--- title: "get_bit" slug: "dev-database-reference-sql-functions-binary-hash-uuid-get-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-get-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. # get_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 the bit at a given index of a bit string, as the `INTEGER` `0` or `1`. Index 0 is the leftmost bit: `get_bit('101101'::BIT, 1)` is `0`. ## Syntax ``` get_bit(bits, index) ``` | Argument | Type | Description | | --- | --- | --- | | `bits` | `BIT` | The bit string to read. | | `index` | `INTEGER` | The index of the bit, from 0 for the leftmost bit to `length(bits) - 1`. | **Returns:** `INTEGER` (`0` or `1`). ## 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_get_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_get_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 `get_bit` returns one bit of a bit string. Bits are indexed from 0 at the left, so for an integer cast to `BIT`, index 0 is the most significant bit and the last index is the least significant one: `get_bit(CAST(42 AS BIT), 31)` is `0`, because 42 is even. An index outside `0` to `length(bits) - 1` is an error. A string literal of 0s and 1s is cast to `BIT`, so `get_bit('101101', 0)` works. A `VARCHAR` column must be cast: `CAST(bits AS BIT)`. ## NULLs and edge cases | Input | Result | | --- | --- | | `get_bit(NULL, 0)`, `get_bit('101'::BIT, NULL)` | `NULL` | | `get_bit('101101'::BIT, 0)`, `get_bit('101101'::BIT, 5)` | `1`, `1` | | `get_bit('101101'::BIT, '1')` (index as a string literal) | `0` | | `get_bit('101101'::BIT, 6)` | Error: `bit index 6 out of valid range (0..5)` | | `get_bit('101101'::BIT, -1)` | Error: `bit index -1 out of valid range (0..5)` | | `get_bit('101101'::BIT, 1.6)` | Error: `No function matches the given name and argument types 'get_bit(BIT, 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-get-bit#set-up-the-examples): ``` run("SELECT get_bit(NULL, 0), get_bit('101'::BIT, NULL), get_bit('101101'::BIT, 0), get_bit('101101'::BIT, 5), " "get_bit('101101'::BIT, '1'), get_bit(CAST(42 AS BIT), 31)") run("SELECT get_bit('101101'::BIT, 6)") run("SELECT get_bit('101101'::BIT, -1)") run("SELECT get_bit('101101'::BIT, 1.6)") ``` ``` [(None, None, 1, 1, 0, 0)] OSError: bit index 6 out of valid range (0..5) OSError: bit index -1 out of valid range (0..5) InternalError: Binder Error: No function matches the given name and argument types 'get_bit(BIT, DECIMAL(2,1))'. You might need to add explicit type casts. ``` ## Examples The first flag of each row: ``` run(f"SELECT id, bits, get_bit(CAST(bits AS BIT), 0) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '1011', 1), (2, '0', 0), (3, None, None), (4, '10000000', 1), (5, '0110', 0)] ``` Keep the rows whose first flag is set: ``` run(f"SELECT id, bits FROM {TABLE} WHERE get_bit(CAST(bits AS BIT), 0) = 1 ORDER BY id LIMIT 10") ``` ``` [(1, '1011'), (4, '10000000')] ``` ## 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 `get_bit()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `get_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 `get_bit()` 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 get_bit(CAST(bits AS BIT), 0) = 1") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (get_bit(CAST(bits AS BIT)│ │ , 0) = 1) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ bits │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **A prefix test isn't faster.** `bits LIKE '1%'` finds the same rows from the `VARCHAR` column, but it runs in a `FILTER` step too: ``` plan(f"SELECT id FROM {TABLE} WHERE bits LIKE '1%'") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ prefix(bits, '1') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ bits │ │ id │ │ │ └───────────────────────────┘ ``` - **Store a flag you filter on often in its own column.** A `BOOLEAN` or integer column compared with a constant is pushed down to VAST DataBase, so rows that don't match never leave storage. - **Combine it with a pushed-down condition.** In `id > 100 AND get_bit(CAST(bits AS BIT), 0) = 1`, `id > 100` is still evaluated in VAST DataBase, so `get_bit()` runs only on the rows that pass it. ## Limitations and errors - **One short row fails the query.** An index past the end of any row's bit string fails the whole query with `bit index ... out of valid range`. Row 2 holds a single bit, so index 1 fails: ``` run(f"SELECT id, get_bit(CAST(bits AS BIT), 1) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` OSError: bit index 1 out of valid range (0..0) ``` 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 index must be an `INTEGER`.** An index computed with `length()`, which returns a `BIGINT`, fails with `No function matches the given name and argument types 'get_bit(BIT, BIGINT)'`. Cast it: `get_bit(b, CAST(length(b) - 1 AS INTEGER))`. ``` run("SELECT get_bit('1011'::BIT, length('1011'::BIT) - 1)") run("SELECT get_bit('1011'::BIT, CAST(length('1011'::BIT) - 1 AS INTEGER))") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'get_bit(BIT, BIGINT)'. You might need to add explicit type casts. [(1,)] ``` - **Bit strings only.** A number, `BLOB`, date, boolean, list or `VARCHAR` column fails with `No function matches the given name and argument types`. The error lists the one form `get_bit` accepts: `get_bit(BIT, INTEGER)`. ## Similar functions | Function | Result for `'101101'::BIT` | | --- | --- | | `get_bit(bits, 1)`: one bit, indexed from 0 | `0` | | [set_bit](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-set-bit): a copy with one bit changed, same indexes | `set_bit(bits, 1, 1)` is `'111101'` | | [bit_position](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bit-position): where a pattern starts, counted from 1 | `bit_position('1'::BIT, bits)` is `1` | | [bit_count](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-bit-count): how many 1s | `4` | ``` run("SELECT get_bit('101101'::BIT, 1), CAST(set_bit('101101'::BIT, 1, 1) AS VARCHAR), " "bit_position('1'::BIT, '101101'::BIT), bit_count('101101'::BIT)") ``` ``` [(0, '111101', 1, 4)] ``` 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).