--- title: "round" slug: "dev-database-reference-sql-functions-numeric-round" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-round" --- > ## 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. # round *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) › Sign and rounding.* Rounds a number to the nearest integer, or to `n` decimal places. Halves are rounded away from zero: 2.5 becomes 3 and -2.5 becomes -3. A negative `n` rounds to tens, hundreds and so on. ## Syntax ``` round(x) round(x, n) ``` | Argument | Type | Description | | --- | --- | --- | | `x` | `DECIMAL`, `FLOAT` or `DOUBLE`; an integer is converted to `DOUBLE` | The value to round. | | `n` | `INTEGER` | The number of decimal places to keep; `0` if you leave it out. A negative `n` rounds to the left of the decimal point: `-1` to tens, `-2` to hundreds. On a `DECIMAL`, `n` must be a constant. | **Returns:** for a `DECIMAL(p, s)`, a `DECIMAL(p, n)` when `n` is between 0 and `s`, `DECIMAL(p, s)` when `n` is larger than `s`, and `DECIMAL(p, 0)` without `n` or with a negative `n`. `FLOAT` for a `FLOAT`, and `DOUBLE` for a `DOUBLE` or an 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_numeric_round`. 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 measurements: a reading (`DOUBLE`), a price (`DECIMAL`), a number of places (`INTEGER`) and a count (`BIGINT`). 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_numeric_round"' 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}.measurements" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, x DOUBLE, price DECIMAL(10, 2), places INTEGER, n BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, 2.5, 2.45, 1, 1234), " "(2, -2.5, -1.35, 0, 15), " "(3, 1.005, 10.05, 2, 25), " "(4, NULL, NULL, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `round(x, n)` returns the value nearest to `x` that has at most `n` decimal places. When `x` is exactly halfway, it rounds away from zero, for `DECIMAL`, `DOUBLE` and `FLOAT` alike: `round(0.5)` is 1, `round(2.5)` is 3, `round(-0.5)` is -1 and `round(-2.5)` is -3. For halves that go to the even digit (banker's rounding), use [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even). | Call | Result | | --- | --- | | `round(2.45)` | `2` | | `round(2.55)` | `3` | | `round(2.345, 2)` | `2.35` | | `round(1234.5678, 0)` | `1235` | | `round(1234.5678, -2)` | `1200` | | `round(15, -1)`, `round(25, -1)`, `round(-25, -1)` | `20.0`, `30.0`, `-30.0` | ### The result type The result keeps the kind of number you pass in: - **`DECIMAL`:** the result is exact, and keeps the precision of `x`. `round(2.345, 2)` is the `DECIMAL(4,2)` 2.35, `round(1234.5678, -2)` is the `DECIMAL(8,0)` 1200, and `round(99999999.99::DECIMAL(10,2))` is the `DECIMAL(10,0)` 100000000. With more places than `x` has, `x` comes back unchanged: `round(2.5, 20)` is the `DECIMAL(2,1)` 2.5. A number literal such as `2.345` is a `DECIMAL`. - **`DOUBLE` and `FLOAT`:** the result has the same type. Rounding a value between -0.5 and 0 gives a negative zero: `round(-0.4::DOUBLE)` is `-0.0`. `nan`, `inf` and `-inf` stay as they are. - **Integers:** there's no integer form of `round`. An integer is converted to `DOUBLE`, and the result is a `DOUBLE`: `round(5::TINYINT)` is `5.0`, and `round(15, -1)` is `20.0`. Above 2^53 a `DOUBLE` can't hold every integer, so `round(9007199254740993::BIGINT)` returns `9007199254740992.0`. ### DECIMAL or DOUBLE A `DOUBLE` holds a binary fraction, so a decimal value such as 1.005 isn't stored exactly, and rounding it to two places doesn't always give what the decimal digits suggest: `round(1.005::DOUBLE, 2)` is `1.0`, while `round(1.005, 2)` on the `DECIMAL` literal is `1.01`. A `FLOAT` holds fewer digits still: `round(2.345::FLOAT, 2)` comes back as `2.3499999046325684`. When the decimal digits matter, as for money, store and round `DECIMAL` values. ## NULLs and edge cases | Input | Result | | --- | --- | | `x` is NULL | `NULL` | | `n` is NULL | `NULL` | | `round(0.5)`, `round(1.5)`, `round(2.5)` | `1`, `2`, `3` | | `round(-0.5)`, `round(-2.5)` | `-1`, `-3` | | `round(2.5::DOUBLE)`, `round(-2.5::DOUBLE)` | `3.0`, `-3.0` | | `round(1.005, 2)`, `round(1.005::DOUBLE, 2)` | `1.01`, `1.0` | | `round(2.5, 