---
title: "round_even"
slug: "dev-database-reference-sql-functions-numeric-round-even"
updated: 2026-10-30T18:18:51Z
published: 2026-10-30T18:18:51Z
canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-round-even"
---

> ## 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_even

*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) › Rounding.* Rounds a number to `n` decimal places, sending a value that is exactly halfway to the even digit (banker's rounding): `2.5` becomes `2` and `3.5` becomes `4`. `roundbankers` is the same function.

## Syntax

```
round_even(x, n)
roundbankers(x, n)
```

| Argument | Type | Description |
| --- | --- | --- |
| `x` | Any number: integer, `DECIMAL`, `FLOAT` or `DOUBLE` | The value to round. |
| `n` | An integer | The number of decimal places. A negative `n` rounds to tens, hundreds and so on. Both arguments are required. |

**Returns:** `DOUBLE`, also for an integer or `DECIMAL` `x`. A `FLOAT` `x` gives a `FLOAT`.

**Aliases:** `roundbankers`.

## 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_even`. 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 invoice lines with an amount in `DOUBLE` and a price in `DECIMAL(10,2)`. 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_even"'

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, "<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}.lines"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, amount DOUBLE, price DECIMAL(10,2))")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, 2.5, 2.50), "
    "(2, 3.5, -7.25), "
    "(3, -2.5, 12.35), "
    "(4, 0.125, 3.14), "
    "(5, NULL, NULL)")
```

```
[]
[]
[(5,)]
```

## What it does

`round_even(x, n)` rounds `x` to `n` decimal places. A value that isn't halfway between two results rounds to the nearer one, as with [round](/develop/docs/dev-database-reference-sql-functions-numeric-round). A value exactly halfway goes to the result whose last digit is even:

| Call | Result | `round` gives |
| --- | --- | --- |
| `round_even(2.5, 0)` | `2.0` | `3` |
| `round_even(3.5, 0)` | `4.0` |  |
| `round_even(-2.5, 0)` | `-2.0` | `-3` |
| `round_even(0.125, 2)` | `0.12` |  |
| `round_even(0.375, 2)` | `0.38` |  |
| `round_even(1250, -2)` | `1200.0` |  |
| `round_even(1350, -2)` | `1400.0` |  |

Over many values, halves round up as often as down, so totals of rounded values don't drift upwards.

A decimal value that has no exact binary form may not count as a half: `round_even(2.45, 1)` returns `2.5`, not `2.4`, and `round_even(2.55, 1)` returns `2.6`.

## NULLs and edge cases

| Input | Result |
| --- | --- |
| `x` or `n` is `NULL` | `NULL` |
| `-0.5` to 0 places | `-0.0` |
| `NaN`, `inf` | `nan`, `inf` |
| `2.45` and `2.55` to 1 place | `2.5` and `2.6` |
| `2.5` to 400 places | `2.5` |
| `2.5` to -400 places | `0.0` |
| `9223372036854775807` to -1 places | `9.223372036854776e+18` (a `DOUBLE`) |
| `2.5::FLOAT` | `2.0`, as a `FLOAT` |
| An integer or a `DECIMAL` | A `DOUBLE`: `typeof(round_even(2.5::DECIMAL(4,1), 0))` is `DOUBLE` |

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-even#set-up-the-examples):

```
run("SELECT round_even(NULL, 0), round_even(2.5, NULL), round_even(-0.5, 0)")
run("SELECT round_even('NaN'::DOUBLE, 0), round_even('inf'::DOUBLE, 0)")
run("SELECT round_even(2.45, 1), round_even(2.55, 1), round_even(2.5, 400), round_even(2.5, -400)")
run("SELECT round_even(9223372036854775807, -1), round_even(2.5::FLOAT, 0), round_even(25, 0)")
run("SELECT typeof(round_even(2.5, 0)), typeof(round_even(2.5::DECIMAL(4,1), 0)), typeof(round_even(2.5::FLOAT, 0))")
```

```
[(None, None, -0.0)]
[(nan, inf)]
[(2.5, 2.6, 2.5, 0.0)]
[(9.223372036854776e+18, 2.0, 25.0)]
[('DOUBLE', 'DOUBLE', 'FLOAT')]
```

## Examples

Each amount to a whole number and each price to one decimal place, with both names of the function. `-7.25` becomes `-7.2` and `12.35` becomes `12.4`, the even digit in each case:

```
run(f"SELECT id, round_even(amount, 0), roundbankers(amount, 0), round_even(price, 1) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 2.0, 2.0, 2.5), (2, 4.0, 4.0, -7.2), (3, -2.0, -2.0, 12.4), (4, 0.0, 0.0, 3.1), (5, None, None, None)]
```

The lines whose amount rounds to 2:

