---
title: "isoyear"
slug: "dev-database-reference-sql-functions-date-time-isoyear"
updated: 2026-10-30T18:19:01Z
published: 2026-10-30T18:19:01Z
canonical: "docs.vastdata.com/dev-database-reference-sql-functions-date-time-isoyear"
---

> ## 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.

# isoyear

*Applies to VAST Cluster 5.5.*

*[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Date and time functions](/develop/docs/dev-database-reference-sql-functions-date-time) › Weeks and days of the week.* Returns the ISO 8601 year of a date or timestamp: the year that its ISO week belongs to. Near New Year it can differ from the calendar year.

## Syntax

```
isoyear(value)
```

| Argument | Type | Description |
| --- | --- | --- |
| `value` | `DATE` or `TIMESTAMP` (also `TIMESTAMP_NS`, `TIMESTAMP_MS`, `TIMESTAMP_S`) | The value to take the ISO year of. |

**Returns:** `BIGINT`.

**Same as:** `date_part('isoyear', value)`; see [date_part](/develop/docs/dev-database-reference-sql-functions-date-time-date-part).

## 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_date_time_isoyear`. 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 seven events. Each has a date (`d`), a timestamp (`ts`), a time of day (`t`) and a timestamp with nanoseconds (`tns`). Row 4 has no values, row 6 is the last moment of 1969, and row 7 is a Sunday early in January 2027:

```
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_date_time_isoyear"'

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}.events"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, d DATE, ts TIMESTAMP, t TIME, tns TIMESTAMP_NS)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, DATE '2026-02-28', TIMESTAMP '2026-02-28 23:15:00', TIME '23:15:00', "
    "CAST('2026-02-28 23:15:00.123456789' AS TIMESTAMP_NS)), "
    "(2, DATE '2026-03-01', TIMESTAMP '2026-03-01 08:30:45.123456', TIME '08:30:45.123456', "
    "CAST('2026-03-01 08:30:45.123456' AS TIMESTAMP_NS)), "
    "(3, DATE '2024-12-30', TIMESTAMP '2024-12-30 12:00:00', TIME '12:00:00', "
    "CAST('2024-12-30 12:00:00' AS TIMESTAMP_NS)), "
    "(4, NULL, NULL, NULL, NULL), "
    "(5, DATE '2024-02-29', TIMESTAMP '2024-02-29 00:00:00', TIME '00:00:00', "
    "CAST('2024-02-29 00:00:00' AS TIMESTAMP_NS)), "
    "(6, DATE '1969-12-31', TIMESTAMP '1969-12-31 23:59:59.999999', TIME '23:59:59.999999', "
    "CAST('1969-12-31 23:59:59.999999999' AS TIMESTAMP_NS)), "
    "(7, DATE '2027-01-03', TIMESTAMP '2027-01-03 00:00:00.5', TIME '00:00:00.000001', "
    "CAST('2027-01-03 00:00:00.5' AS TIMESTAMP_NS))")
```

```
[]
[]
[(7,)]
```

## What it does

ISO 8601 weeks start on Monday, and week 1 of a year is the week that holds the year's first Thursday. Every day belongs to exactly one ISO week, and `isoyear` returns the year of that week. For most of the year it's the calendar year; in the first and last days of a year it can be one more or one less:

| Date | Day | `year` | `isoyear` | Why |
| --- | --- | --- | --- | --- |
| `DATE &apos;2024-12-30&apos;` | Monday | `2024` | `2025` | Its week holds 2 January 2025, a Thursday: week 1 of 2025. |
| `DATE &apos;2021-01-01&apos;` | Friday | `2021` | `2020` | Its week started on Monday 28 December 2020: week 53 of 2020. |
| `DATE &apos;2027-01-03&apos;` | Sunday | `2027` | `2026` | The last day of week 53 of 2026. |
| `DATE &apos;2027-01-04&apos;` | Monday | `2027` | `2027` | The first day of week 1 of 2027. |

Use `isoyear` together with [week](/develop/docs/dev-database-reference-sql-functions-date-time-week), which is the ISO week number: `week` alone can't tell week 1 of 2025 from week 1 of 2024. [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek) gives both as one number.

