--- title: "cbrt" slug: "dev-database-reference-sql-functions-numeric-cbrt" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-cbrt" --- > ## 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. # cbrt *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric) › Powers and logarithms.* Returns the cube root of a number, as a `DOUBLE`. Unlike a fractional power, it takes negative numbers: `cbrt(-8.0::DOUBLE)` is `-2.0`. ## Syntax ``` cbrt(x) ``` | Argument | Type | Description | | --- | --- | --- | | `x` | `DOUBLE` (any number) | The number to take the cube root of. It can be negative. | **Returns:** `DOUBLE`, whatever the argument type. ## 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_numeric_cbrt`. 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 three cube-shaped tanks: the volume of each, and the change in volume since the last reading, which can be negative. 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_numeric_cbrt"' 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}.tanks" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, volume DOUBLE, change DOUBLE)") run(f"INSERT INTO {TABLE} VALUES " "(1, 8.0, -8.0), " "(2, 1000.0, 125.0), " "(3, 2.0, -0.5), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `cbrt(x)` returns the number whose cube is `x`. It's defined for every real number, so a negative `x` gives a negative root: `cbrt(-8.0::DOUBLE)` is `-2.0`. That's the difference from a power: `pow(-27, 1.0 / 3)` is `nan`, while `cbrt(-27)` is about `-3`. The argument is converted to `DOUBLE` first, so integers, `DECIMAL` and `FLOAT` values all work and all give a `DOUBLE`; so does a string that holds a number: `cbrt('12')` is `2.2894284851066633`. **The result is rounded to the nearest `DOUBLE`,** so a perfect cube doesn't always give a whole number: `cbrt(27)` is `3.0000000000000004`, and `cbrt(27) = 3` is false. Round the result, or compare it with a tolerance, before you test it for equality. Floating-point special values pass through: `inf` gives `inf`, `-inf` gives `-inf`, `nan` gives `nan`, and `-0.0` gives `-0.0`. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `cbrt(27)` | `3.0000000000000004` | | `cbrt(-27)` | `-3.0000000000000004` | | `cbrt(-8.0::DOUBLE)` | `-2.0` | | `cbrt(2)` | `1.2599210498948734` | | `cbrt(0)` | `0.0` | | `cbrt(-0.0::DOUBLE)` | `-0.0` | | `cbrt(1e300)`, `cbrt(-1e-300)` | `1e+100`, `-1e-100` | | `cbrt('inf'::DOUBLE)`, `cbrt('-inf'::DOUBLE)`, `cbrt('nan'::DOUBLE)` | `inf`, `-inf`, `nan` | | `cbrt(27) = 3` | `False` | | `cbrt(27::FLOAT)` | a `DOUBLE` | | `cbrt('12')` | `2.2894284851066633` | | `cbrt('abc')` | Error: `Could not convert string 'abc' to DOUBLE` | | A boolean, date, interval, `BLOB` or list | Error: `No function matches the given name and argument types`, for example `'cbrt(BOOLEAN)'` | The same cases, as the cluster returns them. They use the table and helpers from [Set up the examples](/develop/docs/dev-database-reference-sql-functions-numeric-cbrt#set-up-the-examples): ``` run("SELECT cbrt(NULL), cbrt(27), cbrt(-27), cbrt(-8.0::DOUBLE), cbrt(2)") run("SELECT cbrt(0), cbrt(-0.0::DOUBLE), cbrt(1e300), cbrt(-1e-300)") run("SELECT cbrt('inf'::DOUBLE), cbrt('-inf'::DOUBLE), cbrt('nan'::DOUBLE), cbrt(27) = 3, typeof(cbrt(27::FLOAT))") run(f"SELECT cbrt('12') FROM {TABLE} LIMIT 1") run(f"SELECT cbrt('abc') FROM {TABLE} LIMIT 1") run("SELECT cbrt(true)") ``` ``` [(None, 3.0000000000000004, -3.0000000000000004, -2.0, 1.2599210498948734)] [(0.0, -0.0, 1e+100, -1e-100)] [(inf, -inf, nan, False, 'DOUBLE')] [(2.2894284851066633,)] OSError: Could not convert string 'abc' to DOUBLE InternalError: Binder Error: No function matches the given name and argument types 'cbrt(BOOLEAN)'. You might need to add explicit type casts. ``` ## Examples The side of each tank, and the cube root of the change in volume, which keeps its sign: ``` run(f"SELECT id, cbrt(volume), cbrt(change) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 2.0, -2.0), (2, 10.0, 5.0), (3, 1.2599210498948734, -0.7937005259840998), (4, None, None)] ``` Keep only the tanks with a side longer than 5: ``` run(f"SELECT id, volume FROM {TABLE} WHERE cbrt(volume) > 5 ORDER BY id LIMIT 10") ``` ``` [(2, 1000.0)] ``` Round before you compare a root with a whole number: ``` run("SELECT cbrt(27), cbrt(27) = 3, round(cbrt(27), 9) = 3") ``` ``` [(3.0000000000000004, False, True)] ``` ## 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 `cbrt()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `cbrt()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `cbrt()` 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 cbrt(volume) > 5") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (cbrt(volume) > 5.0) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ volume │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Cube the constant instead.** A larger number always has a larger cube root, so `cbrt(volume) > 5` is the same as `volume > 125`, and that comparison of the raw column with a constant is pushed down to VAST DataBase, so rows that don't match never leave storage. Its plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE volume > 125") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Store the root if you filter on it often.** Compute it when you write the rows and keep it in its own column. - **Combine it with a pushed-down condition.** In `id > 100 AND cbrt(volume) > 5`, `id > 100` is still evaluated in VAST DataBase, so `cbrt()` runs only on the rows that pass it. ## Limitations and errors - **Numbers only.** A boolean, date, interval, `BLOB` or list fails with `No function matches the given name and argument types`; the error lists the one form `cbrt` accepts, `cbrt(DOUBLE) -> DOUBLE`. A string is converted when the query runs, and one that isn't a number fails with `Could not convert string 'abc' to DOUBLE`. - **Not exact.** See [What it does](/develop/docs/dev-database-reference-sql-functions-numeric-cbrt#what-it-does): round before you test a root for equality. - **No `cube_root`.** It fails with `Scalar Function with name cube_root does not exist!`. Use `cbrt`. ``` run("SELECT cube_root(8)") ``` ``` InternalError: Catalog Error: Scalar Function with name cube_root does not exist! ``` ## Similar functions | Function | Computes | Result for 27 | Result for -27 | | --- | --- | --- | --- | | `cbrt(x)` | the cube root | `3.0000000000000004` | `-3.0000000000000004` | | [pow](/develop/docs/dev-database-reference-sql-functions-numeric-pow) `(x, 1.0 / 3)` | the cube root of a non-negative number, as a power | `3.0` | `nan` | | [sqrt](/develop/docs/dev-database-reference-sql-functions-numeric-sqrt) | the square root; a negative number fails | `sqrt(1024)` is `32.0` | (error) | ``` run("SELECT cbrt(27), pow(27, 1.0 / 3), cbrt(-27), pow(-27, 1.0 / 3)") run("SELECT sqrt(1024), cbrt(1024)") ``` ``` [(3.0000000000000004, 3.0, -3.0000000000000004, nan)] [(32.0, 10.079368399158987)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Numeric and math functions](/develop/docs/dev-database-reference-sql-functions-numeric): all the numeric functions. - [sqrt](/develop/docs/dev-database-reference-sql-functions-numeric-sqrt) and [pow](/develop/docs/dev-database-reference-sql-functions-numeric-pow). - [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.