--- title: "getvariable" slug: "dev-database-reference-sql-functions-utility-getvariable" updated: 2026-10-30T18:18:51Z published: 2026-10-30T18:18:51Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-utility-getvariable" --- > ## 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. # getvariable *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Session and utility functions](/develop/docs/dev-database-reference-sql-functions-utility) › Session and diagnostics.* Returns the value of the variable with the given name, or `NULL` when the variable has no value. The name must be a constant string. ## Syntax ``` getvariable('name') ``` | Argument | Type | Description | | --- | --- | --- | | `name` | `VARCHAR` constant | The name of the variable. | **Returns:** the variable's type; `NULL` (of type `"NULL"`) when it has no value. ## 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_string_getvariable`. 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 small table that holds variable names, to show what happens when the name comes from a column: ``` 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_string_getvariable"' 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}.names" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, name VARCHAR)") run(f"INSERT INTO {TABLE} VALUES (1, 'v'), (2, 'w'), (3, NULL)") ``` ``` [] [] [(3,)] ``` ## What it does `getvariable(name)` looks up a variable by name. If the variable has no value, the result is `NULL`, and its type is `"NULL"`; no error is raised. The name must be a constant: a column fails. ## NULLs and edge cases | Input | Result | | --- | --- | | A name with no value, such as `'v'` | `NULL` | | `''` (empty string) | `NULL` | | `NULL` | `NULL` | | `typeof(getvariable('v'))` | `"NULL"` | | A column | Error: `getvariable requires a constant input` | | A number | Error: `No function matches the given name and argument types 'getvariable(INTEGER_LITERAL)'` | | Two arguments | Error: `No function matches the given name and argument types 'getvariable(STRING_LITERAL, STRING_LITERAL)'` | 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-utility-getvariable#set-up-the-examples): ``` run("SELECT getvariable('v'), getvariable(''), getvariable(NULL), typeof(getvariable('v'))") run(f"SELECT id, getvariable(name) FROM {TABLE} ORDER BY id LIMIT 10") run("SELECT getvariable(123)") run("SELECT getvariable('v', 'w')") ``` ``` [(None, None, None, '"NULL"')] InternalError: Not implemented Error: getvariable requires a constant input InternalError: Binder Error: No function matches the given name and argument types 'getvariable(INTEGER_LITERAL)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'getvariable(STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. ``` ## Examples Use a default when the variable has no value: ``` run("SELECT coalesce(getvariable('v'), 'not set'), getvariable('v') IS NULL") ``` ``` [('not set', True)] ``` Use it in a condition on a table. With no value, the comparison is `NULL`, so no row passes it: ``` run(f"SELECT id, name FROM {TABLE} WHERE name = getvariable('v') ORDER BY id LIMIT 10") ``` ``` [] ``` ## How it runs in VAST The Query Engine runs on the cluster's CNodes. `getvariable` reads a variable of the Query Engine, not data, and its name must be a constant: a column, in the `SELECT` list, in `WHERE` or in `EXPLAIN`, fails with `getvariable requires a constant input`. With no value, the condition can never be true, and the plan of the condition above has no scan: it's a single `EMPTY_RESULT` step. ``` plan(f"SELECT id FROM {TABLE} WHERE name = getvariable('v')") ``` ``` ┌───────────────────────────┐ │ EMPTY_RESULT │ └───────────────────────────┘ ``` ## Make it faster - **Nothing to tune for the call itself.** It takes only a constant name. What costs time is the rest of the query; see [pushdowns](/develop/docs/dev-database-reference-pushdowns). ## Limitations and errors - **The name must be a constant.** A column fails with `getvariable requires a constant input`. - **An unknown name isn't an error.** It returns `NULL`, the same as a variable with no value. Check for `NULL`, or give a default with [coalesce](/develop/docs/dev-database-reference-sql-functions-conditional-and-cast-coalesce). - **One argument only.** Two arguments fail with `No function matches the given name and argument types`. ## Similar functions | Function | Returns | For an unknown name | | --- | --- | --- | | `getvariable` | The value of a variable | `NULL` | | [current_setting](/develop/docs/dev-database-reference-sql-functions-utility-current-setting) | The value of a Query Engine setting | Error: `unrecognized configuration parameter` | ``` run("SELECT getvariable('no_such_name_xyz'), current_setting('default_order')") run("SELECT current_setting('no_such_name_xyz')") ``` ``` [(None, 'asc')] InternalError: Catalog Error: unrecognized configuration parameter "no_such_name_xyz" ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [current_setting](/develop/docs/dev-database-reference-sql-functions-utility-current-setting): read a Query Engine setting. - [Functions](/develop/docs/dev-database-reference-sql-functions-index): all the function families.