```
run(f"SELECT id, amount FROM {TABLE} WHERE round_even(amount, 0) = 2 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_even()` is always computed by the Query Engine:

- **In the `SELECT` list,** the scan reads the column and the Query Engine computes `round_even()` 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_even()` 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_even(amount, 0) = 2")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│ (CASE  WHEN ((((abs(amount│
│ ) * 10.0) % 10.0) = 5.0)) │
│  THEN ((round((amount / 2 │
│ .0), 0) * 2.0)) ELSE round│
│   (amount, 0) END = 2.0)  │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│           amount          │
│             id            │
│                           │
└───────────────────────────┘
```

## Make it faster

- **Filter on a range of the raw column instead.** `round_even(amount, 0) = 2` keeps the amounts from 1.5 to 2.5, both included; `amount &gt;= 1.5 AND amount &lt;= 2.5` returns the same rows, and a comparison of the raw column with a constant 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 amount >= 1.5 AND amount <= 2.5")
```

```
┌───────────────────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│      Projections: id      │
│                           │
└───────────────────────────┘
```

- **Round last.** Call `round_even()` in the `SELECT` list of the rows you return, and filter and sort on the unrounded column.

## Limitations and errors

- **Two arguments.** `round_even(2.5)` fails with `Macro function round_even(x, n) requires 2 positional arguments, but a single positional argument was provided.` Pass `0` for whole numbers.
- **`n` must be an integer.** `round_even(2.5, 1.7)` fails with `No function matches the given name and argument types &apos;round(DOUBLE, DECIMAL(2,1))&apos;`.
- **Numbers only.** A string, date, boolean, list or `BLOB` fails. The error names `abs()`, which `round_even` calls: for example `No function matches the given name and argument types &apos;abs(DATE)&apos;`.
- **The result is a `DOUBLE`,** even for a `DECIMAL`. Cast it back if you need a `DECIMAL`: `CAST(round_even(price, 1) AS DECIMAL(10,1))`.

```
run("SELECT round_even(2.5)")
run("SELECT round_even(2.5, 1.7)")
run(f"SELECT round_even(DATE '2026-10-16', 0) FROM {TABLE} LIMIT 1")
run(f"SELECT id, CAST(round_even(price, 1) AS DECIMAL(10,1)) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
InternalError: Binder Error: Macro function round_even(x, n) requires 2 positional arguments, but a single positional argument was provided.
InternalError: Binder Error: No function matches the given name and argument types 'round(DOUBLE, DECIMAL(2,1))'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'abs(DATE)'. You might need to add explicit type casts.
[(1, Decimal('2.5')), (2, Decimal('-7.2')), (3, Decimal('12.4')), (4, Decimal('3.1')), (5, None)]
```

## Similar functions

| Function | Halves | `2.5` | `-2.5` | `0.5` | Result type for a `DECIMAL` |
| --- | --- | --- | --- | --- | --- |
| `round_even(x, 0)`, also `roundbankers` | to the even digit | `2.0` | `-2.0` | `0.0` | `DOUBLE` |
| [round](/develop/docs/dev-database-reference-sql-functions-numeric-round) | away from zero | `3` | `-3` | `1` | `DECIMAL` |
| [even](/develop/docs/dev-database-reference-sql-functions-numeric-even) | rounds away from zero to an even integer | `4.0` | `-4.0` | `2.0` | `DOUBLE` |
| [trunc](/develop/docs/dev-database-reference-sql-functions-numeric-trunc) | drops the decimals | `2` | `-2` | `0` | `DECIMAL` |
| [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor) | rounds down | `2` | `-3` | `0` | `DECIMAL` |

```
run("SELECT round_even(2.5, 0), roundbankers(2.5, 0), round(2.5), even(2.5), trunc(2.5), floor(2.5)")
run("SELECT round_even(-2.5, 0), roundbankers(-2.5, 0), round(-2.5), even(-2.5), trunc(-2.5), floor(-2.5)")
run("SELECT round_even(0.5, 0), roundbankers(0.5, 0), round(0.5), even(0.5), trunc(0.5), floor(0.5)")
```

```
[(2.0, 2.0, Decimal('3'), 4.0, Decimal('2'), Decimal('2'))]
[(-2.0, -2.0, Decimal('-3'), -4.0, Decimal('-2'), Decimal('-3'))]
[(0.0, 0.0, Decimal('1'), 2.0, Decimal('0'), Decimal('0'))]
```

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](/develop/docs/dev-database-reference-sql-functions-numeric-round), [even](/develop/docs/dev-database-reference-sql-functions-numeric-even) 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.