--- title: "log10" slug: "dev-database-reference-sql-functions-numeric-log10" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-numeric-log10" --- > ## 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. # log10 *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 base-10 logarithm of a number, as a `DOUBLE`. `log(x)` with one argument returns the same. Zero and negative numbers fail the query. ## Syntax ``` log10(x) ``` | Argument | Type | Description | | --- | --- | --- | | `x` | `DOUBLE` (any number) | The number to take the logarithm of. It must be greater than 0. | **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_log10`. 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 four files and their sizes in bytes. One file is empty; 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_log10"' 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}.files" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, size BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, 1536), " "(2, 5000000), " "(3, 1), " "(4, 0), " "(5, NULL)") ``` ``` [] [] [(5,)] ``` ## What it does `log10(x)` returns the power that 10 must be raised to to give `x`: `log10(1)` is `0.0`, `log10(1000)` is `3.0` and `log10(0.001)` is `-3.0`. It's the same as [log](/develop/docs/dev-database-reference-sql-functions-numeric-log) with one argument. 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. The base-10 logarithm tells you the order of magnitude of a number, so it's a common way to put very different sizes on one scale: `log10(1e308)` is `308.0`, and `log10(5e-324::DOUBLE)`, the smallest `DOUBLE` above 0, is `-323.3062153431158`. **Zero and negative numbers are errors,** not infinity or NaN: `log10(0)` fails with `cannot take logarithm of zero`, and `log10(-1)` with `cannot take logarithm of a negative number`. The error stops the whole query: if one row of a column is 0 or negative, `log10()` of that column fails for every row, also in `WHERE`. A negative zero (`-0.0::DOUBLE`) counts as zero, and `'-inf'::DOUBLE` as negative. `log10('inf'::DOUBLE)` is `inf` and `log10('nan'::DOUBLE)` is `nan`. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `log10(1)` | `0.0` | | `log10(1000)`, `log10(0.001)` | `3.0`, `-3.0` | | `log10(1e308)` | `308.0` | | `log10(5e-324::DOUBLE)` | `-323.3062153431158` | | `log10('inf'::DOUBLE)`, `log10('nan'::DOUBLE)` | `inf`, `nan` | | `log10(100::INTEGER)` | a `DOUBLE` | | `log10(100::FLOAT)` | `2.0` | | `log10('12')` | `1.0791812460476249` | | `log10(0)`, `log10(-0.0::DOUBLE)` | Error: `cannot take logarithm of zero` | | `log10(-1)`, `log10('-inf'::DOUBLE)` | Error: `cannot take logarithm of a negative number` | | `log10('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 `'log10(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-log10#set-up-the-examples): ``` run("SELECT log10(NULL), log10(1), log10(1000), log10(0.001), log10(1e308), log10(5e-324::DOUBLE)") run("SELECT log10('inf'::DOUBLE), log10('nan'::DOUBLE), typeof(log10(100::INTEGER)), log10(100::FLOAT)") run(f"SELECT log10('12') FROM {TABLE} LIMIT 1") run("SELECT log10(0)") run("SELECT log10(-0.0::DOUBLE)") run("SELECT log10(-1)") run("SELECT log10('-inf'::DOUBLE)") run(f"SELECT log10('abc') FROM {TABLE} LIMIT 1") run("SELECT log10(true)") ``` ``` [(None, 0.0, 3.0, -3.0, 308.0, -323.3062153431158)] [(inf, nan, 'DOUBLE', 2.0)] [(1.0791812460476249,)] OSError: cannot take logarithm of zero OSError: cannot take logarithm of zero OSError: cannot take logarithm of a negative number OSError: cannot take logarithm of a negative number OSError: Could not convert string 'abc' to DOUBLE InternalError: Binder Error: No function matches the given name and argument types 'log10(BOOLEAN)'. You might need to add explicit type casts. ``` ## Examples The base-10 logarithm of each file size, and the number of digits in it, `floor(log10(size)) + 1`. The empty file is left out with `size > 0`, because `log10(0)` fails: ``` run(f"SELECT id, size, log10(size), floor(log10(size)) + 