--- title: "repeat (BLOB)" slug: "dev-database-reference-sql-functions-binary-hash-uuid-repeat" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-binary-hash-uuid-repeat" --- > ## Documentation Index > Fetch the complete documentation index at: https://docs.vastdata.com/llms.txt > Use this file to discover all available pages before exploring further. # repeat (BLOB) *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Binary, hash and UUID functions](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid) › Binary data and encodings.* Returns the bytes of a `BLOB` repeated `n` times, as a `BLOB`. This page covers `repeat` on bytes; for a string, see [repeat](/develop/docs/dev-database-reference-sql-functions-string-repeat), and for `repeat` in `FROM`, which makes rows, see [repeat (table function)](/develop/docs/dev-database-reference-sql-functions-table-functions-repeat). ## Syntax ``` repeat(b, n) ``` | Argument | Type | Description | | --- | --- | --- | | `b` | `BLOB` | The bytes to repeat. | | `n` | `BIGINT` | How many times. A constant or a column; a string such as `'2'` is converted. | **Returns:** `BLOB`. ## Set up the examples The examples connect with the ADBC driver, as in [VAST Query Engine (ADBC)](/develop/docs/dev-database-integrations-adbc), and work in a schema called `docs_sql_fn_binary_hash_uuid_repeat`. Set `QE_ENDPOINT`, `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY` and `VASTDB_BUCKET` ([SQL reference](/develop/docs/dev-database-reference-sql-index#example-connect-and-use-a-transaction)), 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 patterns, each with its bytes and a repeat count. The last row has no bytes: ``` 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_binary_hash_uuid_repeat"' 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, "") 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}.patterns" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, data BLOB, n BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, '\\x25\\x50\\x44\\x46'::BLOB, 2), " "(2, ''::BLOB, 5), " "(3, '\\x00\\x01'::BLOB, 3), " "(4, '\\x61'::BLOB, -1), " "(5, NULL, 2)") ``` ``` [] [] [(5,)] ``` ## What it does `repeat(b, n)` joins `n` copies of the bytes of `b`: `repeat('ab'::BLOB, 3)` gives `b'ababab'`. Every byte is copied as it is, zero bytes and bytes that aren't valid UTF-8 included, and the result is `n` times as long as `b`. An `n` of 0 or less gives empty bytes, not an error. The type of the first argument picks the function: a `BLOB` gives a `BLOB`, and a `VARCHAR` gives a `VARCHAR` ([repeat](/develop/docs/dev-database-reference-sql-functions-string-repeat) for strings). A string constant such as `'ab'` is a `VARCHAR`, so cast it, `'ab'::BLOB`, to repeat bytes. ## NULLs and edge cases | Input | Result | | --- | --- | | `b` is NULL | `NULL` | | `n` is NULL | `NULL` | | `n` is `0` or negative | `b''` (empty bytes) | | `n` is `1` | `b` unchanged | | `b` is `''::BLOB` | `b''` | | `repeat('\x00'::BLOB, 4)` | four zero bytes | | `n` a string: `repeat('ab'::BLOB, '2')` | `b'abab'`: the string is converted to a number | | `n` a `DECIMAL`: `repeat('ab'::BLOB, 2.6)` | Error: `No function matches the given name and argument types` | | A result too large to build | Error: `Cannot create a string of size ...` | The same cases, as the cluster returns them. They use the helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-repeat#set-up-the-examples): ``` run("SELECT repeat(NULL::BLOB, 2), repeat('ab'::BLOB, NULL), repeat('ab'::BLOB, 0), repeat('ab'::BLOB, -1), repeat('ab'::BLOB, 1)") run("SELECT repeat(''::BLOB, 5), repeat('\\x00'::BLOB, 4), repeat('ab'::BLOB, '2')") run("SELECT repeat('ab'::BLOB, 2.6)") run("SELECT repeat('ab'::BLOB, 9223372036854775807)") ``` ``` [(None, None, b'', b'', b'ab')] [(b'', b'\x00\x00\x00\x00', b'abab')] InternalError: Binder Error: No function matches the given name and argument types 'repeat(BLOB, DECIMAL(2,1))'. You might need to add explicit type casts. OSError: Cannot create a string of