to_months

Applies to VAST Cluster 5.5.

Functions › Date and time functions › Interval constructors. Returns an interval of n months, the same as INTERVAL n MONTH. Add it to a date or a timestamp, or subtract it, to move by that many months.

Syntax

to_months(n)

Returns: INTERVAL.

Same as: INTERVAL n MONTH for a constant n.

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_to_months. 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 five tasks. Each has a start time (ts), a date (d), a whole number (n, an INTEGER) and a number with a fraction (f, a DOUBLE). 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_to_months"'

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}.tasks"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, ts TIMESTAMP, d DATE, n INTEGER, f DOUBLE)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, TIMESTAMP '2026-02-28 23:15:00', DATE '2026-01-31', 1, 1.5), "
    "(2, TIMESTAMP '2026-03-01 08:30:45.123456', DATE '2026-03-01', -2, -0.25), "
    "(3, TIMESTAMP '2024-12-30 12:00:00', DATE '2024-12-30', 0, 0.0), "
    "(4, NULL, NULL, NULL, NULL), "
    "(5, TIMESTAMP '2024-02-29 00:00:00', DATE '2024-02-29', 12, 0.000001)")

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[(5,)]

What it does

An INTERVAL has three parts: months, days and a time part. ADBC returns it as an Arrow month-day-nanosecond interval, which Python prints as MonthDayNano(months=..., days=..., nanoseconds=...). The parts are kept apart: they're combined only when the interval is added to a date or a timestamp.

to_months(n) puts n in the months part: to_months(2) is months=2. Months follow the calendar. Added to the last day of a month, the result is the last day of the shorter month: DATE '2026-01-31' + to_months(1) is 2026-02-28 00:00:00, a TIMESTAMP. TIMESTAMP '2024-02-29 00:00:00' + to_months(1) is 2024-03-29 00:00:00.

Months aren't turned into days: normalized_interval(to_months(100)) is still 100 months. Where an interval of months has to be measured, a month counts as 30 days: INTERVAL 1 MONTH = INTERVAL 30 DAY is true, and epoch(to_months(1)) is 2592000.0 seconds (30 days).

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, to_months(n) FROM {TABLE} WHERE id = 4")
run("SELECT to_months(NULL), to_months(0), to_months(-1), to_months('2'), to_months(CAST(2 AS SMALLINT))")
run("SELECT to_months(CAST(2 AS BIGINT))")
run("SELECT to_months(1.5)")
run("SELECT to_months(2147483647)")
run("SELECT to_months(2147483648)")
run("SELECT to_months(DATE '2026-01-01')")

[(4, None)]
[(None, MonthDayNano(months=0, days=0, nanoseconds=0), MonthDayNano(months=-1, days=0, nanoseconds=0), MonthDayNano(months=2, days=0, nanoseconds=0), MonthDayNano(months=2, days=0, nanoseconds=0))]
InternalError: Binder Error: No function matches the given name and argument types 'to_months(BIGINT)'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'to_months(DECIMAL(2,1))'. You might need to add explicit type casts.
[(MonthDayNano(months=2147483647, days=0, nanoseconds=0),)]
InternalError: Binder Error: No function matches the given name and argument types 'to_months(INTEGER_LITERAL)'. You might need to add explicit type casts.
InternalError: Binder Error: No function matches the given name and argument types 'to_months(DATE)'. You might need to add explicit type casts.

Examples

An interval of n months for each task:

run(f"SELECT id, n, to_months(n) FROM {TABLE} ORDER BY id LIMIT 10")

[(1, 1, MonthDayNano(months=1, days=0, nanoseconds=0)), (2, -2, MonthDayNano(months=-2, days=0, nanoseconds=0)), (3, 0, MonthDayNano(months=0, days=0, nanoseconds=0)), (4, None, None), (5, 12, MonthDayNano(months=12, days=0, nanoseconds=0))]

Move each start time by n months, and the last day of January by one month:

run(f"SELECT id, ts, ts + to_months(n) FROM {TABLE} ORDER BY id LIMIT 10")
run("SELECT DATE '2026-01-31' + to_months(1), TIMESTAMP '2024-02-29 00:00:00' + to_months(1), TIMESTAMP '2024-02-29 00:00:00' - to_months(1)")