## NULLs and edge cases

| Input | Result |
| --- | --- |
| A NULL value (row 4) | `NULL` |
| `DATE &apos;infinity&apos;`, `TIMESTAMP &apos;-infinity&apos;` | `NULL` |
| `DATE &apos;0001-01-01&apos;` | `1` |
| `DATE &apos;9999-12-31&apos;` | `9999` |
| `CAST(&apos;0044-03-15 (BC)&apos; AS DATE)` | `-43` |
| `TIMESTAMP &apos;1969-12-31 23:59:59.999999&apos;` | `1970` |
| An untyped `NULL`: `isoyear(NULL)` | Error: `Could not choose a best candidate function for the function call &quot;isoyear(&quot;NULL&quot;)&quot;` |
| An `INTERVAL` | Error: `interval units &quot;isoyear&quot; not recognized` |
| A `TIME` | Error: `No function matches the given name and argument types &apos;isoyear(TIME)&apos;` |
| A string | Error: `Could not choose a best candidate function`; cast it to `DATE` first |
| A number, boolean, `BLOB` or list | Error: `No function matches the given name and argument types`, for example `&apos;isoyear(INTEGER_LITERAL)&apos;` |

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-date-time-isoyear#set-up-the-examples):

```
run(f"SELECT id, isoyear(ts) FROM {TABLE} WHERE id = 4")
run("SELECT isoyear(DATE '2024-12-30'), isoyear(DATE '2021-01-01'), isoyear(DATE '2027-01-03'), "
    "isoyear(DATE '2027-01-04')")
run("SELECT isoyear(DATE 'infinity'), isoyear(TIMESTAMP '-infinity'), isoyear(DATE '0001-01-01'), "
    "isoyear(DATE '9999-12-31'), isoyear(CAST('0044-03-15 (BC)' AS DATE)), "
    "isoyear(TIMESTAMP '1969-12-31 23:59:59.999999')")
run("SELECT isoyear(NULL)")
run("SELECT isoyear(INTERVAL '1 year 2 months 3 days')")
run("SELECT isoyear(TIME '13:45:30')")
run("SELECT isoyear('2026-03-01')")
run("SELECT isoyear(123)")
```

```
[(4, None)]
[(2025, 2020, 2026, 2027)]
[(None, None, 1, 9999, -43, 1970)]
InternalError: Binder Error: Could not choose a best candidate function for the function call "isoyear("NULL")". In order to select one, please add explicit type casts.
OSError: interval units "isoyear" not recognized
InternalError: Binder Error: No function matches the given name and argument types 'isoyear(TIME)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "isoyear(STRING_LITERAL)". In order to select one, please add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'isoyear(INTEGER_LITERAL)'. You might need to add explicit type casts.
```

## Examples

The calendar year and the ISO year of each event. They differ for rows 3, 6 and 7:

```
run(f"SELECT id, d, year(d), isoyear(d) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, datetime.date(2026, 2, 28), 2026, 2026), (2, datetime.date(2026, 3, 1), 2026, 2026), (3, datetime.date(2024, 12, 30), 2024, 2025), (4, None, None, None), (5, datetime.date(2024, 2, 29), 2024, 2024), (6, datetime.date(1969, 12, 31), 1969, 1970), (7, datetime.date(2027, 1, 3), 2027, 2026)]
```

The ISO year and week of each event, for weekly reports:

```
run(f"SELECT id, isoyear(d), week(d) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, 2026, 9), (2, 2026, 9), (3, 2025, 1), (4, None, None), (5, 2024, 9), (6, 1970, 1), (7, 2026, 53)]
```

Keep only the events whose ISO year isn't their calendar year:

```
run(f"SELECT id FROM {TABLE} WHERE isoyear(d) <> year(d) ORDER BY id LIMIT 10")
```

```
[(3,), (6,), (7,)]
```

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

- **In the `SELECT` list,** the scan reads the column and the Query Engine computes `isoyear()` for each row it returns.
- **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `isoyear()` and keeps the rows that match. No rows are skipped in storage.

