--- title: "bit_count" slug: "dev-database-reference-sql-functions-binary-hash-uuid-bit-count" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-bit-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. # bit_count *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Binary, hash and UUID functions](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid) › Bit strings.* Returns the number of bits set to 1 in a `BIT` value, or in the two's-complement form of an integer: `bit_count('101101'::BIT)` is `4`. ## Syntax ``` bit_count(x) ``` | Argument | Type | Description | | --- | --- | --- | | `x` | `BIT`, or an integer: `TINYINT`, `SMALLINT`, `INTEGER`, `BIGINT`, `HUGEINT` (`UTINYINT` and `UBIGINT` also work) | The value whose set bits to count. | **Returns:** `BIGINT` for a `BIT` value; `TINYINT` for an integer. ## 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_binary_hash_uuid_bit_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 feature-flag sets. Each is stored twice: as a `VARCHAR` of 0s and 1s, and as an `INTEGER` permission mask. The third 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_binary_hash_uuid_bit_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, "") 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}.flags" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, bits VARCHAR, perms INTEGER)") run(f"INSERT INTO {TABLE} VALUES " "(1, '1011', 11), " "(2, '0', 0), " "(3, NULL, NULL), " "(4, '10000000', 128), " "(5, '0110', -1)") ``` ``` [] [] [(5,)] ``` ## What it does `bit_count` counts the 1s: | Argument type | What it counts | Example | Result | | --- | --- | --- | --- | | `BIT` | the 1s in the bit string | `bit_count('101101'::BIT)` | `4` | | An integer | the 1s in its two's-complement form, at the width of its type | `bit_count(255)` | `8` | | A negative integer | the same: all the bits are 1 for `-1` | `bit_count(-1)` (an `INTEGER`) | `32` | The width matters for negative numbers: `-1` has 8 bits set as a `TINYINT`, 16 as a `SMALLINT`, 32 as an `INTEGER` and 64 as a `BIGINT`. A whole-number literal such as `-1` is an `INTEGER`. A `VARCHAR` column must be cast to `BIT` first: `bit_count(CAST(bits AS BIT))`. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `'0'::BIT` | `0` | | A `BIT` value of 1,000 ones | `1000` | | `bit_count(123)` | `6` | | `bit_count(-1::TINYINT)`, `bit_count(-1::BIGINT)` | `8`, `64` | | `bit_count(-128::TINYINT)` | Error: `Type INT32 with value 128 can't be cast because the value is out of range for the destination type INT8`; the cast applies to `128` before the minus | | `bit_count('5')` (a string literal) | Error: `Could not choose a best candidate function for the function call "bit_count(STRING_LITERAL)"` | | A decimal, `DOUBLE`, `BOOLEAN`, date or `VARCHAR` column | Error: `No function matches the given name and argument types`, for example `'bit_count(DECIMAL(2,1))'` | 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-binary-hash-uuid-bit-count#set-up-the-examples): ``` run("SELECT bit_count(NULL), bit_count('0'::BIT), bit_count(CAST(repeat('1', 1000) AS BIT)), bit_count(123), " "bit_count(-1::TINYINT), bit_count(-1::BIGINT)") run("SELECT bit_count(-128::TINYINT)") run("SELECT bit_count('5')") run("SELECT bit_count(1.5)") ``` ``` [(None, 0, 1000, 6, 8, 64)] OSError: Type INT32 with value 128 can't be cast because the value is out of range for the destination type INT8 InternalError: Binder Error: Could not choose a best candidate function for the function call "bit_count(STRING_LITERAL)". In order to select one, please add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'bit_count(DECIMAL(2,1))'. You might need to add explicit type casts. ``` ## Examples The number of flags set in each row, from the bit string and from the integer mask. `-1` as an `INTEGER` has all 32 bits set: ``` run(f"SELECT id, bits, bit_count(CAST(bits AS BIT)), perms, bit_count(perms) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '1011', 3, 11, 3), (2, '0', 0, 0, 0), (3, None, None, None, None), (4, '10000000', 1, 128, 1), (5, '0110', 2, -1, 32)] ``` Keep the rows with more than two flags set: ``` run(f"SELECT id, bits FROM {TABLE} WHERE bit_count(CAST(bits AS BIT)) > 2 ORDER BY id LIMIT 10") ``` ``` [(1, '1011')] ``` ## 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 can evaluate a comparison of a column with a constant, but not a function of a column, so `bit_count()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `bit_count()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `bit_count()` 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 bit_count(CAST(bits AS BIT)) > 2") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (bit_count(CAST(bits AS │ │ BIT)) > 2) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ bits │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store the count if you filter on it often.** Compute it when you write the rows and keep it in its own column: `flag_count > 2` is pushed down to VAST DataBase, `bit_count(CAST(bits AS BIT)) > 2` isn't. The plan for a raw column compared with a constant has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE perms > 2") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Combine it with a pushed-down condition.** In `id > 100 AND bit_count(perms) > 2`, `id > 100` is still evaluated in VAST DataBase, so `bit_count()` runs only on the rows that pass it. ## Limitations and errors - **`HUGEINT` counts above 127 wrap.** The result for an integer is a `TINYINT`, so a `HUGEINT` with 128 bits set returns `-128`: `bit_count(-1::HUGEINT)` is `-128`, not `128`. For a `HUGEINT` that can be negative, count the bits of its cast to `BIT`, which returns a `BIGINT`. ``` run("SELECT bit_count(-1::HUGEINT), bit_count(CAST(-1::HUGEINT AS BIT))") ``` ``` [(-128, 128)] ``` - **Not for `UHUGEINT` or `VARINT`.** They fail with `No function matches the given name and argument types`. - **Not for strings, decimals or floating-point numbers.** A `VARCHAR` column, a `DECIMAL`, a `DOUBLE`, a `BOOLEAN` or a date fails with `No function matches the given name and argument types`. The error lists the types `bit_count` accepts. Cast a `VARCHAR` of 0s and 1s to `BIT` first. - **Negative literals of a small type need parentheses.** `-128::TINYINT` casts `128` and then negates it, and `128` doesn't fit in a `TINYINT`. Write `(-128)::TINYINT`. ## Similar functions | Function | Result for `'101101'::BIT` (`bit_count` gives `4`) | | --- | --- | | [length](/develop/docs/dev-database-reference-sql-functions-string-length) and [bit_length](/develop/docs/dev-database-reference-sql-functions-string-bit-length): all the bits | `6` | | [octet_length](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-octet-length): the bytes the bits fill | `1` | | [get_bit](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-get-bit)`(bits, 0)`: the first bit | `1` | | [bit_position](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bit-position)`('1'::BIT, bits)`: where the first 1 is | `1` | ``` run("SELECT bit_count('101101'::BIT), length('101101'::BIT), bit_length('101101'::BIT), " "octet_length('101101'::BIT), get_bit('101101'::BIT, 0), bit_position('1'::BIT, '101101'::BIT)") ``` ``` [(4, 6, 6, 1, 1, 1)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Binary, hash and UUID functions](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid#bit-strings): all the bit string functions. - [BIT values and casts](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bit-values). - [Where filters run](/develop/docs/dev-database-reference-sql-select#where-filters-run) and [pushdowns](/develop/docs/dev-database-reference-pushdowns).