20)` | `2.5`, a `DECIMAL(2,1)` | | `round(2.5::DOUBLE, 400)`, `round(2.5::DOUBLE, -400)` | `2.5`, `0.0` | | `round(-0.4::DOUBLE)` | `-0.0` | | `round('nan'::DOUBLE, 2)`, `round('inf'::DOUBLE, 2)` | `nan`, `inf` | | `round(5::TINYINT)` | `5.0`, a `DOUBLE` | | `round(2.45, '1')`: `n` as a string | `2.5`: the string is converted | | `round(2.45, 1.6)`: `n` not an integer | Error: `No function matches the given name and argument types 'round(DECIMAL(3,2), DECIMAL(2,1))'` | | `round(2.5::DOUBLE, 2147483648)`: `n` too large for an `INTEGER` | Error: `No function matches the given name and argument types 'round(DOUBLE, INTEGER_LITERAL)'` | | `x` a string, even `'12'` | Error: `Could not choose a best candidate function for the function call "round(STRING_LITERAL)"` | | `x` a date, boolean, `BLOB`, list or interval | Error: `No function matches the given name and argument types` | 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-round#set-up-the-examples): ``` run("SELECT round(NULL), round(2.5, NULL), round(0.5), round(1.5), round(2.5), round(-0.5), round(-2.5)") run("SELECT round(2.5::DOUBLE), round(-2.5::DOUBLE), round(1.005, 2), round(1.005::DOUBLE, 2), " "round(2.5, 20), typeof(round(2.5, 20))") run("SELECT round(2.5::DOUBLE, 400), round(2.5::DOUBLE, -400), round(-0.4::DOUBLE), signbit(round(-0.4::DOUBLE)), " "round('nan'::DOUBLE, 2), round('inf'::DOUBLE, 2)") run("SELECT round(5::TINYINT), typeof(round(5::TINYINT)), round(2.45, '1')") run("SELECT round(2.45, 1.6)") run("SELECT round(2.5::DOUBLE, 2147483648)") run("SELECT round('12')") ``` ``` [(None, None, Decimal('1'), Decimal('2'), Decimal('3'), Decimal('-1'), Decimal('-3'))] [(3.0, -3.0, Decimal('1.01'), 1.0, Decimal('2.5'), 'DECIMAL(2,1)')] [(2.5, 0.0, -0.0, True, nan, inf)] [(5.0, 'DOUBLE', Decimal('2.5'))] InternalError: Binder Error: No function matches the given name and argument types 'round(DECIMAL(3,2), DECIMAL(2,1))'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'round(DOUBLE, INTEGER_LITERAL)'. You might need to add explicit type casts. InternalError: Binder Error: Could not choose a best candidate function for the function call "round(STRING_LITERAL)". In order to select one, please add explicit type casts. ``` ## Examples Round each reading and price to an integer and to one or two places. Row 3's reading, 1.005, rounds to `1.0` at two places, because the `DOUBLE` doesn't hold 1.005 exactly: ``` run(f"SELECT id, round(x), round(x, 2), round(price), round(price, 1) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 3.0, 2.5, Decimal('2'), Decimal('2.5')), (2, -3.0, -2.5, Decimal('-1'), Decimal('-1.4')), (3, 1.0, 1.0, Decimal('10'), Decimal('10.1')), (4, None, None, None, None)] ``` Round the counts to tens and hundreds. The `BIGINT` count comes back as a `DOUBLE`: ``` run(f"SELECT id, n, round(n, -1), round(n, -2) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 1234, 1230.0, 1200.0), (2, 15, 20.0, 0.0), (3, 25, 30.0, 0.0), (4, None, None, None)] ``` Keep the readings that round to 3: ``` run(f"SELECT id, x FROM {TABLE} WHERE round(x) = 3 ORDER BY id LIMIT 10") ``` ``` [(1, 2.5)] ``` ## 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 `round()` of a column is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `round()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `round()` 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 round(x) = 3") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (round(x) = 3.0) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ x │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Write the condition as a range on the raw column.** For a positive target, `round(x) = 3` is the same as `x >= 2.5 AND x < 3.5`, and that form is pushed down to VAST DataBase, so rows that don't match never leave storage. Its plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE x >= 2.5 AND x < 3.5") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **The same goes for decimal places.** `round(price, 1) = 2.5` runs in a `FILTER` step; `price >= 2.45 AND price < 2.55` is pushed down. - **`round()` of a constant is fine.