--- title: "set_bit" slug: "dev-database-reference-sql-functions-binary-hash-uuid-set-bit" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-set-bit" --- > ## 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. # set_bit *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 copy of a bit string with the bit at one index set to `0` or `1`. Index 0 is the leftmost bit: `set_bit('101101'::BIT, 1, 1)` is `'111101'`. ## Syntax ``` set_bit(bits, index, new_value) ``` | Argument | Type | Description | | --- | --- | --- | | `bits` | `BIT` | The bit string to copy. | | `index` | `INTEGER` | The index of the bit to set, from 0 for the leftmost bit to `length(bits) - 1`. | | `new_value` | `INTEGER` | `0` or `1`. | **Returns:** `BIT`, the same length as `bits`. ## 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_set_bit`. 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. 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_set_bit"' 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 `set_bit` returns `bits` with the bit at `index` replaced by `new_value`. If the bit already has that value, the result is the same as the input. The input isn't changed: `set_bit` returns a new value. The result is a `BIT` value, which the client receives as bytes in an internal encoding, so cast it to `VARCHAR` to read it. A string literal of 0s and 1s is cast to `BIT`, so `set_bit('101101', 1, 1)` works; a `VARCHAR` column must be cast: `CAST(bits AS BIT)`. ## NULLs and edge cases | Input | Result | | --- | --- | | `set_bit(NULL, 0, 1)`, `set_bit('101'::BIT, NULL, 1)`, `set_bit('101'::BIT, 0, NULL)` | `NULL` | | `set_bit('101101'::BIT, 0, 0)` | `'001101'` | | `set_bit('101101'::BIT, 0, 1)` (already 1) | `'101101'` | | `set_bit('101101'::BIT, 1, 2)` or `new_value` `-1` | Error: `The new bit must be 1 or 0` | | `set_bit('101101'::BIT, 6, 1)` | Error: `bit index 6 out of valid range (0..5)` | | `set_bit('101101'::BIT, 1, true)` | Error: `No function matches the given name and argument types 'set_bit(BIT, INTEGER_LITERAL, BOOLEAN)'` | 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-set-bit#set-up-the-examples): ``` run("SELECT set_bit(NULL, 0, 1), set_bit('101'::BIT, NULL, 1), set_bit('101'::BIT, 0, NULL), " "CAST(set_bit('101101'::BIT, 0, 0) AS VARCHAR), CAST(set_bit('101101'::BIT, 0, 1) AS VARCHAR)") run("SELECT set_bit('101101'::BIT, 1, 2)") run("SELECT set_bit('101101'::BIT, 6, 1)") run("SELECT set_bit('101101'::BIT, 1, true)") ``` ``` [(None, None, None, '001101', '101101')] OSError: The new bit must be 1 or 0 OSError: bit index 6 out of valid range (0..5) InternalError: Binder Error: No function matches the given name and argument types 'set_bit(BIT, INTEGER_LITERAL, BOOLEAN)'. You might need to add explicit type casts. ``` ## Examples Turn on the first flag of each row. Rows 1 and 4 already have it: ``` run(f"SELECT id, bits, CAST(set_bit(CAST(bits AS BIT), 0, 1) AS VARCHAR) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '1011', '1011'), (2, '0', '1'), (3, None, None), (4, '10000000', '10000000'), (5, '0110', '1110')] ``` What the client receives without the cast to `VARCHAR`: ``` run("SELECT set_bit('101101'::BIT, 1, 1), CAST(set_bit('101101'::BIT, 1, 1) AS VARCHAR)") ``` ``` [(b'\x02\xfd', '111101')] ``` ## 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 `set_bit()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `set_bit()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `set_bit()` and keeps the rows that match. No rows are skipped in storage. The plan of a filter on `set_bit()` shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE CAST(set_bit(CAST(bits AS BIT), 0, 1) AS VARCHAR) = '1011'") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (CAST(set_bit(CAST(bits AS│ │ BIT), 0, 1) AS VARCHAR) =│ │ '1011') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ bits │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Filter with pushed-down conditions first.** `set_bit()` in the `SELECT` list runs only on the rows the scan returns, so a condition on a raw column compared with a constant, such as `id > 100`, cuts the work: it's evaluated in VAST DataBase. The plan for such a condition has no `FILTER` step: ``` plan(f"SELECT CAST(set_bit(CAST(bits AS BIT), 0, 1) AS VARCHAR) FROM {TABLE} WHERE id > 3") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ CAST(set_bit(CAST(bits AS │ │ BIT), 0, 1) AS VARCHAR) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: bits │ │ │ └───────────────────────────┘ ``` ## Limitations and errors - **An index past the end fails the query.** An index outside the bit string fails the statement with `bit index ... out of valid range`. Bring the values to one length first, with [bitstring](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bitstring), or store bit strings of one length. - **The new value is an integer 0 or 1.** Any other integer fails with `The new bit must be 1 or 0`, and a boolean fails with `No function matches the given name and argument types`. - **Bit strings only.** A number, `BLOB`, date, boolean, list or `VARCHAR` column as `bits` fails with `No function matches the given name and argument types`. The error lists the one form `set_bit` accepts: `set_bit(BIT, INTEGER, INTEGER)`. ``` run(f"SELECT set_bit(bits, 0, 1) FROM {TABLE} LIMIT 1") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'set_bit(VARCHAR, INTEGER_LITERAL, INTEGER_LITERAL)'. You might need to add explicit type casts. ``` ## Similar functions | Function | Result for `'1100'::BIT` | | --- | --- | | `set_bit(bits, 3, 1)`: set one bit | `'1101'` | | [get_bit](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-get-bit): read one bit, same indexes | `get_bit(bits, 3)` is `0` | | [OR](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bitwise-operators-on-bit) with a mask: set several bits | with the mask `'0011'::BIT`: `'1111'` | | [AND](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bitwise-operators-on-bit) with a mask: clear several bits | with the mask `'0111'::BIT`: `'0100'` | ``` run("SELECT CAST(set_bit('1100'::BIT, 3, 1) AS VARCHAR), get_bit('1100'::BIT, 3), " "CAST('1100'::BIT | '0011'::BIT AS VARCHAR), CAST('1100'::BIT & '0111'::BIT AS VARCHAR)") ``` ``` [('1101', 0, '1111', '0100')] ``` 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).