--- title: "string_split" slug: "dev-database-reference-sql-functions-string-string-split" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-string-string-split" --- > ## 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. # string_split *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) › Splitting.* Splits a string at every occurrence of a separator and returns the parts as a list (`VARCHAR[]`). The separator is literal text, not a pattern. `str_split`, `split` and `string_to_array` are the same function. ## Syntax ``` string_split(s, separator) str_split(s, separator) split(s, separator) string_to_array(s, separator) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | The string to split. | | `separator` | `VARCHAR` | The text between the parts. It can be longer than one character, and it's matched literally and case-sensitively. An empty separator splits into single code points. | **Returns:** `VARCHAR[]`, a list that the driver returns as a Python list. **Aliases:** `str_split`, `split`, `string_to_array`. ## 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_string_split`. 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 servers, each with a comma-separated list of tags and a file path. Row 2 has an empty tag between two commas, row 3 has no tags, and 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_string_split"' 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}.servers" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, tags VARCHAR, path VARCHAR)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'prod,web', '/data/logs/app.log'), " "(2, 'prod,db,,eu', '/data/db/main.db'), " "(3, '', '/tmp/x'), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `string_split(s, separator)` cuts the string at every occurrence of the separator, from left to right, and returns the pieces in order. Nothing is dropped: | Call | Result | | --- | --- | | `string_split('a,b,,c', ',')` | `['a', 'b', '', 'c']`: an empty part between two separators is kept | | `string_split(',a,', ',')` | `['', 'a', '']`: a separator at either end gives an empty part there | | `string_split('a b c', ' ')` | `['a', 'b', '', 'c']`: each space is one separator | | `string_split('a::b::c', '::')` | `['a', 'b', 'c']` | | `string_split('a.b', '.')`, `string_split('a\\|b', '\\|')` | `['a', 'b']`: `.` and `\\|` are literal, not patterns | | `string_split('aXbxc', 'x')` | `['aXb', 'c']`: the match is case-sensitive | | `string_split('abc', ',')` | `['abc']`: no separator, one part | | `string_split('abc', '')` | `['a', 'b', 'c']` | **An empty separator** splits the string into code points, not into what a reader sees as characters: a flag emoji becomes its two halves, and `e` followed by a combining accent becomes `e` and the accent alone. **The result is a list,** so the [list functions](/develop/docs/dev-database-reference-sql-functions-lists-and-structs) work on it: `[1]` takes the first part, `[-1]` the last, `[2:3]` the second and third, and `len()` counts the parts. A position past the end gives NULL. To split and take one part in one step, use [split_part](/develop/docs/dev-database-reference-sql-functions-string-split-part). ## NULLs and edge cases | Input | Result | | --- | --- | | `s` is NULL | `NULL` | | `separator` is NULL | the whole string as the only part: `['a,b']` | | `''` (empty string), with any separator | `['']`: one empty part, so `len()` is 1 | | `string_split('a,b', ',,')` (separator not found) | `['a,b']` | | `string_split('\U0001F1EB\U0001F1F7', '')` (a flag emoji) | its two code points | | `string_split('e\u0301', '')` (`e` and a combining accent) | `['e', '\u0301']` | | `string_split('a,b', ',')[5]` (past the end) | `NULL` | | `s` a number, date, boolean, `BLOB` or list, or a number as the separator | Error: `No function matches the given name and argument types` | | A third argument (a limit) | Error: `No function matches the given name and argument types` | 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-string-split#set-up-the-examples): ``` run("SELECT string_split(NULL, ','), string_split('a,b', NULL), string_split('', ','), len(string_split('', ',')), " "string_split('a,b', ',,')") run("SELECT string_split('a,b,,c', ','), string_split(',a,', ','), string_split('a b c', ' '), " "string_split('a::b::c', '::'), string_split('a.b', '.'), string_split('aXbxc', 'x')") run("SELECT string_split('abc', ''), string_split('\U0001F1EB\U0001F1F7', ''), string_split('e\u0301', '')") run("SELECT string_split('a,b,c', ',')[1], string_split('a,b,c', ',')[-1], string_split('a,b', ',')[5], " "string_split('a,b,c', ',')[2:3], len(string_split('a,b,c', ','))") run("SELECT string_split(123, ',')") run("SELECT string_split('a,b,c', ',', 2)") ``` ``` [(None, ['a,b'], [''], 1, ['a,b'])] [(['a', 'b', '', 'c'], ['', 'a', ''], ['a', 'b', '', 'c'], ['a', 'b', 'c'], ['a', 'b'], ['aXb', 'c'])] [(['a', 'b', 'c'], ['🇫', '🇷'], ['e', '́'])] [('a', 'c', None, ['b', 'c'], 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. InternalError: Binder Error: No function matches the given name and argument types 'string_split(STRING_LITERAL, STRING_LITERAL, INTEGER_LITERAL)'. You might need to add explicit type casts. ``` ## Examples The tags of each server as a list, how many there are, and the first one. Row 2 keeps its empty tag: ``` run(f"SELECT id, string_split(tags, ','), len(string_split(tags, ',')), string_split(tags, ',')[1] " f"FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, ['prod', 'web'], 2, 'prod'), (2, ['prod', 'db', '', 'eu'], 4, 'prod'), (3, [''], 1, ''), (4, None, None, None)] ``` The four names are the same function. A path that