[(1, datetime.datetime(2026, 2, 28, 23, 15), datetime.datetime(2026, 3, 28, 23, 15)), (2, datetime.datetime(2026, 3, 1, 8, 30, 45, 123456), datetime.datetime(2026, 1, 1, 8, 30, 45, 123456)), (3, datetime.datetime(2024, 12, 30, 12, 0), datetime.datetime(2024, 12, 30, 12, 0)), (4, None, None), (5, datetime.datetime(2024, 2, 29, 0, 0), datetime.datetime(2025, 2, 28, 0, 0))]
[(datetime.datetime(2026, 2, 28, 0, 0), datetime.datetime(2024, 3, 29, 0, 0), datetime.datetime(2024, 1, 29, 0, 0))]

Keep only the tasks that, moved by n months, end after midnight on 1 March 2026:

run(f"SELECT id FROM {TABLE} WHERE ts + to_months(n) > TIMESTAMP '2026-03-01 00:00:00' ORDER BY id LIMIT 10")

[(1,)]

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 an interval built from a column is always computed by the Query Engine:

• In the SELECT list, the scan reads the column and the Query Engine computes to_months() for each row it returns.
• In WHERE, the scan sends the columns for every row, and a FILTER step in the Query Engine computes ts + to_months(n) 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 ts + to_months(n) > TIMESTAMP '2026-03-01 00:00:00'")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #2            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│  ((ts + to_months(n)) >   │
│   '2026-03-01 00:00:00':  │
│        :TIMESTAMP)        │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             ts            │
│             n             │
│             id            │
│                           │
└───────────────────────────┘

Make it faster

• Put the interval on the constant side. A comparison of the raw column with a constant, such as ts > TIMESTAMP '2026-01-15 00:00:00' + to_days(30) or ts > TIMESTAMP '2026-03-01 00:00:00' - INTERVAL 1 HOUR, is pushed down to VAST DataBase, so rows that don't match never leave storage. ts + INTERVAL 1 HOUR > ... needs the FILTER step. The plan of the same shape with to_months:

plan(f"SELECT id FROM {TABLE} WHERE ts > TIMESTAMP '2026-03-01 00:00:00' - to_months(1)")

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

• Store the result if you filter on it often. When the number of months comes from a column, as n does here, there's no single constant to compare with. Compute ts + to_months(n) when you write the rows and keep it in its own TIMESTAMP column; a comparison of that column with a constant is pushed down.

Limitations and errors

• INTEGER only. A BIGINT, the type of most ID and count columns, fails with No function matches the given name and argument types 'to_months(BIGINT)'. Cast it with CAST(id AS INTEGER). A fraction fails the same way: use to_days for part of a month.
• Range. to_months(2147483647) is the largest accepted value; to_months(2147483648) fails with No function matches the given name and argument types 'to_months(INTEGER_LITERAL)': the number doesn't fit in an INTEGER.
• No INTERVAL columns. A table can't have an INTERVAL column: CREATE TABLE fails with INTERVAL type is not supported in table definitions. Store the number of months in a number column and build the interval with to_months() in the query.

run(f"SELECT id, to_months(id) FROM {TABLE} ORDER BY id LIMIT 10")
run(f"SELECT id, to_months(CAST(id AS INTEGER)) FROM {TABLE} ORDER BY id LIMIT 10")
run(f"CREATE TABLE {SCHEMA}.durations (id BIGINT, v INTERVAL)")

InternalError: Binder Error: No function matches the given name and argument types 'to_months(BIGINT)'. You might need to add explicit type casts.
[(1, MonthDayNano(months=1, days=0, nanoseconds=0)), (2, MonthDayNano(months=2, days=0, nanoseconds=0)), (3, MonthDayNano(months=3, days=0, nanoseconds=0)), (4, MonthDayNano(months=4, days=0, nanoseconds=0)), (5, MonthDayNano(months=5, days=0, nanoseconds=0))]
InternalError: Binder Error: INTERVAL type is not supported in table definitions. Column "v" has type: INTERVAL

Similar functions

run("SELECT to_months(1) = INTERVAL 1 MONTH, to_months(1) = to_days(30)")
run(f"SELECT id, to_months(CAST(id AS INTEGER)) = INTERVAL (id) MONTH FROM {TABLE} ORDER BY id LIMIT 10")
run("SELECT date_add(TIMESTAMP '2024-02-29 00:00:00', to_months(1)), normalized_interval(to_months(100))")

[(True, True)]
[(1, True), (2, True), (3, True), (4, True), (5, True)]
[(datetime.datetime(2024, 3, 29, 0, 0), MonthDayNano(months=100, days=0, nanoseconds=0))]

Clean up:

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

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See also

• The other interval constructors: to_years, to_quarters, to_weeks, to_days, to_hours, to_minutes, to_seconds, to_milliseconds, to_microseconds.
• Date and time functions: all the date and time functions.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.