--- title: "length_grapheme" slug: "dev-database-reference-sql-functions-string-length-grapheme" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-string-length-grapheme" --- > ## 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. # length_grapheme *Applies to VAST Cluster 5.5.* *[Functions](/develop/docs/dev-database-reference-sql-functions-index) › [Text basics](/develop/docs/dev-database-reference-sql-functions-string-text-basics) › Length.* Returns the number of grapheme clusters in a string: the characters a reader sees, so a letter with a combining accent or an emoji made of several code points counts as one. It has no aliases. ## Syntax ``` length_grapheme(s) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | The string to measure. | **Returns:** `BIGINT`. **Aliases:** none. ## 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_length_grapheme`. 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 five short posts. Post 2 has an accent written as a combining mark, post 3 a flag and post 4 a family emoji. 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_length_grapheme"' 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}.posts" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, author VARCHAR, body VARCHAR)") run(f"INSERT INTO {TABLE} VALUES " "(1, 'ada', 'Hello'), " "(2, 'jose', 'Cafe\u0301 au lait'), " "(3, 'marie', 'Bonjour 🇫🇷'), " "(4, 'kim', '\U0001F468\u200D\U0001F469\u200D\U0001F467 at home'), " "(5, NULL, NULL)") ``` ``` [] [] [(5,)] ``` ## What it does A string is a sequence of Unicode code points, and [length](/develop/docs/dev-database-reference-sql-functions-string-length) counts those. But some of what a reader sees as one character is made of several code points: - **A letter and combining marks.** é can be one code point (U+00E9) or two: `e` followed by the combining acute accent U+0301. Both look the same. - **Flags.** A flag emoji is two regional-indicator code points: 🇫🇷 is the indicators for F and R. - **Emoji sequences.** 👨‍👩‍👧 is three emoji joined by two zero-width joiners (U+200D): five code points. Unicode calls each of these visible units a *grapheme cluster*. `length_grapheme` counts grapheme clusters: | Input | `length` (code points) | `length_grapheme` | | --- | --- | --- | | `'café'` (é as U+00E9) | `4` | `4` | | `'e\u0301'` (e and a combining accent) | `2` | `1` | | `'🇫🇷'` | `2` | `1` | | `'\U0001F468\u200D\U0001F469\u200D\U0001F467'` (👨‍👩‍👧) | `5` | `1` | | `'e\u0301 🇫🇷 ẞ'` | `7` | `5` | It works on long strings too: 100,000 copies of `e` followed by U+0301 count as 100,000. Use it when a limit or a layout is about what people see, such as a display width or a character limit on a message. For storage limits, count bytes with [strlen](/develop/docs/dev-database-reference-sql-functions-string-strlen). A carriage return followed by a line feed (`'\r\n'`) counts as two. ## NULLs and edge cases | Input | Result | | --- | --- | | `NULL` | `NULL` | | `''` (empty string) | `0` | | `'e\u0301'` (e and a combining accent) | `1` | | `'🇫🇷'` (a flag emoji) | `1` | | `'\U0001F468\u200D\U0001F469\u200D\U0001F467'` (a family emoji) | `1` (`length` gives `5`) | | `'\r\n'` (carriage return and line feed) | `2` (`length` gives `2` too) | | `'e\u0301 🇫🇷 ẞ'` | `5` (`length` gives `7`) | | A `BLOB` | Error: `No function matches the given name and argument types 'length_grapheme(BLOB)'` | | A list, such as `['a', 'b']` | Error: `No function matches the given name and argument types 'length_grapheme(VARCHAR[])'` | | A number, date or boolean | Error: `No function matches the given name and argument types`, for example `'length_grapheme(INTEGER_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-string-length-grapheme#set-up-the-examples): ``` run("SELECT length_grapheme(NULL), length_grapheme(''), length_grapheme('e\u0301'), length_grapheme('🇫🇷')") run("SELECT length_grapheme('\U0001F468\u200D\U0001F469\u200D\U0001F467'), length_grapheme('\r\n'), length('\r\n')") run("SELECT length('\U0001F468\u200D\U0001F469\u200D\U0001F467'), length('e\u0301 🇫🇷 ẞ'), length_grapheme('e\u0301 🇫🇷 ẞ')") run("SELECT length_grapheme('\\xAA'::BLOB)") run("SELECT length_grapheme(['a', 'b'])") run("SELECT length_grapheme(123)") ``` ``` [(None, 0, 1, 1)] [(1, 2, 2)] [(5, 7, 5)] InternalError: Binder Error: No function matches the given name and argument types 'length_grapheme(BLOB)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'length_grapheme(VARCHAR[])'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'length_grapheme(INTEGER_LITERAL)'. You might need to add explicit type casts. ``` ## Examples Code points and grapheme clusters for each post. They differ for posts 2, 3 and 4: ``` run(f"SELECT id, length(body), length_grapheme(body) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 