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

# 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) › Sign and rounding.* Rounds a number away from zero to the next even integer: 2.5 becomes 4, 3 becomes 4 and -0.5 becomes -2. An even integer stays as it is. The result is a `DOUBLE`.

## Syntax

```
even(x)
```

| Argument | Type | Description |
| --- | --- | --- |
| `x` | `DOUBLE`; any other number, and a string that holds a number, is converted to `DOUBLE` | The value to round. |

**Returns:** `DOUBLE`.

## 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_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 four bookings: a number of guests (`INTEGER`), a length of stay in nights (`DOUBLE`) and a price (`DECIMAL`). 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_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}.bookings"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, guests INTEGER, nights DOUBLE, price DECIMAL(10, 2))")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, 3, 2.5, 2.45), "
    "(2, 2, 0.1, -1.35), "
    "(3, 7, -0.5, 10.00), "
    "(4, NULL, NULL, NULL)")
```

```
[]
[]
[(4,)]
```

## What it does

`even(x)` rounds `x` away from zero, to the nearest even integer that is at least as far from zero as `x`:

| Call | Result |
| --- | --- |
| `even(2)`, `even(0)` | `2.0`, `0.0`: already even |
| `even(1)`, `even(3.0)` | `2.0`, `4.0` |
| `even(0.1)`, `even(-0.1)` | `2.0`, `-2.0` |
| `even(2.5)`, `even(-2.5)` | `4.0`, `-4.0` |
| `even(-0.5)` | `-2.0` |

Any fraction moves the value to the next even integer, so `even(0.1)` is already 2. `even` isn't a rounding to the nearest: for halves that go to the even digit (banker's rounding), use [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even).

`even` has a single form, for `DOUBLE`, so every argument is converted to `DOUBLE` first and the result is always a `DOUBLE`: `even(2)` is `2.0`, and `even(2.45)` on a `DECIMAL` is the `DOUBLE` 4.0. Above 2^53 a `DOUBLE` can't hold every integer, so `even(9007199254740993::BIGINT)` returns `9007199254740992.0`. A string that holds a number is converted too: `even(&apos;12&apos;)` is `12.0`.

On special `DOUBLE` values, `nan`, `inf`, `-inf` and `-0.0` stay as they are, and the smallest positive `DOUBLE`, `5e-324`, becomes `2.0`.

## NULLs and edge cases

| Input | Result |
| --- | --- |
| `x` is NULL | `NULL` |
| `even(0)`, `even(-0.0::DOUBLE)` | `0.0`, `-0.0` |
| `even(5e-324::DOUBLE)` | `2.0` |
| `even(&apos;nan&apos;::DOUBLE)`, `even(&apos;inf&apos;::DOUBLE)` | `nan`, `inf` |
| `even(1.7976931348623157e308)`, the largest `DOUBLE` | unchanged |
| `even(9007199254740993::BIGINT)` | `9007199254740992.0` |
| `even(&apos;12&apos;)` | `12.0`: the string is converted |
| `even(&apos;abc&apos;)` | Error: `Could not convert string &apos;abc&apos; to DOUBLE` |
| `even(2.5, 1)`: a second argument | Error: `No function matches the given name and argument types &apos;even(DECIMAL(2,1), INTEGER_LITERAL)&apos;` |
| 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-even#set-up-the-examples):

```
run("SELECT even(NULL), even(0), even(-0.0::DOUBLE), signbit(even(-0.0::DOUBLE)), even(5e-324::DOUBLE)")
run("SELECT even('nan'::DOUBLE), even('inf'::DOUBLE), even(1.7976931348623157e308), even(9007199254740993::BIGINT)")
run("SELECT even(2), typeof(even(2)), even(2.45), typeof(even(2.45)), even('12')")
run("SELECT even('abc')")
run("SELECT even(2.5, 1)")
run("SELECT even(true)")
```

```
[(None, 0.0, -0.0, True, 2.0)]
[(nan, inf, 1.7976931348623157e+308, 9007199254740992.0)]
[(2.0, 'DOUBLE', 4.0, 'DOUBLE', 12.0)]
OSError: Could not convert string 'abc' to DOUBLE
InternalError: Binder Error: No function matches the given name and argument types 'even(DECIMAL(2,1), INTEGER_LITERAL)'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'even(BOOLEAN)'. You might need to add explicit type casts.
```

## Examples

Round each column to an even number. Each result is a `DOUBLE`, also for the `INTEGER` and `DECIMAL` columns:

