--- title: "json_array" slug: "dev-database-reference-sql-functions-json-json-array" updated: 2026-10-30T18:19:06Z published: 2026-10-30T18:19:06Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-json-json-array" --- > ## 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_array *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.* Builds a JSON array from its arguments: one element per argument, in the order given. The arguments can be of any type, and a NULL becomes `null`. ## Syntax ``` json_array(value, ...) json_array() ``` | Argument | Type | Description | | --- | --- | --- | | `value` | Any type | One element of the array. Pass as many as you need, or none. | **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_array`. 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 people. The second name holds double quotes, the third a backslash, and the last row has no values: ``` 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_array"' 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}.people" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, name VARCHAR, n BIGINT, tags VARCHAR[], joined DATE)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'ada', 3, ['a', 'b'], DATE '2026-10-16'), " "(2, 'say \"hi\"', 0, [], DATE '2026-01-01'), " "(3, 'C:\\temp', -1, ['c'], DATE '2024-02-29'), " "(4, NULL, NULL, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `json_array` writes each argument as one JSON element: | Argument | Element | Example | Result | | --- | --- | --- | --- | | Number | a JSON number | `json_array(1, 1.5)` | `[1,1.5]` | | `VARCHAR` | a JSON string | `json_array('a')` | `["a"]` | | `DATE` | a quoted string | `json_array(DATE '2026-10-16')` | `["2026-10-16"]` | | `BOOLEAN` | `true` or `false` | `json_array(true)` | `[true]` | | List | an array | `json_array([1, 2])` | `[[1,2]]` | | Struct | an object | `json_array({'a': 1})` | `[{"a":1}]` | | `JSON` value | the value itself | `json_array('{"a": 1}'::JSON)` | `[{"a":1}]` | | `NULL` | `null` | `json_array(NULL)` | `[null]` | Text that holds JSON is still text: `json_array('{"a": 1}')` gives an array holding one string, `["{\"a\": 1}"]`. Cast it to `JSON` to embed the document instead. The same cases, as the cluster returns them. They use the helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-json-json-array#set-up-the-examples): ``` run("SELECT json_array(1, 1.5), json_array('a'), json_array(DATE '2026-10-16'), json_array(true)") run("SELECT json_array([1, 2]), json_array({'a': 1}), json_array(NULL)") run("SELECT json_array('{\"a\": 1}'::JSON), json_array('{\"a\": 1}')") ``` ``` [('[1,1.5]', '["a"]', '["2026-10-16"]', '[true]')] [('[[1,2]]', '[{"a":1}]', '[null]')] [('[{"a":1}]', '["{\\"a\\": 1}"]')] ``` ## NULLs and edge cases | Input | Result | | --- | --- | | `json_array()` (no arguments) | `[]` | | `json_array(NULL, NULL)` | `[null,null]`: the result is never NULL | | `json_array(json_array(1), json_array())` | `[[1],[]]` | | A string with `"` or `\` \| escaped as `\"` and `\\` | | | A string with a tab or a control character | escaped as `\t` or `\u0001` | | `'</script>'` | `"</script>"`, unchanged | ``` run("SELECT json_array(), json_array(NULL, NULL), json_array(json_array(1), json_array())") run("SELECT json_array('a\"b\\c', 'tab\there', chr(1), '')") ``` ``` [('[]', '[null,null]', '[[1],[]]')] [('["a\\"b\\\\c","tab\\there","\\u0001",""]',)] ``` ## Examples One array per row, built from three columns. The quotes in row 2 and the backslash in row 3 are escaped, and the empty row gives `[4,null,null]`: ``` run(f"SELECT id, json_array(id, name, n) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '[1,"ada",3]'), (2, '[2,"say \\"hi\\"",0]'), (3, '[3,"C:\\\\temp",-1]'), (4, '[4,null,null]')] ``` A list column becomes a nested array and a date a quoted string: ``` run(f"SELECT id, json_array(name, tags, joined) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '["ada",["a","b"],"2026-10-16"]'), (2, '["say \\"hi\\"",[],"2026-01-01"]'), (3, '["C:\\\\temp",["c"],"2024-02-29"]'), (4, '[null,null,null]')] ``` ## 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`). `json_array` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the columns and the Query Engine builds the array for each row it returns. - **In `WHERE`,** a `FILTER` step in the Query Engine builds the array for every row the scan sends. Because the result is never NULL, `json_array(...) IS NOT NULL` keeps every row. ``` plan(f"SELECT id FROM {TABLE} WHERE json_array(n, name) IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #2 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (json_array(n, name) IS │ │ NOT NULL) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ n │ │ name │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Filter on the columns, not on the array.** A comparison of a column with a constant, such as `id = 2`, is evaluated in VAST DataBase, so only the matching rows reach the Query Engine to be turned into JSON. The plan has no `FILTER` step: ``` plan(f"SELECT json_array(id, name) FROM {TABLE} WHERE id = 2") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ json_array(id, name) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ id │ │ name │ │ │ └───────────────────────────┘ ``` - **Build only what you return.** Each `json_array` call in the `SELECT` list is computed for every returned row. ## Limitations and errors - **One array per row.** There's no aggregate that collects rows into one array: `json_group_array` fails with `The operator 'UNGROUPED_AGGREGATE' type=8 is currently not supported for this usage.`, and `to_json(list(id))` fails with `The operator 'HASH_GROUP_BY' type=9 is currently not supported.` Read the rows with your client and build the array there. - **Text isn't parsed.** A `VARCHAR` argument is always written as a JSON string. Cast it with `::JSON` to embed it as JSON. ``` run(f"SELECT json_group_array(id) FROM {TABLE}") run(f"SELECT to_json(list(id)) FROM {TABLE}") ``` ``` InternalError: The operator 'UNGROUPED_AGGREGATE' type=8 is currently not supported for this usage. InternalError: The operator 'HASH_GROUP_BY' type=9 is currently not supported. ``` ## Similar functions | Function | What it builds | Result for a list `[1, 2]` | | --- | --- | --- | | `json_array(1, 2)` | an array from separate arguments | `[1,2]` | | [to_json](/develop/docs/dev-database-reference-sql-functions-json-to-json) | JSON from one value of any type | `[1,2]` | | [array_to_json](/develop/docs/dev-database-reference-sql-functions-json-array-to-json) | JSON from one list | `[1,2]` | | [json_quote](/develop/docs/dev-database-reference-sql-functions-json-json-quote) | JSON from one value of any type | `[1,2]` | | [json_object](/develop/docs/dev-database-reference-sql-functions-json-json-object) | an object from key-value pairs | (not for lists) | ``` run("SELECT json_array(1, 2), to_json([1, 2]), array_to_json([1, 2]), json_quote([1, 2])") ``` ``` [('[1,2]', '[1,2]', '[1,2]', '[1,2]')] ``` 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. - [json_object](/develop/docs/dev-database-reference-sql-functions-json-json-object) and [to_json](/develop/docs/dev-database-reference-sql-functions-json-to-json). - [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.