--- title: "list_append" slug: "dev-database-reference-sql-functions-lists-list-append" updated: 2026-10-30T18:19:06Z published: 2026-10-30T18:19:06Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-lists-list-append" --- > ## 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. # list_append *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [List, struct and map functions](/develop/docs/dev-database-reference-sql-functions-lists-and-structs) › Combine and change lists.* Returns a list with one element added at the end. `array_append` and `array_push_back` are the same function. ## Syntax ``` list_append(list, element) array_append(list, element) array_push_back(list, element) ``` | Argument | Type | Description | | --- | --- | --- | | `list` | A list of any type | The list to add to. | | `element` | A value of the list's element type | The value to add at the end. For a list of lists, a list. | **Returns:** a list of the common type of the list's elements and `element`. **Aliases:** `array_append`, `array_push_back`. ## 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_lists_list_append`. 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 orders, each with a list of item numbers (`items`), a list of labels (`labels`) and the next item to add (`next_item`). Order 2 has a NULL item and no next item, order 3 has empty lists, and order 4 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_lists_list_append"' 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}.orders" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, items BIGINT[], labels VARCHAR[], next_item BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, [1, 2, 3], ['new', 'paid'], 7), " "(2, [3, NULL, 3], ['paid'], NULL), " "(3, [], [], 0), " "(4, NULL, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `list_append` adds `element` after the last element of `list`: `list_append([1, 2], 3)` is `[1, 2, 3]`. It's defined as `list_concat(list, [element])`, so it behaves like [list_concat](/develop/docs/dev-database-reference-sql-functions-lists-list-concat) with a one-element list, and errors about argument types name `list_concat`. The element and the list's elements are brought to a common type: `list_append([1, 2], 2.5)` is a `DECIMAL(11,1)[]` list, `[1.0, 2.0, 2.5]`. On a list of lists, the element is a list: `list_append([[1]], [2, 3])` is `[[1], [2, 3]]`. It doesn't change the table: it returns a new list for each row. ## NULLs and edge cases | Input | Result | | --- | --- | | `list_append(NULL, 9)` (a NULL list) | `[9]`: a NULL list counts as empty | | `list_append(NULL::BIGINT[], 1)` | `[1]` | | `list_append([1, 2], NULL)` | `[1, 2, NULL]` | | `list_append(NULL, NULL)` | `[NULL]` | | `list_append([], 1)` | `[1]` | | `list_append([1, 2], 2.5)` | `[1.0, 2.0, 2.5]`, a `DECIMAL(11,1)[]` | | `list_append([[1]], [2, 3])` | `[[1], [2, 3]]` | | `list_append([1, 2], 'x')` | Error: `Cannot concatenate lists of types INTEGER[] and VARCHAR[] - an explicit cast is required` | | `list_append([1], [2])` | Error: `Cannot concatenate lists of types INTEGER[] and INTEGER[][] - an explicit cast is required` | | A number, string, date, boolean or `BLOB` as `list` | Error: `No function matches the given name and argument types`, for example `'list_concat(INTEGER_LITERAL, INTEGER[])'` | | Three arguments | Error: `Macro function list_append(l, e) requires 2 positional arguments, but 3 positional arguments were provided.` | The same cases, as the cluster returns them. They use the helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-lists-list-append#set-up-the-examples): ``` run("SELECT list_append(NULL, 9), list_append(NULL::BIGINT[], 1), list_append([1, 2], NULL), " "list_append(NULL, NULL), list_append([], 1)") run("SELECT list_append([1, 2], 2.5), typeof(list_append([1, 2], 2.5)), list_append([[1]], [2, 3])") run("SELECT list_append([1, 2], 'x')") run("SELECT list_append([1], [2])") run("SELECT list_append(123, 9)") run("SELECT list_append([1], 2, 3)") ``` ``` [([9], [1], [1, 2, None], [None], [1])] [([Decimal('1.0'), Decimal('2.0'), Decimal('2.5')], 'DECIMAL(11,1)[]', [[1], [2, 3]])] InternalError: Binder Error: Cannot concatenate lists of types INTEGER[] and VARCHAR[] - an explicit cast is required InternalError: Binder Error: Cannot concatenate lists of types INTEGER[] and INTEGER[][] - an explicit cast is required InternalError: Binder Error: No function matches the given name and argument types 'list_concat(INTEGER_LITERAL, INTEGER[])'. You might need to add explicit type casts. InternalError: Binder Error: Macro function list_append(l, e) requires 2 positional arguments, but 3 positional arguments were provided. ``` ## Examples Add item 9 to every order, and the label `'shipped'`. Order 4 has NULL lists, so it gets a list of one element: ``` run(f"SELECT id, list_append(items, 9), list_append(labels, 'shipped') FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, [1, 2, 3, 9], ['new', 'paid', 'shipped']), (2, [3, None, 3, 9], ['paid', 'shipped']), (3, [9], ['shipped']), (4, [9], ['shipped'])] ``` Add