format

Applies to VAST Cluster 5.5.

Functions › Text basics › Formatting. Builds a string from a template, replacing each {} placeholder with the next value. A placeholder can name a position and a format specification, such as a width, an alignment or a number of decimals. format has no aliases.

Syntax

format(template, value, ...)

Returns: VARCHAR.

Aliases: none.

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_format. 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 four orders. The last row 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_format"'

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}.orders"
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, customer VARCHAR, qty BIGINT, amount DECIMAL(10, 2), ordered DATE)")
run(f"INSERT INTO {TABLE} VALUES "
    "(1, 'Ada Lovelace', 3, 1234.50, DATE '2026-10-01'), "
    "(2, 'Grace Hopper', 12, 89.99, DATE '2026-10-02'), "
    "(3, 'José Martí', 1, 15.00, DATE '2026-10-05'), "
    "(4, NULL, NULL, NULL, NULL)")

[]
[]
[(4,)]

What it does

format copies template and replaces each placeholder with a value, converted to text:

• {} takes the next value, from left to right.
• {0}, {1}, … take the value at that position, counting from 0, so a value can be used out of order.
• {:spec} formats the value with a specification after the colon.
• {{ and }} are a literal { and }.

Values that the template doesn't use are ignored: format('no placeholders', 1) returns 'no placeholders'.

Format specifications

A centred value with an odd number of spaces left over gets the extra space on its right, as ' c ' shows. A position and a specification combine: format('{1:>5}', 'a', 'b') returns ' b'. {:.2f} works on DOUBLE and DECIMAL values alike: format('{:.2f}', 2.5::DOUBLE) returns '2.50'.

How values are converted

With a plain {}, every type is accepted and converted to its text form:

A specification must suit the value's type: {:d} on a string or on a decimal such as 1.5 fails. See Limitations and errors.

NULLs and edge cases

A NULL among several values also makes the whole result NULL: format('{} {}', 'a', NULL) returns NULL. The second block converts the values in How values are converted.

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

run("SELECT format(NULL), format(NULL, 'a'), format('{}', NULL), format('[{}]', ''), format('no placeholders', 1)")
run("SELECT format('[{}]', 123), format('[{}]', 1.5), format('[{}]', DATE '2026-10-16'), format('[{}]', true), format('[{}]', ['a', 'b']), format('[{}]', '\\xAA'::BLOB), format('[{}]', 'xyz'::BLOB)")
run("SELECT format('{} {}', 1)")
run("SELECT format('{', 1)")
run("SELECT format('{:d}', 'x')")

[(None, None, None, '[]', 'no placeholders')]
[('[123]', '[1.5]', '[2026-10-16]', '[true]', '[[a, b]]', '[\\xAA]', '[xyz]')]
OSError: Argument index "1" out of range
OSError: invalid format string
OSError: Invalid type specifier "d" for formatting a value of type string

The specifications from the table above:

run("SELECT format('{:>8}|{:<8}|{:^8}', 'r', 'l', 'c'), format('{:.2f}', 3.14159), format('{:08.3f}', 3.14159), format('{:05d}', 42)")
run("SELECT format('{:+d}', 5), format('{:,}', 1234567), format('{:x}', 255), format('{:b}', 5), format('{:e}', 12345.678)")
run("SELECT format('{} {}', 'a', 'b'), format('{1} {0}', 'a', 'b'), format('{{}}', 1)")

[('       r|l       |   c    ', '3.14', '0003.142', '00042')]
[('+5', '1,234,567', 'ff', '101', '1.234568e+04')]
[('a b', 'b a', '{}')]

Examples

The templates are full of braces, so the next blocks build each statement with + rather than a Python f-string, where every brace would have to be doubled.

