---
title: "list_count"
slug: "dev-database-reference-sql-functions-lists-list-count"
updated: 2026-10-30T18:19:06Z
published: 2026-10-30T18:19:06Z
canonical: "docs.vastdata.com/dev-database-reference-sql-functions-lists-list-count"
---

> ## 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_count

*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) › Aggregate a list.* Returns the number of elements in a list that aren't NULL. To count every element, NULLs included, use [len](/develop/docs/dev-database-reference-sql-functions-lists-array-length).

## Syntax

```
list_count(l)
```

| Argument | Type | Description |
| --- | --- | --- |
| `l` | a list of any type | The list whose non-NULL elements are counted. |

**Returns:** `BIGINT`.

## 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_count`. 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 five rows of lists: numbers, words, measurements, flags and lists of lists. Row 3 has empty lists and row 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_count"'

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, "<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}.samples"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, nums BIGINT[], words VARCHAR[], vals DOUBLE[], "
    "flags BOOLEAN[], nested BIGINT[][])")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, [1, 2, 3], ['a', 'b', 'c'], [0.5, 2.5, -1.0], [true, false, true], [[1, 2], [3]]), "
    "(2, [3, NULL, 3], ['b', NULL, 'B'], [2.0, NULL], [NULL, true], [[], NULL, [4]]), "
    "(3, [], [], [], [], []), "
    "(4, NULL, NULL, NULL, NULL, NULL), "
    "(5, [-5, 0, -5, 10], ['\u00e9', 'Zo\u00eb', '\U0001F1EB\U0001F1F7', ''], [1e308, 1e308, -1e-308], "
    "[false, false], [[5, NULL], [], [6, 7, 8]])")
```

```
[]
[]
[(5,)]
```

## What it does

`list_count(l)` counts the elements of `l` that aren't NULL:

- `[1, NULL, 3]` has 2, and `[NULL]` has 0.
- An empty list has 0. A NULL list returns NULL, not 0.
- In a list of lists, an empty inner list is an element like any other: `list_count([[], NULL])` is `1`.
- Duplicates count each time. To count distinct values, use [list_unique](/develop/docs/dev-database-reference-sql-functions-lists-list-unique).

`list_count(l)` gives the same result as [list_aggregate](/develop/docs/dev-database-reference-sql-functions-lists-list-aggregate)`(l, &apos;count&apos;)`.

## NULLs and edge cases

| Input | Result |
| --- | --- |
| `NULL` | `NULL` |
| `[]` | `0` |
| `[NULL]` | `0` |
| `[1, NULL, 3]` | `2` |
| `[[], NULL]` | `1` |
| `typeof(list_count([1]))` | `&apos;BIGINT&apos;` |
| A number, string, `BLOB`, date or boolean | Error: `No function matches the given name and argument types`, for example `&apos;list_aggr(INTEGER_LITERAL, STRING_LITERAL)&apos;` |

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-count#set-up-the-examples):

```
run("SELECT list_count(NULL), list_count([]::BIGINT[]), list_count([NULL]::BIGINT[]), list_count([1, NULL, 3])")
run("SELECT list_count([[], NULL]), typeof(list_count([1]))")
run("SELECT list_count(123)")
```

```
[(None, 0, 0, 2)]
[(1, 'BIGINT')]
InternalError: Binder Error: No function matches the given name and argument types 'list_aggr(INTEGER_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts.
```

## Examples

The number of non-NULL elements in each list of the table. Row 2's NULL elements aren't counted; row 3's empty lists count 0 and row 4's NULL lists return NULL:

```
run(f"SELECT id, list_count(nums), list_count(words), list_count(vals), list_count(flags), list_count(nested) "
    f"FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 3, 3, 3, 3, 2), (2, 2, 2, 1, 1, 2), (3, 0, 0, 0, 0, 0), (4, None, None, None, None, None), (5, 4, 4, 3, 2, 3)]
```

The rows whose numbers include a NULL: there, `list_count` is smaller than `len`:

```
run(f"SELECT id, nums FROM {TABLE} WHERE list_count(nums) < len(nums) ORDER BY id LIMIT 10")
```

```
[(2, [3, None, 3])]
```

## 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 `list_count()` always runs in the Query Engine:

- **In the `SELECT` list,** a projection step computes `list_count()` for each row the scan returns.
- **In `WHERE`,** the scan sends the list for every row, and a `FILTER` step computes `list_count()` and keeps the rows that match. No rows are skipped in storage.

The plan of a `WHERE` condition on `list_count()` shows the `FILTER` step above the scan:

```
plan(f"SELECT id FROM {TABLE} WHERE list_count(nums) IS NOT NULL")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│ (list_aggr(nums, 'count') │
│        IS NOT NULL)       │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│            nums           │
│             id            │
│                           │
└───────────────────────────┘
```

## Make it faster

- **Add a condition on a plain column.** A comparison of a column with a constant, such as `id &gt; 1`, is evaluated in VAST DataBase, so `list_count()` runs only on the rows that pass it. The plan for `id &gt; 1` alone has no `FILTER` step:

```
plan(f"SELECT id FROM {TABLE} WHERE id > 1")
```

```
┌───────────────────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│      Projections: id      │
│                           │
└───────────────────────────┘
```

- **Store the count if you filter on it often.** Compute it when you write the rows and keep it in its own column: `num_count &gt; 2` is pushed down, `list_count(nums) &gt; 2` isn't.

## Limitations and errors

- **Lists only.** Any other type fails with `No function matches the given name and argument types`. The error names `list_aggr`, the function `list_count` calls, and its accepted form `list_aggr(ANY[], VARCHAR, [ANY...]) -&gt; ANY`.
- **`ORDER BY` needs a `LIMIT`.** Without one, the query fails with `The operator &apos;ORDER_BY&apos; type=1 is currently not supported for this usage`.

## Similar functions

| Function | What it counts | Result for `[3, 1, NULL, 3, 10]` |
| --- | --- | --- |
| `list_count` | non-NULL elements | `4` |
| [list_aggregate](/develop/docs/dev-database-reference-sql-functions-lists-list-aggregate)`(l, &apos;count&apos;)` | the same as `list_count` | `4` |
| `len` ([array_length](/develop/docs/dev-database-reference-sql-functions-lists-array-length)) | all elements, NULLs included | `5` |
| [list_unique](/develop/docs/dev-database-reference-sql-functions-lists-list-unique) | distinct non-NULL values | `3` |

```
run("SELECT list_count(l), list_aggregate(l, 'count'), len(l), list_unique(l) FROM (SELECT [3, 1, NULL, 3, 10] AS l)")
```

```
[(4, 4, 5, 3)]
```

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.