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

> ## 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.

# week

*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 week number of a date or timestamp, from 1 to 53. ISO weeks start on Monday, and week 1 is the week that contains the year's first Thursday. `weekofyear` is the same function.

## Syntax

```
week(value)
weekofyear(value)
```

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

**Returns:** `BIGINT`.

**Aliases:** `weekofyear`.

**Same as:** `date_part('week', value)` and `extract(week FROM value)`; the part also has the names `w`, `weeks` and `weekofyear`. 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_week`. 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 six events. Each has a date (`d`) and a timestamp (`ts`). Rows 3, 5 and 6 are around New Year, where the ISO week and the calendar year disagree, and row 4 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_date_time_week"'

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)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, DATE '2026-02-28', TIMESTAMP '2026-02-28 23:15:00'), "
    "(2, DATE '2026-03-01', TIMESTAMP '2026-03-01 08:30:45'), "
    "(3, DATE '2024-12-30', TIMESTAMP '2024-12-30 12:00:00'), "
    "(4, NULL, NULL), "
    "(5, DATE '2027-01-03', TIMESTAMP '2027-01-03 00:00:00'), "
    "(6, DATE '2027-01-04', TIMESTAMP '2027-01-04 09:00:00')")
```

```
[]
[]
[(6,)]
```

## What it does

`week` returns the ISO 8601 week of a date or timestamp. ISO weeks run from Monday to Sunday, and week 1 of a year is the week that holds its first Thursday. So a year has 52 or 53 weeks, and the first and last days of a calendar year can belong to a week of the next or the previous year:

| Date | Day | `week` | ISO year ([isoyear](/develop/docs/dev-database-reference-sql-functions-date-time-isoyear)) | Calendar year ([year](/develop/docs/dev-database-reference-sql-functions-date-time-year)) |
| --- | --- | --- | --- | --- |
| `DATE &apos;2024-12-29&apos;` | Sunday | `52` | 2024 | 2024 |
| `DATE &apos;2024-12-30&apos;` | Monday | `1` | 2025 | 2024 |
| `DATE &apos;2021-01-01&apos;` | Friday | `53` | 2020 | 2021 |
| `DATE &apos;2027-01-03&apos;` | Sunday | `53` | 2026 | 2027 |
| `DATE &apos;2027-01-04&apos;` | Monday | `1` | 2027 | 2027 |

The same dates, as the cluster returns them:

```
for day in ["2024-12-29", "2024-12-30", "2021-01-01", "2027-01-03", "2027-01-04"]:
    run(f"SELECT DATE '{day}', dayname(DATE '{day}'), week(DATE '{day}'), isoyear(DATE '{day}'), year(DATE '{day}')")
```

```
[(datetime.date(2024, 12, 29), 'Sunday', 52, 2024, 2024)]
[(datetime.date(2024, 12, 30), 'Monday', 1, 2025, 2024)]
[(datetime.date(2021, 1, 1), 'Friday', 53, 2020, 2021)]
[(datetime.date(2027, 1, 3), 'Sunday', 53, 2026, 2027)]
[(datetime.date(2027, 1, 4), 'Monday', 1, 2027, 2027)]
```

`week` doesn't say which year the week belongs to. To label a week, use [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek), which gives `202501` for 30 December 2024, or `isoyear` with `week`, not `year` with `week`.

It works on every timestamp precision. `weekofyear` is the same function under another name.

## 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;` | `52` |
| `TIMESTAMP &apos;1969-12-31 23:59:59.999999&apos;` | `1` |
| An untyped `NULL`: `week(NULL)` | Error: `Could not choose a best candidate function for the function call &quot;week(&quot;NULL&quot;)&quot;` |
| An `INTERVAL` | Error: `interval units &quot;week&quot; not recognized` |
| A `TIME` | Error: `No function matches the given name and argument types &apos;week(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;week(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-week#set-up-the-examples):

```
run(f"SELECT id, week(d), weekofyear(ts) FROM {TABLE} WHERE id = 4")
run("SELECT week(DATE 'infinity'), week(TIMESTAMP '-infinity'), week(DATE '0001-01-01'), "
    "week(DATE '9999-12-31'), week(TIMESTAMP '1969-12-31 23:59:59.999999')")
run("SELECT week(DATE '2024-12-29'), week(DATE '2024-12-30'), week(DATE '2021-01-01'), "
    "week(DATE '2027-01-03'), week(DATE '2027-01-04'), weekofyear(DATE '2021-01-01')")
run("SELECT week(NULL)")
run("SELECT week(INTERVAL 1 DAY)")
run("SELECT week(TIME '13:45:30')")
run("SELECT week('2024-02-29')")
run("SELECT week(123)")
```

```
[(4, None, None)]
[(None, None, 1, 52, 1)]
[(52, 1, 53, 53, 1, 53)]
InternalError: Binder Error: Could not choose a best candidate function for the function call "week("NULL")". In order to select one, please add explicit type casts.
OSError: interval units "week" not recognized
InternalError: Binder Error: No function matches the given name and argument types 'week(TIME)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "week(STRING_LITERAL)". In order to select one, please add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'week(INTEGER_LITERAL)'. You might need to add explicit type casts.
```

## Examples

The week of each event, next to its calendar year and its ISO year and week. Row 3 is in week 1 of 2025, and row 5 in week 53 of 2026:

```
run(f"SELECT id, d, week(d), weekofyear(ts), year(d), yearweek(d) FROM {TABLE} ORDER BY id LIMIT 10")
```