5, 5), (2, 13, 12), (3, 10, 9), (4, 13, 9), (5, None, None)] ``` Find the posts with combining marks, flags or emoji sequences: the ones where the two counts differ: ``` run(f"SELECT id, author FROM {TABLE} WHERE length(body) <> length_grapheme(body) ORDER BY id LIMIT 10") ``` ``` [(2, 'jose'), (3, 'marie'), (4, 'kim')] ``` Apply a limit of 9 visible characters. Posts 3 and 4 fit: each has 9 grapheme clusters, but 10 and 13 code points, so the same limit on `length` would reject them: ``` run(f"SELECT id, author FROM {TABLE} WHERE length_grapheme(body) <= 9 ORDER BY id LIMIT 10") ``` ``` [(1, 'ada'), (3, 'marie'), (4, 'kim')] ``` ## 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 `length_grapheme()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `length_grapheme()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `length_grapheme()` and keeps the rows that match. No rows are skipped in storage. The plan of the limit example shows the `FILTER` step above the scan: ``` plan(f"SELECT id FROM {TABLE} WHERE length_grapheme(body) <= 9") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (length_grapheme(body) <= │ │ 9) │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ body │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Test for empty strings with `= ''`, not `length_grapheme(s) = 0`.** 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 `body = ''` has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE body = ''") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Store the count if you filter on it often.** Compute it when you write the rows and keep it in its own column: `body_chars <= 9` is pushed down, `length_grapheme(body) <= 9` isn't. - **Combine it with a pushed-down condition.** In `id > 2 AND length_grapheme(body) <= 9`, `id > 2` is still evaluated in VAST DataBase, so `length_grapheme()` runs only on the rows that pass it. ## Limitations and errors - **Strings only.** A number, a date, a boolean, a list or a `BLOB` fails with `No function matches the given name and argument types`; the error lists `length_grapheme(VARCHAR)` as the only form. For the elements of a list, use [length](/develop/docs/dev-database-reference-sql-functions-string-length). - **`\r\n` is two.** A carriage return and line feed pair counts as two grapheme clusters. If line endings matter to a limit, replace `'\r\n'` with `'\n'` first. ``` run("SELECT length_grapheme([1, 2])") run("SELECT length_grapheme(replace('a\r\nb', '\r\n', '\n'))") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'length_grapheme(INTEGER[])'. You might need to add explicit type casts. [(3,)] ``` ## Similar functions | Function | What it does | Result for `'e\u0301x'` (e, a combining accent, x; `length_grapheme` gives `2`) | | --- | --- | --- | | [length](/develop/docs/dev-database-reference-sql-functions-string-length) | counts code points | `3` | | [strlen](/develop/docs/dev-database-reference-sql-functions-string-strlen) | counts bytes in UTF-8 | `4` | | [left_grapheme](/develop/docs/dev-database-reference-sql-functions-string-left-grapheme) | the first *n* grapheme clusters | `left_grapheme(s, 1)` gives `e` and the accent | | [left](/develop/docs/dev-database-reference-sql-functions-string-left) | the first *n* code points | `left(s, 1)` gives `e`, without the accent | | [substring_grapheme](/develop/docs/dev-database-reference-sql-functions-string-substring-grapheme) | part of a string, counted in grapheme clusters | `substring_grapheme(s, 1, 1)` gives `e` and the accent | | [right_grapheme](/develop/docs/dev-database-reference-sql-functions-string-right-grapheme) | the last *n* grapheme clusters | `right_grapheme(s, 1)` gives `x` | ``` run("SELECT length_grapheme('e\u0301x'), length('e\u0301x'), strlen('e\u0301x')") run("SELECT left_grapheme('e\u0301x', 1), left('e\u0301x', 1), substring_grapheme('e\u0301x', 1, 1), right_grapheme('e\u0301x', 1)") ``` ``` [(2, 3, 4)] [('é', 'e', 'é', 'x')] ``` Clean up: ``` run(f"DROP TABLE IF EXISTS {TABLE}") run(f"DROP SCHEMA IF EXISTS {SCHEMA}") conn.close() ``` ``` [] [] ``` ## See also - [Text basics](/develop/docs/dev-database-reference-sql-functions-string-text-basics): all the text functions. - [length](/develop/docs/dev-database-reference-sql-functions-string-length) and [strlen](/develop/docs/dev-database-reference-sql-functions-string-strlen): code points and bytes. - [left_grapheme](/develop/docs/dev-database-reference-sql-functions-string-left-grapheme), [right_grapheme](/develop/docs/dev-database-reference-sql-functions-string-right-grapheme) and [substring_grapheme](/develop/docs/dev-database-reference-sql-functions-string-substring-grapheme): cut a string without splitting what a reader sees as a character. - [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.