--- title: "from_hex" slug: "dev-database-reference-sql-functions-binary-hash-uuid-from-hex" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-from-hex" --- > ## 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. # from_hex *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) › Binary data and encodings.* Reads a string of hexadecimal digits and returns the bytes it describes, as a `BLOB`. `unhex` is the same function. It's the reverse of [hex](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-hex). ## Syntax ``` from_hex(s) unhex(s) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | Hexadecimal digits, `0` to `9` and `A` to `F` in either case, with nothing else in the string. | **Returns:** `BLOB`. **Aliases:** `unhex`. ## 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_from_hex`. 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 codes: each has a hex string and a `BLOB`. The last 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_from_hex"' 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}.codes" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, hx VARCHAR, data BLOB)") run(f"INSERT INTO {TABLE} VALUES " "(1, '68656C6C6F', '\\x25\\x50\\x44\\x46'::BLOB), " "(2, '', ''::BLOB), " "(3, '00ff', '\\x00\\xFF'::BLOB), " "(4, 'ABC', '\\x61'::BLOB), " "(5, NULL, NULL)") ``` ``` [] [] [(5,)] ``` ## What it does `from_hex` reads the string two digits at a time and makes one byte of each pair: `from_hex('68656C6C6F')` gives the five bytes of `hello`. Upper-case and lower-case digits give the same bytes. **An odd number of digits:** the first digit makes a byte on its own, and the rest are read in pairs. `from_hex('a')` gives the byte `0x0A`, and `from_hex('abc')` gives `0x0A 0xBC`. Pad the string with a leading `0` if you meant something else. **Bytes, not text.** The result is a `BLOB`, which Python shows as `bytes` (`b'hello'`). To read bytes that hold UTF-8 text as a `VARCHAR`, apply [decode](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-decode): `decode(from_hex('C3A9'))` gives `'é'`. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `''` (empty string) | `b''` (empty bytes) | | `'68656c6c6f'` (lower case) | `b'hello'` | | `'a'` (one digit) | `b'\n'` (the byte `0x0A`) | | `'abc'` (three digits) | `b'\n\xbc'` | | `from_hex(hex('hello')) = 'hello'::BLOB` | `true` | | `'0x41'`, `'41 42'`, `'zz'` | Error: `Invalid input for hex digit: ...`, naming the first character that isn't a hex digit | | A number, `BLOB`, date, boolean or list | Error: `No function matches the given name and argument types` | The same cases, as the cluster returns them. They use the helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-from-hex#set-up-the-examples): ``` run("SELECT from_hex(NULL), from_hex(''), from_hex('68656c6c6f'), from_hex('a'), from_hex('abc')") run("SELECT from_hex(hex('hello')) = 'hello'::BLOB, decode(from_hex('C3A9')) = '\u00e9'") run("SELECT from_hex('0x41')") run("SELECT from_hex('zz')") run("SELECT from_hex(123)") ``` ``` [(None, b'', b'hello', b'\n', b'\n\xbc')] [(True, True)] OSError: Invalid input for hex digit: x OSError: Invalid input for hex digit: z InternalError: Binder Error: No function matches the given name and argument types 'from_hex(INTEGER_LITERAL)'. You might need to add explicit type casts. ``` ## Examples Each code's hex string as bytes. `unhex` gives the same results: ``` run(f"SELECT id, hx, from_hex(hx), unhex(hx) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '68656C6C6F', b'hello', b'hello'), (2, '', b'', b''), (3, '00ff', b'\x00\xff', b'\x00\xff'), (4, 'ABC', b'\n\xbc', b'\n\xbc'), (5, None, None, None)] ``` Find a `BLOB` by its hex form. The constant is turned into bytes once, and compared with the column: ``` run(f"SELECT id FROM {TABLE} WHERE data = from_hex('25504446') ORDER BY id LIMIT 10") ``` ``` [(1,)] ``` ## 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`). `from_hex()` is computed by the Query Engine: - **On a column,** in the `SELECT` list the Query Engine computes `from_hex()` for each row the scan returns. In `WHERE`, the scan sends the column for every row, and a `FILTER` step computes `from_hex()` and keeps the rows that match. - **On a constant,** the Query Engine computes it once, before the scan. A comparison of a column with that constant, such as `data = from_hex('25504446')`, is then pushed down to VAST DataBase like any comparison with a constant. The plan of a filter on `from_hex()` of a column shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE from_hex(hx) IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (from_hex(hx) IS NOT NULL)│ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ hx │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Apply `from_hex` to the constant, not to the column.** If you store bytes, store them in a `BLOB` column and compare it with `from_hex('...')`. The plan of the second example has no `FILTER` step: VAST DataBase returns only the matching rows. ``` plan(f"SELECT id FROM {TABLE} WHERE data = from_hex('25504446')") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` ## Limitations and errors - **Only hex digits.** A `0x` prefix, a space or any other character fails the query with `Invalid input for hex digit:` and the character. One bad value in a column fails the whole query, not just its row: clean the strings first, for example with `replace()`. - **`VARCHAR` only.** A number, a `BLOB`, a date, a boolean or a list fails with `No function matches the given name and argument types`; the error lists `from_hex(VARCHAR) -> BLOB` as the only candidate. ``` run("SELECT from_hex('41 42')") run(f"SELECT id, from_hex(replace(hx, ' ', '')) FROM {TABLE} WHERE id = 1 LIMIT 10") ``` ``` OSError: Invalid input for hex digit: [(1, b'hello')] ``` ## Similar functions | Function | What it reads | Result for the bytes of `'hé'` | | --- | --- | --- | | `from_hex` | Hexadecimal text | `from_hex('68C3A9')` gives `b'h\xc3\xa9'` | | [hex](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-hex) | The reverse: bytes, a string or an integer to hex text | `hex(encode('hé'))` gives `'68C3A9'` | | [from_base64](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-from-base64) | Base64 text | `from_base64('aMOp')` gives the same bytes | | [encode](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-encode) | A `VARCHAR`, as its UTF-8 bytes | `encode('hé')` gives the same bytes | | [decode](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-decode) | A `BLOB` of UTF-8 bytes, back to a `VARCHAR` | `decode(from_hex('68C3A9'))` gives `'hé'` | ``` run("SELECT from_hex('68C3A9'), hex(encode('h\u00e9')), from_base64('aMOp'), encode('h\u00e9'), decode(from_hex('68C3A9'))") ``` ``` [(b'h\xc3\xa9', '68C3A9', b'h\xc3\xa9', b'h\xc3\xa9', 'hé')] ``` 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): all the functions in this family. - [Data types in SQL](/develop/docs/dev-database-reference-sql-data-types): `BLOB` columns. - [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.