--- title: "json" slug: "dev-database-reference-sql-functions-json-json" updated: 2026-10-30T18:19:06Z published: 2026-10-30T18:19:06Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-json-json" --- > ## Documentation Index > Fetch the complete documentation index at: https://docs.vastdata.com/llms.txt > Use this file to discover all available pages before exploring further. # json *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Parsing and JSON functions](/develop/docs/dev-database-reference-sql-functions-json) › Build JSON.* Parses JSON text and writes it back in compact form, without the spaces and line breaks between values. Invalid JSON fails with `Malformed JSON`, so `json` also checks a document as it reads it. ## Syntax ``` json(text) ``` | Argument | Type | Description | | --- | --- | --- | | `text` | `VARCHAR` or `JSON` | A JSON document. A date, a boolean or a list is converted to JSON first. | **Returns:** `JSON`. The driver returns it as text (a Python `str`). ## Set up the examples The examples connect with the ADBC driver, as in [VAST Query Engine (ADBC)](/develop/docs/dev-database-integrations-adbc), and work in a schema called `docs_sql_fn_json_json`. Set `QE_ENDPOINT`, `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY` and `VASTDB_BUCKET` ([SQL reference](/develop/docs/dev-database-reference-sql-index#example-connect-and-use-a-transaction)), and run the blocks in order in one Python session. Below each block is the output you should see. This block connects, defines the `run()` and `plan()` helpers, and creates a table of four JSON documents stored as `VARCHAR`: an object with extra spaces, an array, an object of numbers written in different ways, and a NULL: ``` import os import re import adbc_driver_manager import adbc_driver_manager.dbapi as dbapi import adbc_driver_vastdb BUCKET = os.environ["VASTDB_BUCKET"] SCHEMA = f'"{BUCKET}/docs_sql_fn_json_json"' conn = dbapi.connect( driver=adbc_driver_vastdb.get_driver_path(), db_kwargs={ "vast.db.endpoint": os.environ["QE_ENDPOINT"], "vast.db.access_key": os.environ["AWS_ACCESS_KEY_ID"], "vast.db.secret_key": os.environ["AWS_SECRET_ACCESS_KEY"], }, autocommit=True, ) def server_message(e): """The server's message in a driver error, without the request ID or the echoed statement.""" text = re.sub(r"\[req=0x[0-9a-f]+\]: ", "", str(e)) found = (re.search(r'message: "(.*?)", request_id', text, re.S) or re.search(r"description: (.*)\)", text, re.S)) message = found.group(1) if found else text.strip().splitlines()[-1] message = re.sub(r"^Plan query: '.*?' failed with: ", "", message, flags=re.S) message = re.split(r"\\n|\n", message)[0].replace('\\"', '"') return message.replace(BUCKET, "") def run(sql): """Run one statement. Print the rows it returns, or the error.""" try: with conn.cursor() as cur: cur.execute(sql) rows = cur.fetchall() if cur.description else [] except (adbc_driver_manager.Error, OSError) as e: print(f"{type(e).__name__}: {server_message(e)}") else: print(rows) def plan(sql): """Print the plan without its ~N Rows lines: the table's row count, which can still be 0 just after an insert.""" with conn.cursor() as cur: cur.execute("EXPLAIN " + sql) steps = cur.fetchall()[0][1] print("\n".join(line for line in steps.splitlines() if "Rows" not in line)) TABLE = f"{SCHEMA}.docs" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, doc VARCHAR)") run(f"INSERT INTO {TABLE} VALUES " "(1, ' {\"user\" : \"ada\" , \"n\": 3, \"tags\": [\"a\", \"b\"] } '), " "(2, '[10, 20, [30, 40]]'), " "(3, '{\"price\": 1E2, \"zero\": -0, \"big\": 12345678901234567890}'), " "(4, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `json` reads the whole document and writes it again: - **Spaces and line breaks between values are removed.** Spaces inside strings are kept. - **Keys keep their order, and repeated keys are kept.