dayname

Applies to VAST Cluster 5.5.

Functions › Date and time functions › Names and calendar. Returns the English name of the day of the week of a date or timestamp, such as Sunday.

Syntax

dayname(value)

Returns: VARCHAR.

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_dayname. 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_dayname"'

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

dayname returns the full English name of the day, starting with a capital letter: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday or Sunday. For example, dayname(DATE '2026-03-01') is 'Sunday' and dayname(DATE '2026-03-07') is 'Saturday'. It takes no language argument.

For the short name (Sun), use the %a code of strftime. For the day as a number, use dayofweek or isodow.

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

[(4, None)]
[(None, None, None)]
[('Monday', 'Friday', 'Friday', 'Wednesday')]
InternalError: Binder Error: No function matches the given name and argument types 'dayname(INTERVAL)'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'dayname(TIME)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "dayname(STRING_LITERAL)". In order to select one, please add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'dayname(INTEGER_LITERAL)'. You might need to add explicit type casts.

Examples

The name of the day of each event:

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

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

A readable date, such as Sunday 1 March 2026, built from dayname, day, monthname and year:

run(f"SELECT id, dayname(d) || ' ' || CAST(day(d) AS VARCHAR) || ' ' || monthname(d) || ' ' || "
    f"CAST(year(d) AS VARCHAR) FROM {TABLE} ORDER BY id LIMIT 10")

[(1, 'Saturday 28 February 2026'), (2, 'Sunday 1 March 2026'), (3, 'Monday 30 December 2024'), (4, None), (5, 'Thursday 29 February 2024'), (6, 'Wednesday 31 December 1969'), (7, 'Sunday 3 January 2027')]

Keep only the events on a Sunday:

run(f"SELECT id FROM {TABLE} WHERE dayname(d) = 'Sunday' ORDER BY id LIMIT 10")

[(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 dayname() is always computed by the Query Engine:

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

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

plan(f"SELECT id FROM {TABLE} WHERE dayname(d) = 'Sunday'")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│  (dayname(d) = 'Sunday')  │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘

Make it faster

• Store the day if you filter on it often. A day of the week recurs every week, so no single range of dates selects it. Compute the day (its name or its dayofweek number) 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, dayname(d) = 'Sunday' isn't.
• Narrow the dates first. In d >= DATE '2026-01-01' AND dayname(d) = 'Sunday', the range on d is still evaluated in VAST DataBase, so dayname() runs only on the rows that pass it.

Limitations and errors

• English names only. dayname takes one argument; there is no way to choose the language. Map the names yourself, or map the dayofweek number, for other languages.
• No time-zone support. On a TIMESTAMP WITH TIME ZONE value, such as now(), dayname fails with an Extension Autoloading Error. Cast the value to TIMESTAMP first; see time zones.
• Not for TIME or INTERVAL. Both fail with No function matches the given name and argument types.
• TIMESTAMP_NS before 1970. Row 6's TIMESTAMP_NS value 1969-12-31 23:59:59.999999999 gives 'Thursday', while the TIMESTAMP value 1969-12-31 23:59:59.999999 gives '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.

run(f"SELECT id, dayname(tns), dayname(ts) FROM {TABLE} WHERE id = 6")

[(6, 'Thursday', 'Wednesday')]

Similar functions

run("SELECT dayname(DATE '2026-03-01'), strftime(DATE '2026-03-01', '%A'), strftime(DATE '2026-03-01', '%a'), "
    "dayofweek(DATE '2026-03-01'), isodow(DATE '2026-03-01'), monthname(DATE '2026-03-01')")

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

Clean up:

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

[]
[]

See also

• monthname: the name of the month.
• strftime: format a date with names and numbers.
• Date and time functions: all the date and time functions.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.