Presto 0.100 Documentation

5.10. JSON函数

5.10. JSON函数

json_array_contains(json, value) → boolean

判断value是否在json(json格式的字符串)中存在:

SELECT json_array_contains('[1, 2, 3]', 2);
json_array_length(json) → bigint

Returns the array length of json (a string containing a JSON array).

SELECT json_array_length('[1, 2, 3]');
json_extract(json, json_path) → varchar

Evaluates the JSONPath-like expression json_path on json (a string containing JSON) and returns the result as a JSON string.

SELECT json_extract(json, '$.store.book');
json_extract_scalar(json, json_path) → varchar

Like json_extract(), but returns the result value as a string (as opposed to being encoded as JSON). The value referenced by json_path must be a scalar (boolean, number or string).

SELECT json_extract_scalar('[1, 2, 3]', '$[2]');

SELECT json_extract_scalar(json, '$.store.book[0].author');
json_array_get(json_array, index) → varchar

Returns the element at the specified index into the json_array. The index is 0-based. For example:

SELECT json_array_get('["a", "b", "c"]', 0); => "a"
SELECT json_array_get('["a", "b", "c"]', 1); => "b"

This function also supports negative indexes for fetching element indexed from the end of an array. For example:

SELECT json_array_get('["c", "b", "a"]', -1); => "a"
SELECT json_array_get('["c", "b", "a"]', -2); => "b"

If the element at the specified index doesn’t exist, the function returns null:

SELECT json_array_get('[]', 0); => null
SELECT json_array_get('["a", "b", "c"]', 10); => null
SELECT json_array_get('["c", "b", "a"]', -10); => null
json_size(json, json_path) → bigint

Like json_extract(), but returns the size of the value. The size of an object value is the number of fields and the size of an array is the number of elements. The size of a scalar value is zero. For example:

SELECT json_size('{ "x": {"a": 1, "b": 2} }', '$.x'); => 2
SELECT json_size('{ "x": [1, 2, 3] }', '$.x'); => 2
SELECT json_size('{ "x": {"a": 1, "b": 2} }', '$.x.a'); => 0