--- title: "setseed" slug: "dev-database-reference-sql-functions-numeric-setseed" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-setseed" --- > ## 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. # setseed *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric) › Random numbers.* Takes a seed, a number from -1 to 1, and returns NULL. A seed outside that range is an error. Setting a seed doesn't make the values of [random](/develop/docs/dev-database-reference-sql-functions-numeric-random) repeat. ## Syntax ``` setseed(x) ``` | Argument | Type | Description | | --- | --- | --- | | `x` | `DOUBLE` (any number, or a string that converts to one) | The seed. It must be from -1 to 1, both included. | **Returns:** NULL. `typeof(setseed(0.5))` is `"NULL"`; the driver returns the column as a 32-bit integer column holding NULLs. ## 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_numeric_setseed`. 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 four seeds. The last row has no seed: ``` 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_numeric_setseed"' 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}.seeds" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, seed DOUBLE)") run(f"INSERT INTO {TABLE} VALUES (1, 0.5), (2, -0.5), (3, 1.0), (4, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `setseed(x)` checks that `x` is from -1 to 1 and returns NULL; there's nothing else in its result. A string is converted to a `DOUBLE` first, so `setseed('0.5')` works. A seed outside the range, or NaN, fails the query. Setting the same seed twice doesn't give the same `random()` values, whether `random()` runs in the next statement or in the same one: see the block in [Examples](/develop/docs/dev-database-reference-sql-functions-numeric-setseed#examples). For a random sample that's the same on every run, see [random: make it faster](/develop/docs/dev-database-reference-sql-functions-numeric-random#make-it-faster). ## NULLs and edge cases | Input | Result | | --- | --- | | `setseed(NULL)` | `NULL` | | `setseed(0.5)`, `setseed(0)`, `setseed(1)`, `setseed(-1)` | `NULL` | | `setseed('0.5')` | `NULL`: the string is converted to `0.5` | | `setseed(2)`, `setseed(1.0000001)`, `setseed(-1.5)`, `setseed('nan'::DOUBLE)` | Error: `SETSEED accepts seed values between -1.0 and 1.0, inclusive` | | `setseed('abc')` | Error: `Could not convert string 'abc' to DOUBLE` | | `setseed(true)` | Error: `No function matches the given name and argument types 'setseed(BOOLEAN)'` | | `setseed()` | Error: `No function matches the given name and argument types 'setseed()'` | 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-numeric-setseed#set-up-the-examples): ``` run("SELECT setseed(NULL), setseed(0.5), setseed(0), setseed(1), setseed(-1), setseed('0.5')") run("SELECT setseed(2)") run("SELECT setseed(1.0000001)") run("SELECT setseed(-1.5)") run("SELECT setseed('nan'::DOUBLE)") run(f"SELECT setseed('abc') FROM {TABLE} LIMIT 1") run("SELECT setseed(true)") run("SELECT setseed()") ``` ``` [(None, None, None, None, None, None)] OSError: SETSEED accepts seed values between -1.0 and 1.0, inclusive OSError: SETSEED accepts seed values between -1.0 and 1.0, inclusive OSError: SETSEED accepts seed values between -1.0 and 1.0, inclusive OSError: SETSEED accepts seed values between -1.0 and 1.0, inclusive OSError: Could not convert string 'abc' to DOUBLE InternalError: Binder Error: No function matches the given name and argument types 'setseed(BOOLEAN)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'setseed()'. You might need to add explicit type casts. ``` ## Examples On a table, `setseed()` returns NULL for every row, so a condition such as `setseed(seed) IS NOT NULL` keeps no rows: ``` run(f"SELECT id, setseed(seed) FROM {TABLE} ORDER BY id LIMIT 10") run(f"SELECT id FROM {TABLE} WHERE setseed(seed) IS NOT NULL ORDER BY id LIMIT 10") ``` ``` [(1, None), (2, None), (3, None), (4, None)] [] ``` A seed doesn't repeat `random()`. The first check sets the seed in one statement and reads `random()` in the next; the second does both in one statement. Each compares two runs with the same seed, and prints `False` because they gave different values: ``` def random_after_seed(seed): with conn.cursor() as cur: cur.execute(f"SELECT setseed({seed})") cur.fetchall() cur.execute("SELECT random()") return cur.fetchall()[0][-1] def random_with_seed(seed): with conn.cursor() as cur: cur.execute(f"SELECT setseed({seed}), random()") return cur.fetchall()[0][-1] print(random_after_seed(0.5) == random_after_seed(0.5)) print(random_with_seed(0.5) == random_with_seed(0.5)) ``` ``` False False ``` ## 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`). `setseed()` is always computed by the Query Engine: the scan reads the column you pass, and the Query Engine calls `setseed()` for each row and casts its NULL result to `INTEGER`. The plan shows both steps: ``` plan(f"SELECT setseed(seed) FROM {TABLE}") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ CAST(setseed(seed) AS │ │ INTEGER) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: seed │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Call it on its own, not on a table.** `SELECT setseed(0.5)` reads no table. `SELECT setseed(seed) FROM seeds` reads the column and returns a NULL for every row. - **Don't filter on it.** `setseed()` is always NULL, so a condition on it either keeps no rows or every row, after a `FILTER` step that reads the whole column. ## Limitations and errors - **A seed from -1 to 1 only.** A larger or smaller number, or NaN, fails with `SETSEED accepts seed values between -1.0 and 1.0, inclusive`. To use a whole-number seed such as `42`, scale it into the range first, for example `setseed(42 / 100)`. - **One argument.** `setseed()` and `setseed(0.5, 1)` fail with `No function matches the given name and argument types`. A `BOOLEAN`, `DATE`, `INTERVAL`, `BLOB` or list fails the same way. - **A string must be a number.** `setseed('abc')` fails with `Could not convert string 'abc' to DOUBLE`. - **A seed doesn't make `random()` repeatable.** Two runs after the same seed give different values, as the block in [Examples](/develop/docs/dev-database-reference-sql-functions-numeric-setseed#examples) shows. For a sample that's the same on every run, store the random values in a column; see [random: make it faster](/develop/docs/dev-database-reference-sql-functions-numeric-random#make-it-faster). ``` run("SELECT setseed(0.5, 1)") run("SELECT setseed(42 / 100)") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'setseed(DECIMAL(2,1), INTEGER_LITERAL)'. You might need to add explicit type casts. [(None,)] ``` ## Similar functions | Function | Returns | | --- | --- | | `setseed(x)` | NULL; it checks a seed from -1 to 1 | | [random](/develop/docs/dev-database-reference-sql-functions-numeric-random) `()` | A random `DOUBLE` from 0 up to, not including, 1 | ``` run("SELECT setseed(0.5), random() >= 0") ``` ``` [(None, True)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric): all the numeric functions. - [random](/develop/docs/dev-database-reference-sql-functions-numeric-random). - [EXPLAIN](/develop/docs/dev-database-reference-sql-explain): how to read a plan.