--- title: "query" slug: "dev-database-reference-sql-functions-table-functions-query" updated: 2026-10-30T18:18:46Z published: 2026-10-30T18:18:46Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-table-functions-query" --- > ## 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. # query *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Table functions](/develop/docs/dev-database-reference-sql-functions-table-functions) › Queries and tables named in a string.* Runs one `SELECT` statement given as a string and returns its rows, so it goes in the `FROM` clause. Use it when your code builds the statement as text. ## Syntax ``` query(sql) ``` | Argument | Type | Description | | --- | --- | --- | | `sql` | `VARCHAR` constant | One `SELECT` statement. | **Returns:** a table with the columns and rows of the statement. ## 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_table_functions_query`. 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 articles. The last row has no title or view count: ``` 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_table_functions_query"' 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}.articles" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, title VARCHAR, views BIGINT)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'Getting started', 120), " "(2, 'Vector search', 45), " "(3, 'Tuning queries', 300), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `query(sql)` parses the string as a statement and returns its result as a table, with the statement's column names and types. Inside the string, quote a table name as you would in a statement (`"<bucket>/<schema>".articles`) and double any single quote (`''`). - The string must be a constant. It can be built from constants with `||`, as in `query('SELECT ' || '1 AS x')`, but not taken from a column. - The statement can use anything a `SELECT` can: a table, another table function such as [range](/develop/docs/dev-database-reference-sql-functions-table-functions-range), or another `query()`. - The columns keep their types: `typeof(x)` on `query('SELECT 1.5 AS x')` is `DECIMAL(2,1)`. ## NULLs and edge cases | Input | Result | | --- | --- | | `query('SELECT ' \\|\\| '1 AS x')` | One row, `1` | | `query('SELECT * FROM query(''SELECT 7 AS y'')')` (nested) | One row, `7` | | `query(NULL)` | Error: `Parser Error: syntax error at or near "NULL"` | | `query('')` | Error: `Parser Error: Expected a single SELECT statement` | | `query('SELECT 1; SELECT 2')` (two statements) | Error: `Parser Error: Expected a single SELECT statement` | | `query('SELEC 1')` (invalid SQL) | Error: `Parser Error: syntax error at or near "SELEC"` | 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-table-functions-query#set-up-the-examples): ``` run("SELECT * FROM query('SELECT ' || '1 AS x')") run("SELECT * FROM query('SELECT * FROM query(''SELECT 7 AS y'')')") run("SELECT * FROM query(NULL)") run("SELECT * FROM query('')") run("SELECT * FROM query('SELECT 1; SELECT 2')") run("SELECT * FROM query('SELEC 1')") ``` ``` [(1,)] [(7,)] InternalError: Parse query: 'SELECT * FROM query(NULL)' failed with: Parser Error: syntax error at or near "NULL" InternalError: Parse query: 'SELECT * FROM query('')' failed with: Parser Error: Expected a single SELECT statement InternalError: Parse query: 'SELECT * FROM query('SELECT 1; SELECT 2')' failed with: Parser Error: Expected a single SELECT statement InternalError: Parse query: 'SELECT * FROM query('SELEC 1')' failed with: Parser Error: syntax error at or near "SELEC" ``` ## Examples A constant row, and the type of a column: ``` run("SELECT * FROM query('SELECT 42 AS answer')") run("SELECT typeof(x) FROM query('SELECT 1.5 AS x')") ``` ``` [(42,)] [('DECIMAL(2,1)',)] ``` The articles, from a statement held in a Python variable. `ORDER BY` needs a `LIMIT` ([SELECT](/develop/docs/dev-database-reference-sql-select)), inside the string as anywhere else: ``` statement = f"SELECT id, title FROM {TABLE} ORDER BY id LIMIT 10" run(f"SELECT * FROM query('{statement}')") ``` ``` [(1, 'Getting started'), (2, 'Vector search'), (3, 'Tuning queries'), (4, None)] ``` A condition can go inside the string or outside `query()`: ``` run(f"SELECT * FROM query('SELECT id, title FROM {TABLE} WHERE id = 2')") run(f"SELECT * FROM query('SELECT id, title FROM {TABLE}') WHERE id = 2") ``` ``` [(2, 'Vector search')] [(2, 'Vector search')] ``` Rows from another table function: ``` run("SELECT * FROM query('SELECT * FROM range(3)')") ``` ``` [(0,), (1,), (2,)] ``` ## How it runs in VAST The Query Engine runs on the cluster's CNodes. It plans the statement in the string as if you had written it in place of `query()`, so a query on a table starts with a scan in VAST DataBase (`VAST_SCAN`). A comparison of a column with a constant in the string's `WHERE` is evaluated in that scan, so the plan of `query('SELECT id FROM articles WHERE id = 2')` is a single `VAST_SCAN` step, with no `FILTER` step: ``` plan(f"SELECT * FROM query('SELECT id FROM {TABLE} WHERE id = 2')") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Write static statements as plain SQL.** `query()` helps only when the statement is built as text; otherwise run the statement directly. - **Put the conditions in the string.** A `WHERE` inside the statement is planned with the scan and [pushes down](/develop/docs/dev-database-reference-pushdowns) as usual, as the plan above shows. - **Select only the columns you need** in the string: the scan reads only the columns the statement uses. ## Limitations and errors - **One `SELECT` only.** Two statements, an empty string or any other statement (`INSERT`, `DROP TABLE`) fail with `Parser Error: Expected a single SELECT statement`. Run other statements directly. - **A constant string only.** A column can't be the argument: it fails with `Table function "query" does not support lateral join column parameters`, and `query(NULL)` fails with `Parser Error: syntax error at or near "NULL"`. - **In `FROM` only.** In the `SELECT` list it fails with `Binder Error: Function "query" is a table function but it was used as a scalar function. This function has to be called in a FROM clause (similar to a table).` - **Errors in the statement are reported as usual,** for example `Catalog Error: Table with name ... does not exist!` for a table that isn't there. ``` run("SELECT * FROM query('SELECT 1; SELECT 2')") run(f"SELECT * FROM query('INSERT INTO {TABLE} (id) VALUES (90)')") run(f"SELECT * FROM {TABLE}, query(title)") run("SELECT query('SELECT 1')") run(f"SELECT * FROM query('SELECT * FROM {SCHEMA}.nope')") ``` ``` InternalError: Parse query: 'SELECT * FROM query('SELECT 1; SELECT 2')' failed with: Parser Error: Expected a single SELECT statement InternalError: Parse query: 'SELECT * FROM query('INSERT INTO "/docs_sql_fn_table_functions_query".articles (id) VALUES (90)')' failed with: Parser Error: Expected a single SELECT statement InternalError: Binder Error: Table function "query" does not support lateral join column parameters - cannot use column "title" in this context. InternalError: Binder Error: Function "query" is a table function but it was used as a scalar function. This function has to be called in a FROM clause (similar to a table). InternalError: Catalog Error: Table with name nope does not exist! ``` ## Similar functions | Function | What it takes | Example | | --- | --- | --- | | [query_table](/develop/docs/dev-database-reference-sql-functions-table-functions-query-table) | A table name, or a list of names | `query_table('"<bucket>/<schema>".articles')` | | A plain `SELECT` | The statement itself | `SELECT id, title FROM articles WHERE id = 2` | The same row three ways: ``` run(f"SELECT * FROM query('SELECT id, title FROM {TABLE} WHERE id = 2')") run(f"SELECT id, title FROM query_table('{TABLE}') WHERE id = 2") run(f"SELECT id, title FROM {TABLE} WHERE id = 2") ``` ``` [(2, 'Vector search')] [(2, 'Vector search')] [(2, 'Vector search')] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Table functions](/develop/docs/dev-database-reference-sql-functions-table-functions): all the table functions. - [query_table](/develop/docs/dev-database-reference-sql-functions-table-functions-query-table): read a table named in a string. - [SELECT](/develop/docs/dev-database-reference-sql-select) and [EXPLAIN](/develop/docs/dev-database-reference-sql-explain): how to read a plan.