each order's own `next_item`. Order 2 has no next item, so a NULL element is added; order 4 has neither, so the result is `[NULL]`. `array_append` and `array_push_back` give the same lists: ``` run(f"SELECT id, list_append(items, next_item), array_append(items, next_item), array_push_back(items, next_item) " f"FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, [1, 2, 3, 7], [1, 2, 3, 7], [1, 2, 3, 7]), (2, [3, None, 3, None], [3, None, 3, None], [3, None, 3, None]), (3, [0], [0], [0]), (4, [None], [None], [None])] ``` Keep the orders that have more than three items once item 9 is added: ``` run(f"SELECT id FROM {TABLE} WHERE len(list_append(items, 9)) > 3 ORDER BY id LIMIT 10") ``` ``` [(1,), (2,)] ``` ## 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`). The scan reads a list column whole, and VAST DataBase doesn't evaluate list functions, so `list_append()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the list column and the Query Engine computes `list_append()` for each row it returns. - **In `WHERE`,** the scan sends the list for every row, and a `FILTER` step in the Query Engine computes the condition and keeps the rows that match. No rows are skipped in storage. The plan of the `WHERE` example shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE len(list_append(items, 9)) > 3") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (len(list_concat(items, [9│ │ ])) > 3) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ items │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Pair a list condition with a pushed-down condition.** In `id > 1 AND len(list_append(items, 9)) > 3`, `id > 1` is evaluated in VAST DataBase, so the list condition runs only on the rows that pass it. The `FILTER` step in the plan holds only the list condition: ``` plan(f"SELECT id FROM {TABLE} WHERE id > 1 AND len(list_append(items, 9)) > 3") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #0 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (len(list_concat(items, [9│ │ ])) > 3) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ id │ │ items │ │ │ └───────────────────────────┘ ``` - **Filter on the stored list, not the appended one.** `len(list_append(items, 9)) > 3` is the same as `len(items) > 2` for a non-NULL list; the shorter condition saves building a new list for every row. - **Keep values you filter on outside lists.** If you often test a list's length, store it in its own column when you write the rows, so the filter can be pushed down. ## Limitations and errors - **One element at a time.** A third argument fails with `Macro function list_append(l, e) requires 2 positional arguments, but 3 positional arguments were provided.` To add several elements, use [list_concat](/develop/docs/dev-database-reference-sql-functions-lists-list-concat) with a list of them. - **The element must match the list's type.** A string added to an `INTEGER[]` fails with `Cannot concatenate lists of types INTEGER[] and VARCHAR[] - an explicit cast is required`. Cast the element, or the list, to a common type. - **The first argument must be a list.** A number, string, date, boolean or `BLOB` fails with `No function matches the given name and argument types 'list_concat(...)'`. - **A NULL list counts as empty.** `list_append(NULL, 9)` is `[9]`, not NULL. If a NULL list should stay NULL, test it first: `CASE WHEN items IS NULL THEN NULL ELSE list_append(items, 9) END`. ``` run(f"SELECT id, CASE WHEN items IS NULL THEN NULL ELSE list_append(items, 9) END FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, [1, 2, 3, 9]), (2, [3, None, 3, 9]), (3, [9]), (4, None)] ``` ## Similar functions | Function | Result for `[1, 2]` and `3` | Result with a NULL list | | --- | --- | --- | | `list_append([1, 2], 3)` | `[1, 2, 3]` | `list_append(NULL, 9)`: `[9]` | | [list_concat](/develop/docs/dev-database-reference-sql-functions-lists-list-concat): `list_concat([1, 2], [3])` | `[1, 2, 3]` | `list_concat(NULL, [9])`: `[9]` | | `\|\|`: `[1, 2] \|\| [3]` | `[1, 2, 3]` | `NULL \|\| [9]`: `NULL` | | [list_prepend](/develop/docs/dev-database-reference-sql-functions-lists-list-prepend): `list_prepend(0, [1, 2])`, adds at the start | `[0, 1, 2]` | `list_prepend(9, NULL)`: `[9]` | | [flatten](/develop/docs/dev-database-reference-sql-functions-lists-flatten): `flatten([[1, 2], [3]])` | `[1, 2, 3]` | `flatten([NULL, [9]])`: `[9]` | ``` run("SELECT list_append([1, 2], 3), list_concat([1, 2], [3]), [1, 2] || [3], list_prepend(0, [1, 2]), " "flatten([[1, 2], [3]])") run("SELECT list_append(NULL, 9), list_concat(NULL, [9]), NULL || [9], list_prepend(9, NULL), flatten([NULL, [9]])") ``` ``` [([1, 2, 3], [1, 2, 3], [1, 2, 3], [0, 1, 2], [1, 2, 3])] [([9], [9], None, [9], [9])] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [list_prepend](/develop/docs/dev-database-reference-sql-functions-lists-list-prepend): add an element at the start. - [List, struct and map functions](/develop/docs/dev-database-reference-sql-functions-lists-and-structs): all the list functions. - [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.