last_day

Applies to VAST Cluster 5.5.

Functions › Date and time functions › Names and calendar. Returns the last day of the month of a date or timestamp, as a DATE. Leap years are taken into account.

Syntax

last_day(value)

Returns: DATE, also for a TIMESTAMP.

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_last_day. 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 5 is a leap day, and row 6 is the last moment of 1969:

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_last_day"'

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))")

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[]
[(7,)]

What it does

last_day returns the date of the last day of the month that the value falls in. February follows the Gregorian leap-year rule: a year divisible by 4 is a leap year, except a century year that isn't divisible by 400:

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, last_day(ts) FROM {TABLE} WHERE id = 4")
run("SELECT last_day(DATE '2024-02-10'), last_day(DATE '2023-02-10'), last_day(DATE '2000-02-10'), "
    "last_day(DATE '1900-02-10'), last_day(DATE '2026-12-31')")
run("SELECT last_day(TIMESTAMP '2026-04-30 23:59:59'), typeof(last_day(TIMESTAMP '2026-04-30 23:59:59'))")
run("SELECT last_day(NULL), last_day(DATE 'infinity'), last_day(TIMESTAMP '-infinity'), "
    "last_day(DATE '0001-01-01'), last_day(DATE '9999-12-31'), last_day(TIMESTAMP '1969-12-31 23:59:59.999999')")
run("SELECT last_day(INTERVAL 1 MONTH)")
run("SELECT last_day(TIME '13:45:30')")
run("SELECT last_day('2026-03-01')")
run("SELECT last_day(123)")

[(4, None)]
[(datetime.date(2024, 2, 29), datetime.date(2023, 2, 28), datetime.date(2000, 2, 29), datetime.date(1900, 2, 28), datetime.date(2026, 12, 31))]
[(datetime.date(2026, 4, 30), 'DATE')]
[(None, None, None, datetime.date(1, 1, 31), datetime.date(9999, 12, 31), datetime.date(1969, 12, 31))]
InternalError: Binder Error: No function matches the given name and argument types 'last_day(INTERVAL)'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'last_day(TIME)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "last_day(STRING_LITERAL)". In order to select one, please add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'last_day(INTEGER_LITERAL)'. You might need to add explicit type casts.

Examples

The last day of each event's month:

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

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

The number of days in each event's month is the day of the month of its last day, with day:

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

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

Keep only the events on the last day of a month:

run(f"SELECT id, d FROM {TABLE} WHERE last_day(d) = d ORDER BY id LIMIT 10")

[(1, datetime.date(2026, 2, 28)), (5, datetime.date(2024, 2, 29)), (6, datetime.date(1969, 12, 31))]

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 last_day() is always computed by the Query Engine:

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

The plan of the last-day example shows the FILTER step above the scan:

plan(f"SELECT id, d FROM {TABLE} WHERE last_day(d) = d")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             id            │
│             d             │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│     (last_day(d) = d)     │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘

Make it faster

• For one month, filter on a range of the raw column. To select a month, compare the column with its first day and the first day of the next month, such as d >= DATE '2026-02-01' AND d < DATE '2026-03-01', rather than with last_day(d). 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, d FROM {TABLE} WHERE d >= DATE '2026-02-01' AND d < DATE '2026-03-01'")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             id            │
│             d             │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘

• Store a flag if you filter on month ends often. last_day(d) = d must be computed for every row. Compute it when you write the rows and keep it in its own column: is_month_end = true is pushed down, last_day(d) = d isn't.

Limitations and errors

• No time-zone support. On a TIMESTAMP WITH TIME ZONE value, such as now(), last_day 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 1970-01-31, while the TIMESTAMP value 1969-12-31 23:59:59.999999 gives 1969-12-31. If you need the month of nanosecond values before 1970 that are close to midnight at a month end, check the result or store the value as TIMESTAMP.

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

[(6, datetime.date(1970, 1, 31), datetime.date(1969, 12, 31))]

Similar functions

run("SELECT last_day(DATE '2024-02-10'), date_trunc('month', DATE '2024-02-10'), "
    "date_trunc('month', DATE '2024-02-10') + INTERVAL 1 MONTH - INTERVAL 1 DAY, "
    "CAST(date_trunc('month', DATE '2024-02-10') + INTERVAL 1 MONTH - INTERVAL 1 DAY AS DATE), "
    "make_date(2024, 3, 1) - 1")

[(datetime.date(2024, 2, 29), datetime.date(2024, 2, 1), datetime.datetime(2024, 2, 29, 0, 0), datetime.date(2024, 2, 29), datetime.date(2024, 2, 29))]

Clean up:

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

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See also

• date_trunc: the first day of the month, week or year.
• day and month: parts of a date.
• Date and time functions: all the date and time functions.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.