--- title: "hash" slug: "dev-database-reference-sql-functions-binary-hash-uuid-hash" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-hash" --- > ## 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. # hash *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) › Hashes.* Returns a 64-bit hash of one or more values of any type, as an unsigned `UBIGINT`. Use it to spread rows into buckets or to take a repeatable sample. It isn't a cryptographic digest: for that, use [sha256](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-sha256). ## Syntax ``` hash(x [, ...]) ``` | Argument | Type | Description | | --- | --- | --- | | `x, ...` | any | One or more values. Each argument changes the result, and so does their order. | **Returns:** `UBIGINT`, an unsigned 64-bit 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_hash`. 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 six events. Rows 1 and 3 have the same user and count, rows 2 and 5 have `0.0` and `-0.0` as their amount, and 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_hash"' 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}.events" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, user_name VARCHAR, n INTEGER, amount DOUBLE)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'ada', 42, 42.0), " "(2, 'grace', 7, 0.0), " "(3, 'ada', 42, 1.5), " "(4, 'linus', 1, 2.5), " "(5, 'grace', 9, '-0.0'::DOUBLE), " "(6, NULL, NULL, NULL)") ``` ``` [] [] [(6,)] ``` ## What it does `hash(x, ...)` combines its arguments into one 64-bit value. The same arguments always give the same value, and different arguments almost always give different values, so `hash(key) % n` spreads rows evenly over `n` buckets. - **Equal values hash equally across integer types.** `hash(42)`, `hash(42::TINYINT)` and `hash(42::BIGINT)` are equal, and so are a string and the same bytes as a `BLOB`. - **The type family matters.** `hash(42)` differs from `hash(42.0)` (a `DECIMAL`) and from `hash('42')`, and `hash(42::DOUBLE)` from `hash(42::FLOAT)`. Cast your keys to one type before you compare hashes. - **`0.0` and `-0.0` hash the same** as `DOUBLE`. - **Several arguments are hashed together, in order.** `hash('a', 'b')` differs from `hash('b', 'a')`, and `hash('hello', 1)` from `hash('hello')`. - **Any type works:** numbers, text, `BLOB`, `BOOLEAN`, dates, `UUID`, `BIT`, lists and structs. ## NULLs and edge cases | Input | Result | | --- | --- | | `hash(NULL) IS NULL` | `false`: NULL hashes to a fixed value | | `hash(NULL) = hash(NULL::VARCHAR)`, `hash(NULL) = hash(NULL::INTEGER)` | `true`, `true` | | `hash(NULL) = hash(NULL, NULL)` | `false` | | `hash(NULL, 1) IS NULL` | `false` | | `hash(42) = hash(42::BIGINT)`, `hash(42::TINYINT) = hash(42::BIGINT)` | `true`, `true` | | `hash(42) = hash(42.0)`, `hash(42) = hash('42')`, `hash(42::DOUBLE) = hash(42::FLOAT)` | `false`, `false`, `false` | | `hash(0.0::DOUBLE) = hash(-0.0::DOUBLE)` | `true` | | `hash('hello') = hash('hello'::BLOB)` | `true` | | `hash('a', 'b') = hash('b', 'a')`, `hash('hello') = hash('hello', 1)` | `false`, `false` | | `hash(true)`, `hash(DATE '2026-10-16')`, `hash([1, 2, 3])`, `hash({'a': 1})`, `hash('nan'::DOUBLE)` | a `UBIGINT` value each | | `typeof(hash('a'))` | `'UBIGINT'` | | `hash()` | Error: `No function matches the given name and argument types 'hash()'` | 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-hash#set-up-the-examples): ``` run("SELECT hash(NULL) IS NULL, hash(NULL) = hash(NULL::VARCHAR), hash(NULL) = hash(NULL::INTEGER), " "hash(NULL) = hash(NULL, NULL), hash(NULL, 1) IS NULL") run("SELECT hash(42) = hash(42::BIGINT), hash(42::TINYINT) = hash(42::BIGINT), hash(42) = hash(42.0), " "hash(42) = hash('42'), hash(42::DOUBLE) = hash(42::FLOAT), hash(0.0::DOUBLE) = hash(-0.0::DOUBLE)") run("SELECT hash('hello') = hash('hello'::BLOB), hash('a', 'b') = hash('b', 'a'), hash('hello') = hash('hello', 1)") run("SELECT typeof(hash(true)), typeof(hash(DATE '2026-10-16')), typeof(hash([1, 2, 3])), " "typeof(hash({'a': 1})), typeof(hash('nan'::DOUBLE)), typeof(hash('a'))") run("SELECT hash()") ``` ``` [(False, True, True, False, False)] [(True, True, False, False, False, True)] [(True, False, False)] [('UBIGINT', 'UBIGINT', 'UBIGINT', 'UBIGINT', 'UBIGINT', 'UBIGINT')] InternalError: Binder Error: No function matches the given name and