date_diff

Applies to VAST Cluster 5.5.

Functions › Date and time functions › Differences. Returns how many times a part, such as the month or the day, changes between two dates, timestamps or times: from 31 January to 1 February is one month, because the month changes. datediff is the same function. To count only complete periods, use date_sub.

Syntax

date_diff(part, start, end)
datediff(part, start, end)

Returns: BIGINT: positive when end is after start, negative when it's before.

Aliases: datediff.

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_date_diff. 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 events, each with a date (d), a timestamp (ts) and a time of day (t). 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_date_diff"'

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)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, DATE '2026-02-28', TIMESTAMP '2026-02-28 23:15:00', TIME '23:15:00'), "
    "(2, DATE '2026-03-01', TIMESTAMP '2026-03-01 08:30:45.123456', TIME '08:30:45.123456'), "
    "(3, DATE '2024-12-30', TIMESTAMP '2024-12-30 12:00:00', TIME '12:00:00'), "
    "(4, NULL, NULL, NULL), "
    "(5, DATE '2024-02-29', TIMESTAMP '2024-02-29 00:00:00', TIME '00:00:00')")

[]
[]
[(5,)]

What it does

date_diff counts the boundaries of part between start and end. From 2026-01-31 to 2026-02-01 is one month and one day; from 2025-12-31 to 2026-01-01 is one year. For timestamps the time counts too: from 23:59:59 to 00:00:00 the next day is one day, one hour and one second, and from 08:00:00 back to 07:59:59.999999 is -1 hour.

'week' is the exception: it counts whole seven-day periods, so from a Saturday to the next day is 0 weeks, and 29 days is 4.

These are the part names it accepts, with the result from TIMESTAMP '2024-02-29 13:45:30.123456' to TIMESTAMP '2026-03-01 08:30:45.5':

On TIME values, date_diff counts within one day: from TIME '23:00:00' to TIME '01:00:00' is -22 hours.

The part can come from a column, so each row can count in a different unit.

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, date_diff('day', d, DATE '2026-12-31') FROM {TABLE} WHERE id = 4")
run("SELECT date_diff(NULL, DATE '2026-01-01', DATE '2026-02-01'), date_diff('day', DATE '2026-01-01', DATE 'infinity'), "
    "date_diff('day', DATE '2026-01-01', '2026-02-01'), date_diff('YEAR', DATE '2024-02-29', DATE '2026-03-01')")
run("SELECT date_diff('yyyy', DATE '2024-02-29', DATE '2026-03-01')")
run("SELECT date_diff('nanosecond', DATE '2024-02-29', DATE '2026-03-01')")
run("SELECT date_diff('era', DATE '2024-02-29', DATE '2026-03-01')")
run("SELECT date_diff('day', TIME '08:00:00', TIME '09:00:00')")
run("SELECT date_diff('hour', TIME '08:00:00', TIMESTAMP '2026-03-01 09:00:00')")
run("SELECT date_diff('day', '2026-01-01', '2026-02-01')")
run("SELECT date_diff('day', 'abc', DATE '2026-12-31')")
run("SELECT date_diff('day', 123, DATE '2026-12-31')")

[(4, None)]
[(None, None, 31, 2)]
OSError: extract specifier "yyyy" not recognized
OSError: extract specifier "nanosecond" not recognized
OSError: Specifier type not implemented for DATEDIFF
OSError: "time" units "day" not recognized
InternalError: Binder Error: No function matches the given name and argument types 'date_diff(STRING_LITERAL, TIME, TIMESTAMP)'. You might need to add explicit type casts.
InternalError: Binder Error: Could not choose a best candidate function for the function call "date_diff(STRING_LITERAL, STRING_LITERAL, STRING_LITERAL)". In order to select one, please add explicit type casts.
OSError: invalid date field format: "abc", expected format is (YYYY-MM-DD)
InternalError: Binder Error: No function matches the given name and argument types 'date_diff(STRING_LITERAL, INTEGER_LITERAL, DATE)'. You might need to add explicit type casts.

Boundaries, not complete periods; and 'week', which counts whole weeks:

run("SELECT date_diff('month', DATE '2026-01-31', DATE '2026-02-01'), date_diff('year', DATE '2025-12-31', DATE '2026-01-01'), "
    "date_diff('day', TIMESTAMP '2026-03-01 23:59:59', TIMESTAMP '2026-03-02 00:00:00'), "
    "date_diff('hour', TIMESTAMP '2026-03-01 08:00:00', TIMESTAMP '2026-03-01 07:59:59.999999')")
run("SELECT date_diff('week', DATE '2026-03-07', DATE '2026-03-08'), date_diff('week', DATE '2026-01-31', DATE '2026-03-01'), "
    "date_diff('week', DATE '2026-03-01', DATE '2026-03-08'), date_diff('hour', TIME '23:00:00', TIME '01:00:00')")