size: '-2', the maximum supported string size is: '4294967295' ``` ## Examples Each pattern repeated three times: ``` run(f"SELECT id, repeat(data, 3) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, b'%PDF%PDF%PDF'), (2, b''), (3, b'\x00\x01\x00\x01\x00\x01'), (4, b'aaa'), (5, None)] ``` The count can come from a column. Row 4's count is negative, so it gives empty bytes: ``` run(f"SELECT id, repeat(data, n), octet_length(repeat(data, n)) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, b'%PDF%PDF', 8), (2, b'', 0), (3, b'\x00\x01\x00\x01\x00\x01', 6), (4, b'', 0), (5, None, None)] ``` ## 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`). `repeat()` of a column is computed by the Query Engine: - **In the `SELECT` list,** the scan reads the columns and the Query Engine builds the repeated bytes for each row it returns. - **In `WHERE`,** the scan sends the columns for every row, and a `FILTER` step in the Query Engine computes `repeat()` and keeps the rows that match. The plan of a filter on `repeat()` shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE repeat(data, 3) IS NOT NULL") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (repeat(data, 3) IS NOT │ │ NULL) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ data │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Test the source column, not the repeated bytes.** `repeat(data, 3)` is NULL only when `data` is, and a test of the column itself, such as `data IS NULL`, is evaluated in VAST DataBase. The plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE data IS NULL") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Build large values only in the `SELECT` list.** A repeated value is as large as `n` copies of the input, for every row it's computed on; compute it on the rows you return, after the other conditions have filtered them. ## Limitations and errors - **A whole-number count.** A `DECIMAL` count fails with `No function matches the given name and argument types`, and the error lists the forms of `repeat`: `repeat(VARCHAR, BIGINT)`, `repeat(BLOB, BIGINT)` and `repeat(ANY[], BIGINT)`. Round the count and cast it to `BIGINT`. - **A size limit.** A count so large that the result can't be built fails with `Cannot create a string of size ...`. - **Not the table function.** In `FROM`, `repeat(value, n)` returns `n` rows instead: see [repeat (table function)](/develop/docs/dev-database-reference-sql-functions-table-functions-repeat). ``` run("SELECT repeat('ab'::BLOB, CAST(round(2.6) AS BIGINT))") ``` ``` [(b'ababab',)] ``` ## Similar functions | Function | Repeats | Result for `('ab', 2)` | | --- | --- | --- | | `repeat` on a `BLOB` | bytes | `repeat('ab'::BLOB, 2)` gives `b'abab'`, a `BLOB` | | [repeat](/develop/docs/dev-database-reference-sql-functions-string-repeat) on a `VARCHAR` | characters | `repeat('ab', 2)` gives `'abab'`, a `VARCHAR` | | [repeat (table function)](/develop/docs/dev-database-reference-sql-functions-table-functions-repeat) | rows | `SELECT * FROM repeat('ab', 2)` gives two rows of `'ab'` | | `\|\|` on `BLOB` values ([BLOB values](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid-blob-values)) | joins two values | `'ab'::BLOB` `\|\|` `'ab'::BLOB` gives `b'abab'` | ``` run("SELECT repeat('ab'::BLOB, 2), typeof(repeat('ab'::BLOB, 2)), repeat('ab', 2), typeof(repeat('ab', 2))") run("SELECT * FROM repeat('ab', 2) LIMIT 10") run("SELECT 'ab'::BLOB || 'ab'::BLOB") ``` ``` [(b'abab', 'BLOB', 'abab', 'VARCHAR')] [('ab',), ('ab',)] [(b'abab',)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Binary, hash and UUID functions](/develop/docs/dev-database-reference-sql-functions-binary-hash-uuid): all the functions in this family. - [Data types in SQL](/develop/docs/dev-database-reference-sql-data-types): `BLOB` columns. - [Where filters run](/develop/docs/dev-database-reference-sql-select#where-filters-run) and [pushdowns](/develop/docs/dev-database-reference-pushdowns). - [EXPLAIN](/develop/docs/dev-database-reference-sql-explain): how to read a plan.