** `json('{"a": 1, "a": 2}')` gives `{"a":1,"a":2}`. - **Numbers keep their digits,** including integers too large for `BIGINT` and values such as `1e400`. Two forms change: `1E2` becomes `100.0`, and `-0` becomes `0`. - **`\u` escapes become characters:** `"caf\u00e9"` becomes `"café"`, and a surrogate pair becomes the emoji it encodes. `\u0000` and `\t` stay escaped. - **A scalar is a document too.** `'42'`, `'"s"'`, `'true'` and `'null'` come back unchanged. ``` run("SELECT json(' {\"a\" : 1 } '), json('{\"a\": 1, \"a\": 2}'), json('{\"b\": 1, \"a\": 2}')") run("SELECT json('{\"a\": 123456789012345678901234567890}'), json('{\"a\": 1e400}'), " "json('{\"a\": 1E2}'), json('{\"a\": -0}')") run("SELECT json('{\"a\": \"caf\\u00e9\"}'), json('{\"a\": \"\\u0000x\"}')") run("SELECT json('42'), json('\"s\"'), json('true'), json('null'), typeof(json('1'))") ``` ``` [('{"a":1}', '{"a":1,"a":2}', '{"b":1,"a":2}')] [('{"a":123456789012345678901234567890}', '{"a":1e400}', '{"a":100.0}', '{"a":0}')] [('{"a":"café"}', '{"a":"\\u0000x"}')] [('42', '"s"', 'true', 'null', 'JSON')] ``` ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `'{}'`, `'[]'` | unchanged | | A `DATE`, a `BOOLEAN` or a list | converted to JSON: `"2026-10-16"`, `true`, `[1,2]` | | `''` (empty string) | Error: `Malformed JSON at byte 0 of input: input length is 0.` | | `'not json'` | Error: `Malformed JSON at byte 0 of input: invalid literal.` | | `'{'` | Error: `Malformed JSON at byte 1 of input: unexpected end of data.` | | A line break inside a string | Error: `unexpected control character in string` | | `"\ud800"` (half of a surrogate pair) | Error: `no low surrogate in string` | | A number | Error: `No function matches the given name and argument types 'json_extract(INTEGER_LITERAL, STRING_LITERAL)'` | ``` run("SELECT json(NULL), json('{}'), json('[]'), json(DATE '2026-10-16'), json(true), json([1, 2])") run("SELECT json('')") run("SELECT json('not json')") run("SELECT json('{')") run("SELECT json('{\"a\": \"line\nbreak\"}')") run("SELECT json('{\"a\": \"\\ud800\"}')") run("SELECT json(123)") ``` ``` [(None, '{}', '[]', '"2026-10-16"', 'true', '[1,2]')] OSError: Malformed JSON at byte 0 of input: input length is 0. Input: OSError: Malformed JSON at byte 0 of input: invalid literal. Input: not json OSError: Malformed JSON at byte 1 of input: unexpected end of data. Input: { OSError: Malformed JSON at byte 11 of input: unexpected control character in string. Input: {"a": "line OSError: Malformed JSON at byte 13 of input: no low surrogate in string. Input: {"a": "\ud800"} InternalError: Binder Error: No function matches the given name and argument types 'json_extract(INTEGER_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. ``` ## Examples Each document in compact form. The NULL row stays NULL: ``` run(f"SELECT id, json(doc) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '{"user":"ada","n":3,"tags":["a","b"]}'), (2, '[10,20,[30,40]]'), (3, '{"price":100.0,"zero":0,"big":12345678901234567890}'), (4, None)] ``` A document that isn't valid JSON fails the query. Add a row that isn't JSON, then filter with [json_valid](/develop/docs/dev-database-reference-sql-functions-json-json-valid) to skip it: ``` run(f"INSERT INTO {TABLE} VALUES (5, 'not json')") run(f"SELECT id, json(doc) FROM {TABLE} WHERE id = 5") run(f"SELECT id, json(doc) FROM {TABLE} WHERE json_valid(doc) ORDER BY id LIMIT 10") ``` ``` [(1,)] OSError: Malformed JSON at byte 0 of input: invalid literal. Input: not json [(1, '{"user":"ada","n":3,"tags":["a","b"]}'), (2, '[10,20,[30,40]]'), (3, '{"price":100.0,"zero":0,"big":12345678901234567890}')] ``` ## How it runs in VAST The Query Engine runs on the cluster's CNodes, and a query on a table starts with a scan in VAST DataBase (`VAST_SCAN`). VAST DataBase stores JSON as text and doesn't parse it, so `json` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the whole document and the Query Engine parses it for each row it returns. - **In `WHERE`,** a `FILTER` step in the Query Engine parses the document of every row the scan sends. ``` plan(f"SELECT id FROM {TABLE} WHERE json(doc) IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (json_extract(doc, '$') IS│ │ NOT NULL) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ doc │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store documents in compact form.