```
[(1, datetime.date(2026, 2, 28), 9, 9, 2026, 202609), (2, datetime.date(2026, 3, 1), 9, 9, 2026, 202609), (3, datetime.date(2024, 12, 30), 1, 1, 2024, 202501), (4, None, None, None, None, None), (5, datetime.date(2027, 1, 3), 53, 53, 2027, 202653), (6, datetime.date(2027, 1, 4), 1, 1, 2027, 202701)]
```

Keep only the events in week 9. Without a year, this matches week 9 of every year. [Make it faster](/develop/docs/dev-database-reference-sql-functions-date-time-week#make-it-faster) has a faster way to write it for one year:

```
run(f"SELECT id FROM {TABLE} WHERE week(d) = 9 ORDER BY id LIMIT 10")
```

```
[(1,), (2,)]
```

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

- **In the `SELECT` list,** the scan reads the column and the Query Engine computes `week()` for each row it returns.
- **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `week()` 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 week(d) = 9")
```

```
┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│      ("week"(d) = 9)      │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘
```

## Make it faster

- **Filter on a range of the raw column for one week.** ISO week 9 of 2026 runs from Monday 23 February to Sunday 1 March 2026. [date_trunc](/develop/docs/dev-database-reference-sql-functions-date-time-date-trunc) with `&apos;week&apos;` gives the Monday: `date_trunc(&apos;week&apos;, DATE &apos;2026-03-01&apos;)` is `2026-02-23`. `d &gt;= DATE &apos;2026-02-23&apos; AND d &lt; DATE &apos;2026-03-02&apos;` is pushed down to VAST DataBase, so rows from other weeks never leave storage. The plan for the range has no `FILTER` step:

```
run("SELECT date_trunc('week', DATE '2026-03-01')")
run(f"SELECT id FROM {TABLE} WHERE d >= DATE '2026-02-23' AND d < DATE '2026-03-02' ORDER BY id LIMIT 10")
plan(f"SELECT id FROM {TABLE} WHERE d >= DATE '2026-02-23' AND d < DATE '2026-03-02'")
```

```
[(datetime.date(2026, 2, 23),)]
[(1,), (2,)]
┌───────────────────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│      Projections: id      │
│                           │
└───────────────────────────┘
```

- **Store the week if you filter on it often** and a range doesn't fit your query, for example week 9 of every year. Compute it with [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek) or `week` when you write the rows and keep it in its own column: `event_week = 9` is pushed down, `week(d) = 9` isn't.

## Limitations and errors

- **ISO weeks only.** `week` has no option for weeks that start on Sunday, or for week 1 starting on 1 January. For those numberings, use [strftime](/develop/docs/dev-database-reference-sql-functions-date-time-strftime) with `&apos;%U&apos;` (weeks starting on Sunday) or `&apos;%W&apos;` (weeks starting on Monday), which return text; see [Similar functions](/develop/docs/dev-database-reference-sql-functions-date-time-week#similar-functions).
- **Dates and timestamps only.** `week` of an `INTERVAL` fails with `interval units &quot;week&quot; not recognized`, although the error for a wrong argument lists `week(INTERVAL)`.
- **No time-zone support.** On a `TIMESTAMP WITH TIME ZONE` value, such as `now()`, `week` 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).
- **Other SQL dialects' names aren't available.** `week_of_year` fails with `Scalar Function with name week_of_year does not exist!`. Use `week` or `weekofyear`.

```
run("SELECT week_of_year(DATE '2026-03-01')")
```

```
InternalError: Catalog Error: Scalar Function with name week_of_year does not exist!
```

## Similar functions

| Function | Returns | Result for `TIMESTAMP &apos;2024-12-30 13:45:30.123456&apos;`, a Monday (`week` gives `1`) |
| --- | --- | --- |
| `weekofyear` | The same as `week` | `1` |
| [yearweek](/develop/docs/dev-database-reference-sql-functions-date-time-yearweek) | The ISO year and week as one number | `202501` |
| [isoyear](/develop/docs/dev-database-reference-sql-functions-date-time-isoyear) | The ISO year the week belongs to | `2025` |
| [year](/develop/docs/dev-database-reference-sql-functions-date-time-year) | The calendar year | `2024` |
| [strftime](/develop/docs/dev-database-reference-sql-functions-date-time-strftime) with `&apos;%V %G %U %W&apos;` | ISO week, ISO year, week from Sunday, week from Monday, as text | `&apos;01 2025 52 53&apos;` |
| [date_part](/develop/docs/dev-database-reference-sql-functions-date-time-date-part) with `&apos;week&apos;` | The same as `week` | `1` |

```
run("SELECT week(TIMESTAMP '2024-12-30 13:45:30.123456'), weekofyear(TIMESTAMP '2024-12-30 13:45:30.123456'), "
    "yearweek(TIMESTAMP '2024-12-30 13:45:30.123456'), isoyear(TIMESTAMP '2024-12-30 13:45:30.123456'), "
    "year(TIMESTAMP '2024-12-30 13:45:30.123456'), strftime(TIMESTAMP '2024-12-30 13:45:30.123456', '%V %G %U %W'), "
    "date_part('week', TIMESTAMP '2024-12-30 13:45:30.123456')")
```

```
[(1, 1, 202501, 2025, 2024, '01 2025 52 53', 1)]
```

Clean up:

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

```
[]
[]
```

## See also

- [dayofweek](/develop/docs/dev-database-reference-sql-functions-date-time-dayofweek) and [isodow](/develop/docs/dev-database-reference-sql-functions-date-time-isodow): the day of the 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.