[(1, 1, 1, -1)]
[(0, 4, 1, -22)]

Examples

The days from each event to the end of 2026, the hours from each timestamp to 1 March 2026, and the months to the end of 2026:

run(f"SELECT id, date_diff('day', d, DATE '2026-12-31'), datediff('hour', ts, TIMESTAMP '2026-03-01 00:00:00'), "
    f"date_diff('month', ts, TIMESTAMP '2026-12-31 00:00:00') FROM {TABLE} ORDER BY id LIMIT 10")

[(1, 306, 1, 10), (2, 305, -8, 9), (3, 731, 10212, 24), (4, None, None, None), (5, 1036, 17544, 34)]

The minutes from each time of day to noon, and the hours between each date and its timestamp:

run(f"SELECT id, date_diff('minute', t, TIME '12:00:00'), date_diff('hour', d, ts) FROM {TABLE} ORDER BY id LIMIT 10")

[(1, -675, 23), (2, 210, 8), (3, 0, 12), (4, None, None), (5, 720, 0)]

Keep only the events less than 306 days before the end of 2026:

run(f"SELECT id FROM {TABLE} WHERE date_diff('day', d, DATE '2026-12-31') < 306 ORDER BY id LIMIT 10")

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

• In the SELECT list, the scan reads the columns and the Query Engine computes date_diff() for each row it returns.
• In WHERE, the scan sends the columns for every row, and a FILTER step in the Query Engine computes date_diff() 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 date_diff('day', d, DATE '2026-12-31') < 306")

┌───────────────────────────┐
│         PROJECTION        │
│    ────────────────────   │
│             #1            │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│           FILTER          │
│    ────────────────────   │
│ (date_diff('day', d, '2026│
│   -12-31'::DATE) < 306)   │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│                           │
│        Projections:       │
│             d             │
│             id            │
│                           │
└───────────────────────────┘

Make it faster

• Compare the column with a computed constant. d > DATE '2026-12-31' - 306 keeps the same rows as date_diff('day', d, DATE '2026-12-31') < 306, and it's pushed down to VAST DataBase, so rows that don't match never leave storage. The constant side is computed once. Its plan has no FILTER step:

run(f"SELECT id FROM {TABLE} WHERE d > DATE '2026-12-31' - 306 ORDER BY id LIMIT 10")
plan(f"SELECT id FROM {TABLE} WHERE d > DATE '2026-12-31' - 306")

[(2,)]
┌───────────────────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│      Projections: id      │
│                           │
└───────────────────────────┘

• For timestamps, subtract an interval from the constant: ts > TIMESTAMP '2026-03-01 00:00:00' - INTERVAL 1 HOUR is pushed down; see -.

Limitations and errors

• No time-zone support. On TIMESTAMP WITH TIME ZONE values, such as now(), date_diff fails with an Extension Autoloading Error. Cast the values to TIMESTAMP first; see time zones.
• No nanoseconds. Use 'microseconds'; the fraction of a microsecond in a TIMESTAMP_NS value isn't counted.
• Other SQL dialects' names aren't available. timestampdiff fails with Scalar Function with name timestampdiff does not exist!, and part names such as 'yyyy', 'dd' and 'hh' aren't recognized. Use date_diff with the names in What it does.

run("SELECT date_diff('microsecond', TIMESTAMP '2026-02-28 23:15:00', TIMESTAMP_NS '2026-02-28 23:15:00.123456789')")
run("SELECT timestampdiff(DAY, DATE '2026-03-01', DATE '2026-03-08')")
run("SELECT date_diff('day', DATE '2026-03-01', DATE '2026-03-08')")

[(123456,)]
InternalError: Catalog Error: Scalar Function with name timestampdiff does not exist!
[(7,)]

Similar functions

From 08:59 to 09:01, date_diff('hour', ...) is 1 (the hour changes), date_sub('hour', ...) is 0, and the difference of the epochs is 120.0 seconds.

run("SELECT date_diff('month', DATE '2026-01-31', DATE '2026-03-01'), date_sub('month', DATE '2026-01-31', DATE '2026-03-01'), "
    "age(DATE '2026-03-01', DATE '2026-01-31'), DATE '2026-03-01' - DATE '2026-01-31'")
run("SELECT date_diff('hour', TIMESTAMP '2026-03-01 08:59:00', TIMESTAMP '2026-03-01 09:01:00'), "
    "date_sub('hour', TIMESTAMP '2026-03-01 08:59:00', TIMESTAMP '2026-03-01 09:01:00'), "
    "epoch(TIMESTAMP '2026-03-01 09:01:00') - epoch(TIMESTAMP '2026-03-01 08:59:00')")

[(2, 1, MonthDayNano(months=1, days=1, nanoseconds=0), 29)]
[(1, 0, 120.0)]

Clean up:

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

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See also

• Date and time functions: all the date and time functions.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.