```
run(f"SELECT id, even(guests), even(nights), even(price) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 4.0, 4.0, 4.0), (2, 2.0, 2.0, -2.0), (3, 8.0, -2.0, 10.0), (4, None, None, None)]
```

Seat guests at tables for two: the number of seats to set is the guest count rounded up to an even number, cast back to an integer:

```
run(f"SELECT id, guests, CAST(even(guests) AS INTEGER) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 3, 4), (2, 2, 2), (3, 7, 8), (4, None, None)]
```

Keep the bookings that need four seats:

```
run(f"SELECT id, guests FROM {TABLE} WHERE even(guests) = 4 ORDER BY id LIMIT 10")
```

```
[(1, 3)]
```

## 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 `even()` is always computed by the Query Engine:

- **In the `SELECT` list,** the scan reads the column and the Query Engine computes `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 `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 even(guests) = 4")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│    (even(CAST(guests AS   │
│       DOUBLE)) = 4.0)     │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│           guests          │
│             id            │
│                           │
└───────────────────────────┘
```

## Make it faster

- **Write the condition on the raw column.** For whole numbers, `even(guests) = 4` is the same as `guests &gt;= 3 AND guests &lt;= 4`, which compares the column with constants and 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 guests >= 3 AND guests <= 4")
```

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

- **Use `even()` in the `SELECT` list,** where it runs only on the rows the scan returns.

## Limitations and errors

- **Always a `DOUBLE`.** Cast the result back if you need an integer: `CAST(even(n) AS INTEGER)`. Large `BIGINT` values lose precision on the way; see [What it does](/develop/docs/dev-database-reference-sql-functions-numeric-even#what-it-does).
- **Not a rounding to the nearest.** `even(0.1)` is 2. For banker's rounding, use [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even); for the nearest integer, use [round](/develop/docs/dev-database-reference-sql-functions-numeric-round).
- **A string that isn't a number fails the query.** `even(&apos;abc&apos;)` fails with `Could not convert string &apos;abc&apos; to DOUBLE`.
- **One argument only.** There's no number of places: `even(2.5, 1)` fails with `No function matches the given name and argument types`.
- **Numbers only.** A date, a boolean, a `BLOB`, a list or an interval fails with `No function matches the given name and argument types`.

```
run("SELECT even(0.1), round(0.1), round_even(0.1, 0)")
run("SELECT CAST(even(3) AS INTEGER)")
```

```
[(2.0, Decimal('0'), 0.0)]
[(4,)]
```

## Similar functions

| Function | Rounds | `2.5` | `-2.5` | `2.45` | `-0.5` |
| --- | --- | --- | --- | --- | --- |
| `even(x)` | away from zero, to an even integer | `4.0` | `-4.0` | `4.0` | `-2.0` |
| [round_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even) | to the nearest; halves to the even digit | `2.0` | `-2.0` | `2.0` | `-0.0` |
| [round](/develop/docs/dev-database-reference-sql-functions-numeric-round) | to the nearest; halves away from zero | `3` | `-3` | `2` | `-1` |
| [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` and `round_even` return a `DOUBLE`; `round`, `ceil`, `floor` and `trunc` return a `DECIMAL` for these `DECIMAL` literals:

```
run("SELECT even(2.5), round_even(2.5, 0), round(2.5), ceil(2.5), floor(2.5), trunc(2.5)")
run("SELECT even(-2.5), round_even(-2.5, 0), round(-2.5), ceil(-2.5), floor(-2.5), trunc(-2.5)")
run("SELECT even(2.45), round_even(2.45, 0), round(2.45), ceil(2.45), floor(2.45), trunc(2.45)")
run("SELECT even(-0.5), round_even(-0.5, 0), round(-0.5), ceil(-0.5), floor(-0.5), trunc(-0.5)")
```

```
[(4.0, 2.0, Decimal('3'), Decimal('3'), Decimal('2'), Decimal('2'))]
[(-4.0, -2.0, Decimal('-3'), Decimal('-2'), Decimal('-3'), Decimal('-2'))]
[(4.0, 2.0, Decimal('2'), Decimal('3'), Decimal('2'), Decimal('2'))]
[(-2.0, -0.0, Decimal('-1'), Decimal('0'), Decimal('-1'), 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_even](/develop/docs/dev-database-reference-sql-functions-numeric-round-even), [round](/develop/docs/dev-database-reference-sql-functions-numeric-round) and [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil).
- [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.