1 FROM {TABLE} WHERE size > 0 ORDER BY id LIMIT 10") ``` ``` [(1, 1536, 3.186391215695493, 4.0), (2, 5000000, 6.698970004336019, 7.0), (3, 1, 0.0, 1.0)] ``` Keep only the files of 1,000 bytes or more, by their logarithm. `size > 0` is evaluated in VAST DataBase, so the empty file never reaches `log10()`: ``` run(f"SELECT id, size FROM {TABLE} WHERE size > 0 AND log10(size) >= 3 ORDER BY id LIMIT 10") ``` ``` [(1, 1536), (2, 5000000)] ``` ## 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 `log10()` of a column is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `log10()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row that passes the pushed-down conditions, and a `FILTER` step in the Query Engine computes `log10()` and keeps the rows that match. Without a condition such as `size > 0`, every row's value reaches `log10()`, and a zero fails the query. The plan of the `WHERE` example shows the `FILTER` step above the scan. It holds only the `log10()` condition: `size > 0` is evaluated in the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE size > 0 AND log10(size) >= 3") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (log10(CAST(size AS DOUBLE│ │ )) >= 3.0) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ size │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Raise 10 to the constant instead.** A larger number always has a larger logarithm, so `log10(size) >= 6` is the same as `size >= 1000000`. That comparison of the raw column with a constant is pushed down to VAST DataBase, so rows that don't match never leave storage, and it never takes a logarithm, so the empty file doesn't fail it. `log10(size) >= 6` on its own fails on that file: ``` run(f"SELECT id FROM {TABLE} WHERE log10(size) >= 6 ORDER BY id LIMIT 10") run(f"SELECT id FROM {TABLE} WHERE size >= 1000000 ORDER BY id LIMIT 10") plan(f"SELECT id FROM {TABLE} WHERE size >= 1000000") ``` ``` OSError: cannot take logarithm of zero [(2,)] ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Store the logarithm 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 log10(size) >= 3`, `id > 100` is still evaluated in VAST DataBase, so `log10()` runs only on the rows that pass it. ## Limitations and errors - **Zero or a negative value fails the whole query.** `log10(size)` over the whole table fails with `cannot take logarithm of zero`, because one file is empty, and returns no rows at all. To skip those rows, filter them out with a pushed-down condition such as `WHERE size > 0`. To keep them in the result with a NULL, use `CASE WHEN size > 0 THEN log10(size) END`. - **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 `log10` accepts, `log10(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`. ``` run(f"SELECT log10(size) FROM {TABLE}") run(f"SELECT id, CASE WHEN size > 0 THEN log10(size) END FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` OSError: cannot take logarithm of zero [(1, 3.186391215695493), (2, 6.698970004336019), (3, 0.0), (4, None), (5, None)] ``` ## Similar functions | Function | Base | Result for 100 (`log10` gives `2.0`) | | --- | --- | --- | | [log](/develop/docs/dev-database-reference-sql-functions-numeric-log) `(x)` | 10 | `2.0` | | [log](/develop/docs/dev-database-reference-sql-functions-numeric-log) `(10, x)` | 10, given as an argument | `2.0` | | [ln](/develop/docs/dev-database-reference-sql-functions-numeric-ln) | e | `4.605170185988092` | | [log2](/develop/docs/dev-database-reference-sql-functions-numeric-log2) | 2 | `6.643856189774724` | ``` run("SELECT log10(100), log(100), log(10, 100), ln(100), log2(100)") ``` ``` [(2.0, 2.0, 2.0, 4.605170185988092, 6.643856189774724)] ``` 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. - [log](/develop/docs/dev-database-reference-sql-functions-numeric-log), [ln](/develop/docs/dev-database-reference-sql-functions-numeric-ln) and [log2](/develop/docs/dev-database-reference-sql-functions-numeric-log2). - [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.