A sentence for each order, with a string, an integer and a date. The row with no values gives NULL:

run("SELECT id, format('{} ordered {} items on {}', customer, qty, ordered) FROM " + TABLE + " ORDER BY id LIMIT 10")

[(1, 'Ada Lovelace ordered 3 items on 2026-10-01'), (2, 'Grace Hopper ordered 12 items on 2026-10-02'), (3, 'José Martí ordered 1 items on 2026-10-05'), (4, None)]

Aligned columns for a fixed-width report: the name left-aligned in 14 characters, the quantity right-aligned in 4, and the amount with two decimals. coalesce replaces a missing name with (unknown):

run("SELECT id, format('{:<14}|{:>4}|{:.2f}', coalesce(customer, '(unknown)'), qty, amount) FROM " + TABLE
    + " ORDER BY id LIMIT 10")

[(1, 'Ada Lovelace  |   3|1234.50'), (2, 'Grace Hopper  |  12|89.99'), (3, 'José Martí    |   1|15.00'), (4, None)]

Find an order by its display code, an id padded with zeros to five digits:

run("SELECT id, customer FROM " + TABLE + " WHERE format('ORD-{:05d}', id) = 'ORD-00002' ORDER BY id LIMIT 10")

[(2, 'Grace Hopper')]

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 format() is always computed by the Query Engine:

• In the SELECT list, the scan reads the columns and the Query Engine computes format() for each row it returns.
• In WHERE, the scan sends the columns for every row, and a FILTER step in the Query Engine computes format() 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("SELECT id FROM " + TABLE + " WHERE format('ORD-{:05d}', id) = 'ORD-00002'")

┌───────────────────────────┐
│           FILTER          │
│    ────────────────────   │
│ (format('ORD-{:05d}', id) │
│       = 'ORD-00002')      │
│                           │
└─────────────┬─────────────┘
┌─────────────┴─────────────┐
│         VAST_SCAN         │
│    ────────────────────   │
│    Function: VAST_SCAN    │
│      Projections: id      │
│                           │
└───────────────────────────┘

Make it faster

• Filter on the raw value, and format only for display. format('ORD-{:05d}', id) = 'ORD-00002' keeps the same row as id = 2, but only the second is a comparison of a raw column with a constant, which is pushed down to VAST DataBase, so rows that don't match never leave storage. Its plan has no FILTER step:

plan("SELECT id FROM " + TABLE + " WHERE id = 2")

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

• Combine it with a pushed-down condition. In id > 100 AND format('{}', customer) = '...', id > 100 is still evaluated in VAST DataBase, so format() runs only on the rows that pass it.

Limitations and errors

• One value per placeholder. Fewer values than placeholders fails with Argument index "1" out of range: placeholders count from 0, so index 1 is the second placeholder.
• Balanced braces. An unclosed { fails with invalid format string. Write a literal brace as {{ or }}.
• The specification must suit the type. {:d} on a string fails with Invalid type specifier "d" for formatting a value of type string, and on a decimal such as 1.5 with Invalid type specifier "d" for formatting a value of type float. Cast the value first, or use a plain {}.
• A NULL value makes the whole result NULL. Replace it first with coalesce.
• {} placeholders, not % codes. For C-style %s and %d, use printf.

run("SELECT format('{} and {}', 'a')")
run("SELECT format('{:d}', 'x')")
run("SELECT format('{:d}', CAST('42' AS BIGINT)), format('{}', coalesce(NULL, '-'))")

OSError: Argument index "1" out of range
OSError: Invalid type specifier "d" for formatting a value of type string
[('42', '-')]

Similar functions

format accepts any type in a plain {}; printf's %s doesn't accept numbers. See printf.

run("SELECT format('{:05d}|{:.2f}|{}', 42, 3.14159, 'x'), printf('%05d|%.2f|%s', 42, 3.14159, 'x')")
run("SELECT format('{}', NULL), printf('%s', NULL), concat('a', NULL, 'b'), 'a' || NULL || 'b', concat_ws('-', 'a', NULL, 'b')")

[('00042|3.14|x', '00042|3.14|x')]
[(None, None, 'ab', None, 'a-b')]

Clean up:

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

[]
[]

See also

• Text basics: all the text functions.
• printf: the same job with C-style % codes.
• Where filters run and pushdowns.
• EXPLAIN: how to read a plan.