** Run `json` on the documents when you write them. Then a comparison of the whole column with a compact constant, such as `doc = '[10,20,[30,40]]'`, is evaluated in VAST DataBase, without parsing; the plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE doc = '[10,20,[30,40]]'") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Validate when you write.** Check documents with [json_valid](/develop/docs/dev-database-reference-sql-functions-json-json-valid) before you insert them, so an invalid row can't stop later queries. - **Store the fields you filter on in their own columns.** See [Parsing and JSON functions](/develop/docs/dev-database-reference-sql-functions-json). ## Limitations and errors - **Invalid JSON fails the query** with `Malformed JSON at byte N of input: ...`, followed by the input. Filter the rows with [json_valid](/develop/docs/dev-database-reference-sql-functions-json-json-valid), or with a condition on another column. - **Numbers aren't accepted.** `json(123)` fails with `No function matches the given name and argument types 'json_extract(INTEGER_LITERAL, STRING_LITERAL)'`: `json` reads its argument with [json_extract](/develop/docs/dev-database-reference-sql-functions-json-json-extract). Use [to_json](/develop/docs/dev-database-reference-sql-functions-json-to-json) to turn a number into JSON. - **A `BLOB` isn't read as text.** `json('\xAA'::BLOB)` fails with `Malformed JSON at byte 0 of input: input length is 0.` Pass the document as `VARCHAR`. ``` run("SELECT to_json(123)") run("SELECT json('\\xAA'::BLOB)") ``` ``` [('123',)] OSError: Malformed JSON at byte 0 of input: input length is 0. Input: ``` ## Similar functions | Function | What it does | Result for `'{ "a" : [1, 2] }'` | | --- | --- | --- | | `json` | parses and writes compact JSON | `{"a":[1,2]}` | | `::JSON` (cast) | checks that the text is JSON and keeps it as written | `{ "a" : [1, 2] }` | | [json_pretty](/develop/docs/dev-database-reference-sql-functions-json-json-pretty) | parses and writes indented JSON, one value per line | the same document over six lines | | [json_valid](/develop/docs/dev-database-reference-sql-functions-json-json-valid) | checks without failing: `true` or `false` | `true` | | [to_json](/develop/docs/dev-database-reference-sql-functions-json-to-json) | converts a SQL value; text becomes a JSON string | `"{ \"a\" : [1, 2] }"` | ``` run("SELECT json('{ \"a\" : [1, 2] }'), '{ \"a\" : [1, 2] }'::JSON, json_pretty('{ \"a\" : [1, 2] }')") run("SELECT json_valid('{ \"a\" : [1, 2] }'), to_json('{ \"a\" : [1, 2] }')") run("SELECT 'not json'::JSON") ``` ``` [('{"a":[1,2]}', '{ "a" : [1, 2] }', '{\n "a": [\n 1,\n 2\n ]\n}')] [(True, '"{ \\"a\\" : [1, 2] }"')] OSError: Malformed JSON at byte 0 of input: invalid literal. Input: not json ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Parsing and JSON functions](/develop/docs/dev-database-reference-sql-functions-json): all the JSON functions, and [invalid JSON in a column](/develop/docs/dev-database-reference-sql-functions-json). - [json_pretty](/develop/docs/dev-database-reference-sql-functions-json-json-pretty) and [json_valid](/develop/docs/dev-database-reference-sql-functions-json-json-valid). - [Where filters run](/develop/docs/dev-database-reference-sql-select#where-filters-run) and [pushdowns](/develop/docs/dev-database-reference-pushdowns). - [EXPLAIN](/develop/docs/dev-database-reference-sql-explain): how to read a plan.