--- title: "list_position" slug: "dev-database-reference-sql-functions-lists-list-position" updated: 2026-10-30T18:19:06Z published: 2026-10-30T18:19:06Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-lists-list-position" --- > ## 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_position *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) › Search a list.* Returns the position, counted from 1, of the first element of a list that equals a value, or NULL if no element does. `list_indexof`, `array_position` and `array_indexof` are the same function. ## Syntax ``` list_position(list, element) list_indexof(list, element) array_position(list, element) array_indexof(list, element) ``` | Argument | Type | Description | | --- | --- | --- | | `list` | a list of any element type | The list to search. | | `element` | the list's element type, or one that converts to it | The value to look for. | **Returns:** `INTEGER`: the position of the first match, starting at 1, or `NULL` if there's none. **Aliases:** `list_indexof`, `array_position`, `array_indexof`. ## 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_position`. 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 delivery routes, each with its list of stops in order and a list of stop numbers. Route 2 has a NULL stop number, route 3 has no stops, 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_lists_list_position"' 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}.routes" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, stops VARCHAR[], stop_ids BIGINT[])") run(f"INSERT INTO {TABLE} VALUES " "(1, ['depot', 'mill', 'port', 'depot'], [10, 20, 30, 10]), " "(2, ['port', 'depot'], [30, NULL]), " "(3, [], []), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `list_position` looks for the first element of `list` that equals `element` and returns its position. Positions start at 1, as in [list_extract](/develop/docs/dev-database-reference-sql-functions-lists-list-extract) and `l[i]`, so `l[list_position(l, x)]` is `x` when `x` is in the list. - **The first match wins.** `list_position([5, 5], 5)` is `1`. - **No match gives NULL,** not `0`: test the result with `IS NOT NULL`. - **The comparison is exact and typed,** as in [list_contains](/develop/docs/dev-database-reference-sql-functions-lists-list-contains): case-sensitive for strings, by value for numbers (`2.0` is found at position 2 of `[1, 2]`), whole elements for nested lists, and `NaN` finds `NaN`. ## NULLs and edge cases | Input | Result | | --- | --- | | A NULL list: `list_position(NULL, 3)` | `NULL` | | A NULL `element`: `list_position([1, 2], NULL)` | `NULL` | | `list_position([1, NULL], NULL)` | `NULL`: a NULL element can't be found | | `list_position([1, 2, 3], 42)` (not in the list) | `NULL` | | `list_position([], 1)` (empty list) | `NULL` | | `list_position([5, 5], 5)` | `1` | | `list_position([1, 2], 2.0)` | `2` | | `list_position(['a', 'b'], 'B')` | `NULL` | | `list_position([[1], [2]], [2])` | `2` | | `list_position([1.0, 'NaN'::DOUBLE], 'NaN'::DOUBLE)` | `2` | | `list_position([1, 2], 'a')` (a value of another type) | Error: `list_position: Cannot match element of type 'VARCHAR' in a list of type 'INTEGER[]' - an explicit cast is required` | The same cases, as the cluster returns them. They use the table and helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-lists-list-position#set-up-the-examples): ``` run("SELECT list_position(NULL, 3), list_position([1, 2], NULL), list_position([1, NULL], NULL), " "list_position([1, 2, 3], 42), list_position([], 1), list_position([5, 5], 5)") run("SELECT list_position([1, 2], 2.0), list_position(['a', 'b'], 'B'), list_position([[1], [2]], [2]), " "list_position([1.0, 'NaN'::DOUBLE], 'NaN'::DOUBLE)") run("SELECT list_position([1, 2], 'a')") ``` ``` [(None, None, None, None, None, 1)] [(2, None, 2, 2)] InternalError: Binder Error: list_position: Cannot match element of type 'VARCHAR' in a list of type 'INTEGER[]' - an explicit cast is required ``` ## Examples Where each route first stops at the depot and at stop 30. Route 1 visits the depot twice; the first visit counts: ``` run(f"SELECT id, list_position(stops, 'depot'), array_position(stop_ids, 30) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 1, 3), (2, 2, 1), (3, None, None), (4, None, None)] ``` The routes that stop at the port, and the stop right after it. If the port were a route's last stop, the result would be NULL, because a position past the end of a list gives NULL: ``` run(f"SELECT id, stops[list_position(stops, 'port') + 1] FROM {TABLE} " f"WHERE list_position(stops, 'port') IS NOT NULL ORDER BY id LIMIT 10") ``` ``` [(1, 'depot'), (2, 'depot')] ``` ## 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 list columns whole, and every condition on a list, `list_position()` included, runs in the Query Engine: - **In the `SELECT` list,** the scan sends the list column and the Query Engine searches it for each row it returns. - **In `WHERE`,** the scan sends the list for every row, and a `FILTER` step in the Query Engine searches it and keeps the rows that match. No rows are skipped in storage. The plan of a `WHERE` on the position shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE list_position(stops, 'port') IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (list_position(stops, │ │ 'port') IS NOT NULL) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ stops │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **To test membership, use list_contains.** `list_position(l, x) IS NOT NULL` and `list_contains(l, x)` keep the same rows; `list_contains` says what you mean and returns a `BOOLEAN`. - **Pair it with a pushed-down condition.** A comparison of a plain column with a constant, such as `id > 1`, is evaluated in VAST DataBase, so the rows it rules out never reach the `FILTER` step. ``` run(f"SELECT id FROM {TABLE} WHERE id > 1 AND list_contains(stops, 'port') ORDER BY id LIMIT 10") ``` ``` [(2,)] ``` ## Limitations and errors - **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`, for example `'list_position(STRING_LITERAL, STRING_LITERAL)'`. To find a substring, use [strpos](/develop/docs/dev-database-reference-sql-functions-string-strpos). - **The value must match the element type.** Otherwise the call fails with `Cannot match element of type ... - an explicit cast is required`. - **Only the first match, and never a NULL.** `list_position` returns one position, and a NULL element can't be found. To test for NULL elements, see [list_contains](/develop/docs/dev-database-reference-sql-functions-lists-list-contains#limitations-and-errors). ``` run("SELECT list_position('abc', 'b')") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'list_position(STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. ``` ## Similar functions | Function | Returns | Result for `[3, 1, NULL, 3, 10]` and `3` | | --- | --- | --- | | `list_position(l, 3)` | the first position of 3 | `1` | | [list_contains](/develop/docs/dev-database-reference-sql-functions-lists-list-contains)`(l, 3)` | whether 3 is an element | `true` | | [list_extract](/develop/docs/dev-database-reference-sql-functions-lists-list-extract)`(l, 2)`, `l[2]` | the element at position 2 (the inverse) | `1` | | `list_position(l, NULL)` | NULL can't be found | `NULL` | ``` run("SELECT list_position(l, 3), list_contains(l, 3), list_extract(l, 2), l[2], list_position(l, NULL) " "FROM (SELECT [3, 1, NULL, 3, 10] AS l)") ``` ``` [(1, True, 1, 1, None)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [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.