** A function of constants is computed once, before the scan, so `x > round(2.4) + sqrt(0.25)` is still a column compared with a constant. Its plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE x > round(2.4) + sqrt(0.25)") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` ## Limitations and errors - **On a `DECIMAL`, the number of places must be a constant.** With a column, `round(price, places)` fails with `Not implemented Error: ROUND(DECIMAL, INTEGER) with non-constant precision is not supported`. Write the number of places in the query. - **`n` must be an integer.** `round(2.45, 1.6)` fails with `No function matches the given name and argument types`, and so does a value of `n` too large for an `INTEGER`. - **One rounding mode.** Halves always go away from zero; there's no third argument for the mode, and `round(2.5, 0, 'half_even')` fails with `No function matches the given name and argument types`. Use [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even) for banker's rounding. `round_half_up` doesn't exist. - **Integers become `DOUBLE`.** See [The result type](/develop/docs/dev-database-reference-sql-functions-numeric-round#the-result-type). Large `BIGINT` values can lose precision. - **Strings aren't converted for `x`.** `round('12')` fails with `Could not choose a best candidate function`. Cast the string to a number first. - **Numbers only.** A date, a boolean, a `BLOB`, a list or an interval fails with `No function matches the given name and argument types`. To round a date or timestamp, use [date_trunc](/develop/docs/dev-database-reference-sql-functions-date-time-date-trunc). ``` run(f"SELECT round(price, places) FROM {TABLE}") run("SELECT round(2.5, 0, 'half_even')") run("SELECT round(2.5, 0), round_even(2.5, 0)") ``` ``` InternalError: Not implemented Error: ROUND(DECIMAL, INTEGER) with non-constant precision is not supported InternalError: Binder Error: No function matches the given name and argument types 'round(DECIMAL(2,1), INTEGER_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. [(Decimal('3'), 2.0)] ``` ## Similar functions | Function | Rounds | `2.5` | `-2.5` | `2.45` | `-0.5` | | --- | --- | --- | --- | --- | --- | | `round(x)` | to the nearest; halves away from zero | `3` | `-3` | `2` | `-1` | | [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even) (also `roundbankers`) | to the nearest; halves to the even digit | `2.0` | `-2.0` | `2.0` | `-0.0` | | [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil) | up, towards positive infinity | `3` | `-2` | `3` | `0` | | [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor) | down, towards negative infinity | `2` | `-3` | `2` | `-1` | | [trunc](/develop/docs/dev-database-reference-sql-functions-numeric-trunc) | towards zero | `2` | `-2` | `2` | `0` | | [even](/develop/docs/dev-database-reference-sql-functions-numeric-even) | away from zero, to an even integer | `4.0` | `-4.0` | `4.0` | `-2.0` | `round`, `ceil`, `floor` and `trunc` return a `DECIMAL` for these `DECIMAL` literals; `round_even` and `even` return a `DOUBLE`. At one decimal place, `round(2.45, 1)` is `2.5` and `round(2.35, 1)` is `2.4`: ``` run("SELECT round(2.5), round_even(2.5, 0), ceil(2.5), floor(2.5), trunc(2.5), even(2.5)") run("SELECT round(-2.5), round_even(-2.5, 0), ceil(-2.5), floor(-2.5), trunc(-2.5), even(-2.5)") run("SELECT round(2.45), round_even(2.45, 0), ceil(2.45), floor(2.45), trunc(2.45), even(2.45)") run("SELECT round(-0.5), round_even(-0.5, 0), ceil(-0.5), floor(-0.5), trunc(-0.5), even(-0.5)") run("SELECT round(2.45, 1), round_even(2.45, 1), round(2.35, 1), round_even(2.35, 1)") ``` ``` [(Decimal('3'), 2.0, Decimal('3'), Decimal('2'), Decimal('2'), 4.0)] [(Decimal('-3'), -2.0, Decimal('-2'), Decimal('-3'), Decimal('-2'), -4.0)] [(Decimal('2'), 2.0, Decimal('3'), Decimal('2'), Decimal('2'), 4.0)] [(Decimal('-1'), -0.0, Decimal('0'), Decimal('-1'), Decimal('0'), -2.0)] [(Decimal('2.5'), 2.5, Decimal('2.4'), 2.4)] ``` 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. - [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even), [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil), [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor) and [trunc](/develop/docs/dev-database-reference-sql-functions-numeric-trunc). - [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.