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

> ## 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.

# trunc

*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.* Drops the fractional part of a number, so it rounds towards zero: down for a positive number, up for a negative one. An integer comes back unchanged, in its own type.

## Syntax

```
trunc(x)
```

| Argument | Type | Description |
| --- | --- | --- |
| `x` | any number: the signed and unsigned integer types, `DECIMAL`, `FLOAT` or `DOUBLE` | The value to truncate. |

**Returns:** the type of `x` for an integer, `FLOAT` or `DOUBLE`; `DECIMAL(p, 0)` for a `DECIMAL(p, s)`.

## 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_trunc`. 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`) and a count (`BIGINT`). Row 3 holds a count above 2^53, 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_numeric_trunc"'

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}.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), n BIGINT)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, 2.5, 2.45, 12), "
    "(2, -1.25, -1.35, -18), "
    "(3, -0.5, 99999999.99, 9007199254740993), "
    "(4, NULL, NULL, NULL)")
```

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

## What it does

`trunc(x)` cuts off everything after the decimal point: `trunc(2.7)` is 2 and `trunc(-2.7)` is -2. For a positive number that's the same as [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor); for a negative number it's the same as [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil).

The result keeps the type of `x`:

- **Integers:** the value comes back unchanged, in the same type. `trunc(9007199254740993::BIGINT)` is the `BIGINT` 9007199254740993, with no loss of precision. (`ceil`, `floor` and `round` turn an integer into a `DOUBLE`.)
- **`DECIMAL`:** the result is a `DECIMAL` with the same precision and no decimal places: `trunc(2.45::DECIMAL(10,2))` is a `DECIMAL(10,0)`. A number literal such as `2.7` is a `DECIMAL`.
- **`DOUBLE` and `FLOAT`:** the result has the same type and is a whole number, such as `2.0`. Truncating a value between -1 and 0 gives a negative zero, `-0.0`. `nan`, `inf` and `-inf` stay as they are.

## NULLs and edge cases

| Input | Result |
| --- | --- |
| `x` is NULL | `NULL` |
| `trunc(2.7)`, `trunc(-2.7)` | `2`, `-2` (`DECIMAL(2,0)`) |
| `trunc(-0.5)` | `0` (`DECIMAL`) |
| `trunc(-0.5::DOUBLE)` | `-0.0` |
| `trunc(5e-324::DOUBLE)`, the smallest positive `DOUBLE` | `0.0` |
| `trunc(&apos;nan&apos;::DOUBLE)`, `trunc(&apos;-inf&apos;::DOUBLE)` | `nan`, `-inf` |
| `trunc(9007199254740993::BIGINT)` | `9007199254740993`, a `BIGINT` |
| `trunc(2.45, 1)`: a number of places | Error: `No function matches the given name and argument types &apos;trunc(DECIMAL(3,2), INTEGER_LITERAL)&apos;` |
| A string, even `&apos;12&apos;` | Error: `Could not choose a best candidate function for the function call &quot;trunc(STRING_LITERAL)&quot;` |
| 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-trunc#set-up-the-examples):

```
run("SELECT trunc(NULL), trunc(2.7), trunc(-2.7), trunc(-0.5), typeof(trunc(2.45::DECIMAL(10,2)))")
run("SELECT trunc(-0.5::DOUBLE), signbit(trunc(-0.5::DOUBLE)), trunc(5e-324::DOUBLE), trunc('nan'::DOUBLE), "
    "trunc('-inf'::DOUBLE)")
run("SELECT trunc(9007199254740993::BIGINT), typeof(trunc(9007199254740993::BIGINT)), typeof(trunc(5::INTEGER))")
run("SELECT trunc(2.45, 1)")
run("SELECT trunc('12')")
```

```
[(None, Decimal('2'), Decimal('-2'), Decimal('0'), 'DECIMAL(10,0)')]
[(-0.0, True, 0.0, nan, -inf)]
[(9007199254740993, 'BIGINT', 'INTEGER')]
InternalError: Binder Error: No function matches the given name and argument types 'trunc(DECIMAL(3,2), INTEGER_LITERAL)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "trunc(STRING_LITERAL)". In order to select one, please add explicit type casts.
```

## Examples

Truncate each column. The `BIGINT` count keeps its type and its exact value:

