.47. 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}'
@? jsonpath Does JSON path returns any item for the specified JSON value? '{"a":[1,2,3,4,5]}'::jsonb @? '$.a[*] ? (@ > 2)'
@@ jsonpath JSON path predicate check result for the specified JSON value. Only first result item is taken into account. If there is no results or first result item is not bool, then NULL is returned. '{"a":[1,2,3,4,5]}'::jsonb @@ '$.a[*] > 2'

Note

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.

Note

The @? and @@ operators suppress errors including: lacking object field or array element, unexpected JSON item type and numeric errors. This behavior might be helpful while searching over JSON document collections of varying structure.

Table 9.48 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 9.48. JSON Creation Functions

Function Description Example Example Result

to_json(anyelement)

to_jsonb(anyelement)

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"}

json_build_array(VARIADIC "any")

jsonb_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")

jsonb_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[])

jsonb_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.

json_object('{a, 1, b, "def", c, 3.5}')

json_object('{{a, 1},{b, "def"},{c, 3.5}}')

{"a": "1", "b": "def", "c": "3.5"}

json_object(keys text[], values text[])

jsonb_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"}

Note

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.

Note

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 9.49 shows the functions that are available for processing json and jsonb values.

Table 9.49. JSON Processing Functions

Function Return Type Description Example Example Result

json_array_length(json)

jsonb_array_length(jsonb)

int Returns the number of elements in the outermost JSON array. json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]') 5

json_each(json)

jsonb_each(jsonb)

setof key text, value json

setof key text, value jsonb

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"

json_each_text(json)

jsonb_each_text(jsonb)

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_extract_path(from_json json, VARIADIC path_elems text[])

jsonb_extract_path(from_json jsonb, VARIADIC path_elems text[])

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"}

json_extract_path_text(from_json json, VARIADIC path_elems text[])

jsonb_extract_path_text(from_json jsonb, VARIADIC path_elems text[])

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

json_object_keys(json)

jsonb_object_keys(jsonb)

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

json_populate_record(base anyelement, from_json json)

jsonb_populate_record(base anyelement, from_json jsonb)

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")

json_populate_recordset(base anyelement, from_json json)

jsonb_populate_recordset(base anyelement, from_json jsonb)

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

json_array_elements(json)

jsonb_array_elements(jsonb)

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]

json_array_elements_text(json)

jsonb_array_elements_text(jsonb)

setof text Expands a JSON array to a set of text values. select * from json_array_elements_text('["foo", "bar"]')
   value
-----------
 foo
 bar

json_typeof(json)

jsonb_typeof(jsonb)

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

json_to_record(json)

jsonb_to_record(jsonb)

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")

json_to_recordset(json)

jsonb_to_recordset(jsonb)

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 |

json_strip_nulls(from_json json)

jsonb_strip_nulls(from_json jsonb)

json

jsonb

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]

jsonb_set(target jsonb, path text[], new_value jsonb[, create_missing boolean])

jsonb

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.

jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0,f1}','[2,3,4]', false)

jsonb_set('[{"f1":1,"f2":null},2]', '{0,f3}','[2,3,4]')

[{"f1":[2,3,4],"f2":null},2,null,3]

[{"f1": 1, "f2": null, "f3": [2, 3, 4]}, 2]

jsonb_insert(target jsonb, path text[], new_value jsonb, [insert_after boolean])

jsonb

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.

jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"')

jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"', true)

{"a": [0, "new_value", 1, 2]}

{"a": [0, 1, "new_value", 2]}

jsonb_pretty(from_json jsonb)

text

Returns from_json as indented JSON text. jsonb_pretty('[{"f1":1,"f2":null},2,null,3]')
[
    {
        "f1": 1,
        "f2": null
    },
    2,
    null,
    3
]

jsonb_path_exists(target jsonb, path jsonpath [, vars jsonb, silent bool])

boolean Checks whether JSON path returns any item for the specified JSON value.

jsonb_path_exists('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}')

true

jsonb_path_match(target jsonb, path jsonpath [, vars jsonb, silent bool])

boolean Returns JSON path predicate result for the specified JSON value. Only first result item is taken into account. If there is no results or first result item is not bool, then NULL is returned.

jsonb_path_match('{"a":[1,2,3,4,5]}', 'exists($.a[*] ? (@ >= $min && @ <= $max))', '{"min":2,"max":4}')

true

jsonb_path_query(target jsonb, path jsonpath [, vars jsonb, silent bool])

setof jsonb Gets all JSON items returned by JSON path for the specified JSON value.

select * jsonb_path_query('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}');

 jsonb_path_query
------------------
 2
 3
 4
           

jsonb_path_query_array(target jsonb, path jsonpath [, vars jsonb, silent bool])

jsonb Gets all JSON items returned by JSON path for the specified JSON value and wraps result into an array.

jsonb_path_query_array('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}')

[2, 3, 4]

jsonb_path_query_first(target jsonb, path jsonpath [, vars jsonb, silent bool])

jsonb Gets the first JSON item returned by JSON path for the specified JSON value. Returns NULL on no results.

jsonb_path_query_first('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}')

2


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 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.

Note

While the examples for the functions json_populate_record, json_populate_recordset, json_to_record and json_to_recordset 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.

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 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.

Note

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.

Note

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.

Note

The jsonb_path_exists, jsonb_path_match, jsonb_path_query, jsonb_path_query_array and jsonb_path_query_first functions have optional vars and silent argument.

When vars argument is specified, it constitutes an object contained variables to be substituted into jsonpath expression.

When silent argument is specified and has true value, the same errors are suppressed as it is in the @? and @@ operators.

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.