argument types 'hash()'. You might need to add explicit type casts. ``` ## Examples Put each user in one of four buckets. Rows with the same user land in the same bucket, and so does the NULL row on every run: ``` run(f"SELECT id, user_name, hash(user_name) % 4 AS bucket FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 'ada', 3), (2, 'grace', 2), (3, 'ada', 3), (4, 'linus', 1), (5, 'grace', 2), (6, None, 1)] ``` Hash a key made of two columns, and compare hashes of the same number stored as an integer and as a `DOUBLE`. Rows 1 and 3 have the same key; `n` and `amount` hold 42 in row 1, but as different types, so their hashes differ. In row 6 both are NULL, which hash alike: ``` run(f"SELECT id, hash(user_name, n) = hash('ada', 42), hash(n) = hash(amount) FROM {TABLE} ORDER BY id LIMIT 10") run(f"SELECT id, hash(amount) = hash(0.0::DOUBLE) FROM {TABLE} WHERE id IN (2, 5) ORDER BY id LIMIT 10") ``` ``` [(1, True, False), (2, False, False), (3, True, False), (4, False, False), (5, False, False), (6, False, True)] [(2, True), (5, True)] ``` Take a repeatable sample of about half of the rows, and count how many fall in it. The same rows are chosen every time the query runs: ``` run(f"SELECT id FROM {TABLE} WHERE hash(id) % 2 = 0 ORDER BY id LIMIT 10") run(f"SELECT count(*), sum(CASE WHEN hash(id) % 2 = 0 THEN 1 ELSE 0 END) FROM {TABLE}") ``` ``` [(1,), (2,), (3,), (4,), (5,)] [(6, Decimal('5'))] ``` ## 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 `hash()` of a column is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the columns and the Query Engine hashes them for each row it returns. - **In `WHERE`,** the scan sends the columns for every row, and a `FILTER` step in the Query Engine hashes each row and keeps the ones that match. A sample by `hash(id) % 2 = 0` still reads the whole table. The plan of the sampling query shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE hash(id) % 2 = 0") ``` ``` ┌───────────────────────────┐ │ FILTER │ │ ──────────────────── │ │ ((hash(id) % 2) = 0) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store the bucket if you filter on it often.** Compute `hash(key) % n` when you write the rows and keep it in its own column: `bucket = 3` is pushed down, `hash(key) % 4 = 3` isn't. ## Limitations and errors - **Not a digest to share.** Don't compare the values with hashes computed by another system; use [sha256](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-sha256) for a digest that any system reproduces. - **Not for security.** It's a fast hash for spreading values, not a cryptographic one. - **No `GROUP BY` on a bucket.** `GROUP BY hash(id) % 2` fails with `The operator 'HASH_GROUP_BY' type=9 is currently not supported.` Count one bucket at a time with `sum(CASE WHEN ... THEN 1 ELSE 0 END)`, as in the sampling example. - **At least one argument.** `hash()` fails with `No function matches the given name and argument types 'hash()'`. - **Other hash names aren't available.** `xxhash64`, `murmurhash3_32` and `fnv_hash` fail with `Scalar Function with name ... does not exist!`. ``` run(f"SELECT hash(id) % 2 AS bucket, count(*) FROM {TABLE} GROUP BY hash(id) % 2 ORDER BY bucket LIMIT 10") run("SELECT xxhash64('a')") ``` ``` InternalError: The operator 'HASH_GROUP_BY' type=9 is currently not supported. InternalError: Catalog Error: Scalar Function with name xxhash64 does not exist! ``` ## Similar functions | Function | Takes | Returns | | --- | --- | --- | | `hash` | one or more values of any type | `UBIGINT` | | [md5](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-md5) | one `VARCHAR` or `BLOB` | `VARCHAR`, 32 hex digits | | [md5_number](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-md5-number) | one `VARCHAR` or `BLOB` | `HUGEINT` | | [sha1](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-sha1) | one `VARCHAR` or `BLOB` | `VARCHAR`, 40 hex digits | | [sha256](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-sha256) | one `VARCHAR` or `BLOB` | `VARCHAR`, 64 hex digits | ``` run("SELECT typeof(hash('a', 1)), typeof(md5('a')), typeof(md5_number('a')), typeof(sha1('a')), typeof(sha256('a'))") ``` ``` [('UBIGINT', 'VARCHAR', 'HUGEINT', 'VARCHAR', 'VARCHAR')] ``` 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 hash functions. - [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.