```
run(f"SELECT id, trunc(x), trunc(price), trunc(n), floor(n) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 2.0, Decimal('2'), 12, 12.0), (2, -1.0, Decimal('-1'), -18, -18.0), (3, -0.0, Decimal('99999999'), 9007199254740993, 9007199254740992.0), (4, None, None, None, None)]
```

Cut a value to one decimal place, or two. `trunc` has no places argument, so scale, truncate and scale back; the result is a `DOUBLE`:

```
run(f"SELECT id, x, trunc(x * 10) / 10 FROM {TABLE} ORDER BY id LIMIT 10")
run("SELECT trunc(2.789 * 100) / 100, trunc(-2.789 * 100) / 100")
```

```
[(1, 2.5, 2.5), (2, -1.25, -1.2), (3, -0.5, -0.5), (4, None, None)]
[(2.78, -2.78)]
```

Keep the readings whose whole part is 2:

```
run(f"SELECT id, x FROM {TABLE} WHERE trunc(x) = 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 `trunc()` is always computed by the Query Engine:

- **In the `SELECT` list,** the scan reads the column and the Query Engine computes `trunc()` for each row it returns.
- **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `trunc()` 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 trunc(x) = 2")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│      (trunc(x) = 2.0)     │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         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, `trunc(x) = 2` is the same as `x &gt;= 2 AND x &lt; 3`, 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 AND x < 3")
```

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

- **A function of constants is fine.** It's computed once, before the scan: a condition such as `x &gt; round(2.4) + sqrt(0.25)` is still a column compared with a constant, and is pushed down.

## Limitations and errors

- **No number of places.** `trunc(x, n)` fails with `No function matches the given name and argument types`, also with a negative `n`. Use `trunc(x * 100) / 100` for two places, and so on; see [Examples](/develop/docs/dev-database-reference-sql-functions-numeric-trunc#examples). To round to `n` places instead, use [round](/develop/docs/dev-database-reference-sql-functions-numeric-round)`(x, n)`.
- **No `truncate`.** It fails with `Scalar Function with name truncate does not exist!`. Use `trunc`.
- **Strings aren't converted.** `trunc(&apos;12&apos;)` 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 truncate a date or timestamp, use [date_trunc](/develop/docs/dev-database-reference-sql-functions-date-time-date-trunc).

```
run("SELECT trunc(2.789, 2)")
run("SELECT truncate(2.789, 2)")
run("SELECT trunc(2.789 * 100) / 100, round(2.789, 2)")
```

```
InternalError: Binder Error: No function matches the given name and argument types 'trunc(DECIMAL(4,3), INTEGER_LITERAL)'. You might need to add explicit type casts.
InternalError: Catalog Error: Scalar Function with name truncate does not exist!
[(2.78, Decimal('2.79'))]
```

## Similar functions

| Function | Rounds | `2.5` | `-2.5` | `2.45` | `-0.5` |
| --- | --- | --- | --- | --- | --- |
| `trunc(x)` | towards zero | `2` | `-2` | `2` | `0` |
| [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor) | down, towards negative infinity | `2` | `-3` | `2` | `-1` |
| [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil) | up, towards positive infinity | `3` | `-2` | `3` | `0` |
| [round](/develop/docs/dev-database-reference-sql-functions-numeric-round) | to the nearest; halves away from zero | `3` | `-3` | `2` | `-1` |
| [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` |
| [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` |

`trunc`, `floor`, `ceil` and `round` return a `DECIMAL` for these `DECIMAL` literals; `round_even` and `even` return a `DOUBLE`:

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

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

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.
- [floor](/develop/docs/dev-database-reference-sql-functions-numeric-floor), [ceil](/develop/docs/dev-database-reference-sql-functions-numeric-ceil), [round](/develop/docs/dev-database-reference-sql-functions-numeric-round) and [date_trunc](/develop/docs/dev-database-reference-sql-functions-date-time-date-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.