starts with `/` gives an empty first part: ``` run(f"SELECT string_split(path, '/'), str_split(path, '/'), split(path, '/'), string_to_array(path, '/') " f"FROM {TABLE} WHERE id = 1 LIMIT 10") ``` ``` [(['', 'data', 'logs', 'app.log'], ['', 'data', 'logs', 'app.log'], ['', 'data', 'logs', 'app.log'], ['', 'data', 'logs', 'app.log'])] ``` Keep the servers tagged `db`, and get one row for each tag with [unnest](/develop/docs/dev-database-reference-sql-functions-table-functions-unnest). The other columns repeat on each row: ``` run(f"SELECT id, tags FROM {TABLE} WHERE list_contains(string_split(tags, ','), 'db') ORDER BY id LIMIT 10") run(f"SELECT id, unnest(string_split(tags, ',')) AS tag FROM {TABLE} WHERE id = 1 LIMIT 10") ``` ``` [(2, 'prod,db,,eu')] [(1, 'prod'), (1, 'web')] ``` ## 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 `string_split()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine splits it for each row it returns. - **In `WHERE`,** for example inside `list_contains()`, the scan sends the column for every row, and a `FILTER` step in the Query Engine splits it and keeps the rows that match. No rows are skipped in storage. The plan of the `list_contains()` example shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE list_contains(string_split(tags, ','), 'db')") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ list_contains(string_split│ │ (tags, ','), 'db') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ tags │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Filter on a prefix with a range.** To find paths under `/data/`, `path >= '/data/' AND path < '/data0'` is pushed down to VAST DataBase, so rows that don't match never leave storage; `string_split(path, '/')[2] = 'data'` isn't. (`0` is the character after `/`.) The plan of the range has no `FILTER` step. - **Store lists as lists.** If you often search a delimited string, write it as a `VARCHAR[]` column, or as one row per value, when you load the data, so queries don't split it every time. - **`split_part` costs the same.** [split_part](/develop/docs/dev-database-reference-sql-functions-string-split-part) is planned as `string_split()` followed by taking one element, so choose whichever reads better; neither is pushed down. ``` plan(f"SELECT id FROM {TABLE} WHERE path >= '/data/' AND path < '/data0'") run(f"SELECT id FROM {TABLE} WHERE path >= '/data/' AND path < '/data0' ORDER BY id LIMIT 10") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ [(1,), (2,)] ``` ## Limitations and errors - **`VARCHAR` only.** A number, a date, a boolean, a `BLOB` or a list fails with `No function matches the given name and argument types 'string_split(INTEGER_LITERAL, STRING_LITERAL)'` (with the type you passed). Cast it first: `string_split(CAST(n AS VARCHAR), '0')`. - **No limit argument.** `string_split(s, sep, 2)` fails with `No function matches the given name and argument types 'string_split(STRING_LITERAL, STRING_LITERAL, INTEGER_LITERAL)'`. Take the parts you need with a slice, such as `[1:2]`. - **A literal separator only.** To split on a pattern, such as any run of spaces or several separator characters, use [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array). - **No `split_to_table`.** It fails with `Scalar Function with name split_to_table does not exist!`. Use `unnest(string_split(s, sep))`, as in [Examples](/develop/docs/dev-database-reference-sql-functions-string-string-split#examples). ``` run("SELECT string_split(CAST(10203 AS VARCHAR), '0'), string_split('a,b,c', ',')[1:2]") run("SELECT split_to_table('a,b', ',')") ``` ``` [(['1', '2', '3'], ['a', 'b'])] InternalError: Catalog Error: Scalar Function with name split_to_table does not exist! ``` ## Similar functions | Function | Splits on | Returns | Result for `'a,b,,c'` and `','` | | --- | --- | --- | --- | | `string_split(s, sep)` | literal text | a list | `['a', 'b', '', 'c']` | | [split_part](/develop/docs/dev-database-reference-sql-functions-string-split-part) `(s, sep, 2)` | literal text | one part | `'b'` | | [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array) `(s, ',')` | a regular expression | a list | `['a', 'b', '', 'c']` | | [regexp_split_to_table](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-table) `(s, ',')` | a regular expression | one row for each part | | | [regexp_extract_all](/develop/docs/dev-database-reference-sql-functions-string-regexp-extract-all) `(s, '[^,]+')` | the parts that match | a list | `['a', 'b', 'c']` | The separator `.` is literal for `string_split` and a pattern for `regexp_split_to_array`: ``` run("SELECT string_split('a,b,,c', ','), split_part('a,b,,c', ',', 2), regexp_split_to_array('a,b,,c', ','), " "regexp_extract_all('a,b,,c', '[^,]+')") run("SELECT string_split('a.b', '.'), regexp_split_to_array('a.b', '.'), regexp_split_to_array('a.b', '\\.')") ``` ``` [(['a', 'b', '', 'c'], 'b', ['a', 'b', '', 'c'], ['a', 'b', 'c'])] [(['a', 'b'], ['', '', '', ''], ['a', 'b'])] ``` 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. - [split_part](/develop/docs/dev-database-reference-sql-functions-string-split-part), [regexp_split_to_array](/develop/docs/dev-database-reference-sql-functions-string-regexp-split-to-array) and [unnest](/develop/docs/dev-database-reference-sql-functions-table-functions-unnest). - [List functions](/develop/docs/dev-database-reference-sql-functions-lists-and-structs), such as [list_contains](/develop/docs/dev-database-reference-sql-functions-lists-list-contains) and [array_to_string](/develop/docs/dev-database-reference-sql-functions-lists-array-to-string). - [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.