--- title: "split_part" slug: "dev-database-reference-sql-functions-string-split-part" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-string-split-part" --- > ## 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. # split_part *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Search and split](/develop/docs/dev-database-reference-sql-functions-string-search-and-split) › Search and split.* Splits a string on a separator and returns one field: `split_part('a,b,c', ',', 2)` is `'b'`. Fields count from 1; a negative position counts from the end. A field that doesn't exist gives an empty string, not `NULL`. ## Syntax ``` split_part(s, separator, n) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | The string to split. | | `separator` | `VARCHAR` | The text between fields. It can be longer than one character; it's matched exactly, with case. An empty separator splits into single characters. | | `n` | An integer | The field to return. `1` is the first field, `-1` the last. | **Returns:** `VARCHAR`. ## 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_split_part`. 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 log files, each with a path, an owner's email address and a comma-separated list of tags. 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_string_split_part"' 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}.logs" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, path VARCHAR, owner VARCHAR, tags VARCHAR)") run(f"INSERT INTO {TABLE} VALUES " "(1, '/var/log/app/server.log', 'ada@example.com', 'prod,web'), " "(2, '/var/log/db/query.log', 'grace@example.org', 'prod,db,eu'), " "(3, '/tmp/debug.log', 'jos\u00e9@example.co.uk', 'dev,,local'), " "(4, NULL, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `split_part(s, separator, n)` cuts `s` at every occurrence of `separator` and returns field `n`: | Call | Result | | --- | --- | | `split_part('a,b,c', ',', 1)` | `'a'` | | `split_part('a,b,c', ',', 3)` | `'c'` | | `split_part('a,b,c', ',', -1)` | `'c'`: the last field | | `split_part('a,b,c', ',', -3)` | `'a'` | | `split_part('a::b::c', '::', 2)` | `'b'` | | `split_part('a, b', ', ', 2)` | `'b'` | | `split_part('abc', '', 2)` | `'b'`: an empty separator makes each character a field | A path that starts with the separator has an empty first field: in `'/var/log/app'` split on `'/'`, field 1 is `''` and field 2 is `'var'`. ## NULLs and edge cases | Input | Result | | --- | --- | | Any argument `NULL` | `NULL` | | `n` = 0 | `''` | | `n` past the last field, from either end (`4` or `-4` for `'a,b,c'`) | `''` | | `n` = 9223372036854775807 | `''` | | An empty field (`'a,,c'`, field 2) | `''` | | The separator isn't in `s` | Field 1 is all of `s`; field 2 is `''` | | `''` (empty string) | `''` | | `split_part('A,b', 'a', 1)` | `'A,b'`: the separator is matched with case | | `split_part('é,ü', ',', 2)` | `'ü'` | | `n` = 1.7 | Error: `No function matches the given name and argument types 'array_extract(VARCHAR[], DECIMAL(2,1))'` | 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-string-split-part#set-up-the-examples): ``` run("SELECT split_part(NULL, ',', 2), split_part('a,b', NULL, 1), split_part('a,b', ',', NULL)") run("SELECT split_part('a,b,c', ',', 0), split_part('a,b,c', ',', 4), split_part('a,b,c', ',', -4), split_part('a,b', ',', 9223372036854775807)") run("SELECT split_part('a,,c', ',', 2), split_part('a,b', 'x', 1), split_part('a,b', 'x', 2), split_part('', ',', 1)") run("SELECT split_part('A,b', 'a', 1), split_part('\u00e9,\u00fc', ',', 2)") run("SELECT split_part('a,b', ',', 1.7)") ``` ``` [(None, None, None)] [('', '', '', '')] [('', 'a,b', '', '')] [('A,b', 'ü')] InternalError: Binder Error: No function matches the given name and argument types 'array_extract(VARCHAR[], DECIMAL(2,1))'. You might need to add explicit type casts. ``` ## Examples The directory under `/var/log`, the owner's domain (the last field after `@`) and the third tag of each file: ``` run(f"SELECT id, split_part(path, '/', 4), split_part(owner, '@', -1), split_part(tags, ',', 3) " f"FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 'app', 'example.com', ''), (2, 'db', 'example.org', 'eu'), (3, '', 'example.co.uk', 'local'), (4, None, None, None)] ``` The files whose first tag is `prod`: ``` run(f"SELECT id, path FROM {TABLE} WHERE split_part(tags, ',', 1) = 'prod' ORDER BY id LIMIT 10") ``` ``` [(1, '/var/log/app/server.log'), (2, '/var/log/db/query.log')] ``` ## 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 `split_part()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `split_part()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `split_part()` 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 split_part(tags, ',', 1) = 'prod'") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (CASE WHEN ((tags IS NOT │ │ NULL)) THEN (COALESCE │ │ (array_extract │ │ (string_split(tags, ','), │ │ 1), '')) ELSE NULL END = │ │ 'prod') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ tags │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store the fields you filter on.** If you often split a column to filter on one field, write that field to its own column when you load the data. A comparison of the raw column with a constant is pushed down to VAST DataBase, so rows that don't match never leave storage. The plan for `owner = 'ada@example.com'` has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE owner = 'ada@example.com'") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Combine it with a pushed-down condition.** In `id > 100 AND split_part(tags, ',', 1) = 'prod'`, `id > 100` is still evaluated in VAST DataBase, so `split_part()` runs only on the rows that pass it. ## Limitations and errors - **Strings only.** A number, date, list or `BLOB` fails with an error that names `string_split`, which `split_part` calls: for example `No function matches the given name and argument types 'string_split(INTEGER_LITERAL, STRING_LITERAL)'`. Cast the value to `VARCHAR` first. - **`n` must be an integer.** A decimal fails with the `array_extract` error shown above. - **An empty string, not `NULL`, for a missing field.** Test with `= ''`, or use `NULLIF(split_part(s, sep, n), '')` to turn it into `NULL`. - **The separator is plain text.** For a regular expression, use [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array). ``` run("SELECT split_part(123, ',', 2)") run("SELECT split_part(CAST(123 AS VARCHAR), '2', 2), NULLIF(split_part('a,b', ',', 3), '')") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'string_split(INTEGER_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. [('3', None)] ``` ## Similar functions | Function | Returns | `'a,b,c'` on `','`, field 2 | Field 5 | | --- | --- | --- | --- | | `split_part(s, sep, n)` | one field as `VARCHAR` | `'b'` | `''` | | [string_split](/develop/docs/dev-database-reference-sql-functions-string-string-split)`(s, sep)[n]`, also `str_split` | a list of all the fields, indexed | `'b'` | `NULL` | | [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array) | a list, split on a regular expression | | | ``` run("SELECT split_part('a,b,c', ',', 2), string_split('a,b,c', ',')[2], str_split('a,b,c', ',')[2]") run("SELECT split_part('a,b,c', ',', 5), string_split('a,b,c', ',')[5]") ``` ``` [('b', 'b', 'b')] [('', None)] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Search and split](/develop/docs/dev-database-reference-sql-functions-string-search-and-split): all the search and split functions. - [string_split](/develop/docs/dev-database-reference-sql-functions-string-string-split) and [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array). - [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.