The plan of a filter on the ISO year shows the `FILTER` step above the scan:

```
plan(f"SELECT id FROM {TABLE} WHERE isoyear(d) = 2025")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│    (isoyear(d) = 2025)    │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘
```

## Make it faster

- **For one ISO year, filter on a range of the raw column.** ISO year 2025 runs from Monday 30 December 2024 to Sunday 28 December 2025, so `d &gt;= DATE &apos;2024-12-30&apos; AND d &lt; DATE &apos;2025-12-29&apos;` selects the same rows as `isoyear(d) = 2025`. The range is pushed down to VAST DataBase, so rows outside it never leave storage. The plan for the range has no `FILTER` step:

```
plan(f"SELECT id FROM {TABLE} WHERE d >= DATE '2024-12-30' AND d < DATE '2025-12-29'")
```

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

- **Store the ISO year if you filter on it often.** Compute it when you write the rows and keep it in its own column: `iso_year = 2025` is pushed down, `isoyear(d) = 2025` isn't.

## Limitations and errors

- **No time-zone support.** On a `TIMESTAMP WITH TIME ZONE` value, such as `now()`, `isoyear` fails with an `Extension Autoloading Error`. Cast the value to `TIMESTAMP` first; see [time zones](/develop/docs/dev-database-reference-sql-functions-date-time-time-zones).
- **Not for `TIME` or `INTERVAL`.** The error for an `INTERVAL` lists `isoyear(INTERVAL)` among the candidates, but running it fails with `interval units &quot;isoyear&quot; not recognized`. `date_part(&apos;isoyear&apos;, ...)` on a `TIME` fails with `&quot;time&quot; units &quot;isoyear&quot; not recognized`.

```
run("SELECT date_part('isoyear', TIME '13:45:30')")
```

```
OSError: "time" units "isoyear" not recognized
```

## Similar functions

| Function | Returns | Result for `DATE &apos;2024-12-30&apos;` (`isoyear` gives `2025`) |
| --- | --- | --- |
| [year](/develop/docs/dev-database-reference-sql-functions-date-time-year) | The calendar year | `2024` |
| [week](/develop/docs/dev-database-reference-sql-functions-date-time-week) | The ISO week, 1 to 53 | `1` |
| [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek) | The ISO year and week as one number | `202501` |
| [strftime](/develop/docs/dev-database-reference-sql-functions-date-time-strftime) with `&apos;%G&apos;` | The ISO year, as text | `&apos;2025&apos;` |
| [date_part](/develop/docs/dev-database-reference-sql-functions-date-time-date-part) with `&apos;isoyear&apos;` | The same as `isoyear` | `2025` |

```
run("SELECT isoyear(DATE '2024-12-30'), year(DATE '2024-12-30'), week(DATE '2024-12-30'), "
    "yearweek(DATE '2024-12-30'), strftime(DATE '2024-12-30', '%G'), date_part('isoyear', DATE '2024-12-30')")
```

```
[(2025, 2024, 1, 202501, '2025', 2025)]
```

Clean up:

```
run(f"DROP TABLE IF EXISTS {TABLE}")
run(f"DROP SCHEMA IF EXISTS {SCHEMA}")
conn.close()
```

```
[]
[]
```

## See also

- [week](/develop/docs/dev-database-reference-sql-functions-date-time-week) and [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek): the ISO week.
- [Date and time functions](/develop/docs/dev-database-reference-sql-functions-date-time): all the date and time functions.
- [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.