dayofweek

Applies to VAST Cluster 5.5.

Functions › Date and time functions › Weeks and days of the week. Returns the day of the week of a date or timestamp, from 0 for Sunday to 6 for Saturday. weekday is the same function.

Syntax

dayofweek(value)
weekday(value)

Returns: BIGINT.

Aliases: weekday.

Same as: date_part('dow', value), also written date_part('dayofweek', value) or date_part('weekday', value); see date_part.

Set up the examples

The examples connect with the ADBC driver, as in VAST Query Engine (ADBC), and work in a schema called docs_sql_fn_date_time_dayofweek. Set QE_ENDPOINT, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and VASTDB_BUCKET (SQL reference), 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_dayofweek"'

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

dayofweek numbers the days of the week from Sunday:

To number the days from Monday (1) to Sunday (7), as ISO 8601 does, use isodow. For the day's name, use dayname.

NULLs and edge cases

The same cases, as the cluster returns them. They use the table and helpers from Set up the examples:

run(f"SELECT id, dayofweek(ts) FROM {TABLE} WHERE id = 4")
run("SELECT dayofweek(DATE '2026-03-01'), dayofweek(DATE '2026-03-02'), dayofweek(DATE '2026-02-28'), "
    "weekday(DATE '2026-03-01')")
run("SELECT dayofweek(DATE 'infinity'), dayofweek(TIMESTAMP '-infinity'), dayofweek(DATE '0001-01-01'), "
    "dayofweek(DATE '9999-12-31'), dayofweek(TIMESTAMP '1969-12-31 23:59:59.999999')")
run("SELECT dayofweek(NULL)")
run("SELECT dayofweek(INTERVAL '1 year 2 months 3 days')")
run("SELECT dayofweek(TIME '13:45:30')")
run("SELECT dayofweek('2026-03-01')")
run("SELECT dayofweek(123)")

[(4, None)]
[(0, 1, 6, 0)]
[(None, None, 1, 5, 3)]
InternalError: Binder Error: Could not choose a best candidate function for the function call "dayofweek("NULL")". In order to select one, please add explicit type casts.
OSError: interval units "dow" not recognized
InternalError: Binder Error: No function matches the given name and argument types 'dayofweek(TIME)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "dayofweek(STRING_LITERAL)". In order to select one, please add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'dayofweek(INTEGER_LITERAL)'. You might need to add explicit type casts.

Examples

The day of the week of each event, with its name:

run(f"SELECT id, d, dayofweek(d), weekday(ts), dayname(d) FROM {TABLE} ORDER BY id LIMIT 10")

[(1, datetime.date(2026, 2, 28), 6, 6, 'Saturday'), (2, datetime.date(2026, 3, 1), 0, 0, 'Sunday'), (3, datetime.date(2024, 12, 30), 1, 1, 'Monday'), (4, None, None, None, None), (5, datetime.date(2024, 2, 29), 4, 4, 'Thursday'), (6, datetime.date(1969, 12, 31), 3, 3, 'Wednesday'), (7, datetime.date(2027, 1, 3), 0, 0, 'Sunday')]

Keep only the events on a weekend (Sunday is 0, Saturday is 6):

run(f"SELECT id FROM {TABLE} WHERE dayofweek(d) IN (0, 6) ORDER BY id LIMIT 10")

[(1,), (2,), (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 dayofweek() is always computed by the Query Engine:

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

The plan of the weekend example shows the FILTER step above the scan:

plan(f"SELECT id FROM {TABLE} WHERE dayofweek(d) IN (0, 6)")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│  ((dayofweek(d) = 0) OR   │
│    (dayofweek(d) = 6))    │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘

Make it faster

• Store the day of the week if you filter on it often. Weekends recur every week, so no single range of dates selects them. Compute dayofweek when you write the rows and keep it in its own column: a comparison of that column with a constant is pushed down to VAST DataBase, dayofweek(d) IN (0, 6) isn't.
• Narrow the dates first. In d >= DATE '2026-01-01' AND dayofweek(d) IN (0, 6), the range on d is still evaluated in VAST DataBase, so dayofweek() runs only on the rows that pass it.

Limitations and errors

• No time-zone support. On a TIMESTAMP WITH TIME ZONE value, such as now(), dayofweek fails with an Extension Autoloading Error. Cast the value to TIMESTAMP first; see time zones.
• Not for TIME or INTERVAL. The error for an INTERVAL lists dayofweek(INTERVAL) among the candidates, but running it fails with interval units "dow" not recognized.
• TIMESTAMP_NS before 1970. Row 6's TIMESTAMP_NS value 1969-12-31 23:59:59.999999999 gives 4 (Thursday), while the TIMESTAMP value 1969-12-31 23:59:59.999999 gives 3 (Wednesday). If you need the day of nanosecond values before 1970 that are close to midnight, check the result or store the value as TIMESTAMP.
• Other SQL dialects' names aren't available. day_of_week and dow fail with Scalar Function with name ... does not exist!. Use dayofweek, or isodow for the ISO numbering.

run(f"SELECT id, dayofweek(tns), dayofweek(ts) FROM {TABLE} WHERE id = 6")
run("SELECT day_of_week(DATE '2026-03-01')")
run("SELECT dow(DATE '2026-03-01')")

[(6, 4, 3)]
InternalError: Catalog Error: Scalar Function with name day_of_week does not exist!
InternalError: Catalog Error: Scalar Function with name dow does not exist!

Similar functions

run("SELECT dayofweek(DATE '2026-03-01'), isodow(DATE '2026-03-01'), dayname(DATE '2026-03-01'), "
    "strftime(DATE '2026-03-01', '%w'), date_part('dow', DATE '2026-03-01')")

[(0, 7, 'Sunday', '0', 0)]

Clean up:

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

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See also

• isodow and dayname: other ways to get the day of the week.
• Date and time functions: all the date and time functions.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.