--- title: "bitstring" slug: "dev-database-reference-sql-functions-binary-hash-uuid-bitstring" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-bitstring" --- > ## 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. # bitstring *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 a `BIT` value of a given length, made from a shorter bit string padded on the left with 0s: `bitstring('101', 8)` is `'00000101'`. ## Syntax ``` bitstring(bits, length) ``` | Argument | Type | Description | | --- | --- | --- | | `bits` | `VARCHAR` of 0s and 1s, or `BIT` | The bits to pad. | | `length` | `INTEGER` | The length of the result, in bits. It must be at least the length of `bits`. | **Returns:** `BIT`. ## 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_bitstring`. 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, stored as `VARCHAR` strings of 0s and 1s of different lengths. 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_bitstring"' 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)") run(f"INSERT INTO {TABLE} VALUES " "(1, '1011'), " "(2, '0'), " "(3, NULL), " "(4, '10000000'), " "(5, '0110')") ``` ``` [] [] [(5,)] ``` ## What it does `bitstring` adds 0s to the left of `bits` until the result is `length` bits long. A `length` equal to the length of `bits` returns the same bits. The first argument can be a `VARCHAR` of 0s and 1s, including a `VARCHAR` column, or a `BIT` value; the result is a `BIT` value, so cast it to `VARCHAR` to read it. Use it to bring bit strings of different lengths to one length, for example before you combine them with the [bitwise operators](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bitwise-operators-on-bit), which need operands of the same length. ## NULLs and edge cases | Input | Result | | --- | --- | | `bitstring(NULL, 20)`, `bitstring('101', NULL)`, `bitstring(NULL::BIT, 4)` | `NULL` | | `bitstring('101', 3)` | `'101'` | | `bitstring('0', 1)` | `'0'` | | `bitstring('101', '8')` (length as a string literal) | `'00000101'` | | `bitstring('101', 2)` or `bitstring('101', 0)` | Error: `Length must be equal or larger than input string` | | `bitstring('101', -1)` | Error: `The bitstring length cannot be negative` | | `bitstring('', 4)` | Error: `Cannot cast empty string to BIT` | | `bitstring('102', 4)` | Error: `Invalid character encountered in string -> bit conversion: '2'` | | `bitstring('101', 2.5)` | Error: `No function matches the given name and argument types 'bitstring(STRING_LITERAL, 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-bitstring#set-up-the-examples): ``` run("SELECT bitstring(NULL, 20), bitstring('101', NULL), bitstring(NULL::BIT, 4)") run("SELECT CAST(bitstring('101', 3) AS VARCHAR), CAST(bitstring('0', 1) AS VARCHAR), " "CAST(bitstring('101', '8') AS VARCHAR)") run("SELECT bitstring('101', 2)") run("SELECT bitstring('101', -1)") run("SELECT bitstring('', 4)") run("SELECT bitstring('102', 4)") run("SELECT bitstring('101', 2.5)") ``` ``` [(None, None, None)] [('101', '0', '00000101')] OSError: Length must be equal or larger than input string OSError: The bitstring length cannot be negative OSError: Cannot cast empty string to BIT OSError: Invalid character encountered in string -> bit conversion: '2' InternalError: Binder Error: No function matches the given name and argument types 'bitstring(STRING_LITERAL, DECIMAL(2,1))'. You might need to add explicit type casts. ``` ## Examples Pad each stored string to 8 bits. The `VARCHAR` column and its cast to `BIT` give the same result: ``` run(f"SELECT id, bits, CAST(bitstring(bits, 8) AS VARCHAR), CAST(bitstring(CAST(bits AS BIT), 8) AS VARCHAR) " f"FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '1011', '00001011', '00001011'), (2, '0', '00000000', '00000000'), (3, None, None, None), (4, '10000000', '10000000', '10000000'), (5, '0110', '00000110', '00000110')] ``` Pad, then combine with a mask of the same length: ``` run(f"SELECT id, CAST(bitstring(bits, 8) & '00001111'::BIT AS VARCHAR) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '00001011'), (2, '00000000'), (3, None), (4, '00000000'), (5, '00000110')] ``` ## 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 `bitstring()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `bitstring()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `bitstring()` and keeps the rows that match. No rows are skipped in storage. The plan of a filter on `bitstring()` shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE bitstring(bits, 8) = '00001011'::BIT") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (bitstring(bits, 8) = │ │ 00001011) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ bits │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store the padded form.** If you filter on bit strings of one length, pad them when you write the rows. A comparison of the raw column with a constant, such as `bits = '00001011'`, is pushed down to VAST DataBase, so rows that don't match never leave storage. The plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE bits = '00001011'") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Combine it with a pushed-down condition.** In `id > 100 AND bitstring(bits, 8) = '00001011'::BIT`, `id > 100` is still evaluated in VAST DataBase, so `bitstring()` runs only on the rows that pass it. ## Limitations and errors - **The length can't be shorter than the input.** A bit string longer than `length` fails the query with `Length must be equal or larger than input string`. Choose a `length` at least as long as the longest value. - **Only 0s and 1s.** Any other character in `bits` fails with `Invalid character encountered in string -> bit conversion`, and an empty string with `Cannot cast empty string to BIT`. - **Two arguments, of the right types.** A number, `BLOB`, date, boolean or list as `bits`, a decimal `length`, or a call with one argument fails with `No function matches the given name and argument types`. The error lists the forms `bitstring` accepts: `bitstring(VARCHAR, INTEGER)` and `bitstring(BIT, INTEGER)`. ``` run("SELECT bitstring(101, 8)") run("SELECT bitstring('101')") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'bitstring(INTEGER_LITERAL, INTEGER_LITERAL)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'bitstring(STRING_LITERAL)'. You might need to add explicit type casts. ``` ## Similar functions | Function | Result for 5 or `'101'` | | --- | --- | | `bitstring('101', 8)` | `'00000101'`: padded to the length you choose | | `CAST('101' AS BIT)` | `'101'`: the bits as written ([BIT values and casts](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bit-values)) | | `CAST(5 AS BIT)` | `'00000000000000000000000000000101'`: the 32 bits of an `INTEGER` | | [bin](/develop/docs/dev-database-reference-sql-functions-numeric-bin): `bin(5)` | `'101'`, a `VARCHAR` without leading zeros | ``` run("SELECT CAST(bitstring('101', 8) AS VARCHAR), CAST('101'::BIT AS VARCHAR), CAST(CAST(5 AS BIT) AS VARCHAR), bin(5)") ``` ``` [('00000101', '101', '00000000000000000000000000000101', '101')] ``` 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) and [bitwise operators on BIT values](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bitwise-operators-on-bit). - [Where filters run](/develop/docs/dev-database-reference-sql-select#where-filters-run) and [pushdowns](/develop/docs/dev-database-reference-pushdowns).