--- title: "right_grapheme" slug: "dev-database-reference-sql-functions-string-right-grapheme" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-string-right-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. # right_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) › Parts of a string.* Returns the last `n` characters of a string as a reader sees them (grapheme clusters); with a negative `n`, everything except the first `-n`. There are no aliases. ## Syntax ``` right_grapheme(s, n) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | The string to take characters from. | | `n` | `BIGINT` (any integer) | How many grapheme clusters to keep, counted from the end. A negative `n` drops `-n` grapheme clusters from the start instead. | **Returns:** `VARCHAR`. **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_right_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 four posts. One author's name ends in a combining accent, and the posts end with a flag, a combining accent and a plain letter; 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_right_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, 'Grace', 'Greetings from New York \U0001F1FA\U0001F1F8'), " "(2, 'Jose\u0301', 'Lunch at the cafe\u0301'), " "(3, 'Ada', 'Hello from London'), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `right_grapheme` works like [right](/develop/docs/dev-database-reference-sql-functions-string-right), but counts grapheme clusters instead of code points. A **code point** is one Unicode value: the unit [length](/develop/docs/dev-database-reference-sql-functions-string-length), [right](/develop/docs/dev-database-reference-sql-functions-string-right) and [substring](/develop/docs/dev-database-reference-sql-functions-string-substring) count. A **grapheme cluster** is what a reader sees as one character, and it can be several code points. A combining accent comes *after* its letter, so the end of a string is where `right` cuts it off: | What the reader sees | Code points | `right(…, 1)` | `right_grapheme(…, 1)` | | --- | --- | --- | --- | | café, written with `e` and a combining accent (`'cafe\u0301'`) | 2 for the é | the accent U+0301 alone | `'e\u0301'` (é) | | The US flag 🇺🇸 at the end of `'New York 🇺🇸'` | 2 for the flag: two regional-indicator letters | half a flag | `'🇺🇸'` | | A letter such as `o` in `'Hello'` | 1 | `'o'` | `'o'` | An emoji made of several emoji joined by zero-width joiners, such as a family, is also one grapheme cluster ([length_grapheme](/develop/docs/dev-database-reference-sql-functions-string-length-grapheme) counts it as 1). So `right_grapheme` never returns half a character. The count follows the same rules as `right`: | `n` | What you get | Example | Result | | --- | --- | --- | --- | | Positive | the last `n` grapheme clusters | `right_grapheme('cafe\u0301', 1)` | `'e\u0301'` (é) | | Larger than the string | the whole string | `right_grapheme('abc', 10)` | `'abc'` | | `0` | an empty string | `right_grapheme('abc', 0)` | `''` | | Negative | all but the first `-n` grapheme clusters | `right_grapheme('abc', -1)` | `'bc'` | ## NULLs and edge cases | Input | Result | | --- | --- | | `s` is NULL | `NULL` | | `n` is NULL | `NULL` | | `''` (empty string) | `''` | | `right_grapheme('abc', -1)` | `'bc'` | | `right_grapheme('abc', 10)` | `'abc'` | | `right_grapheme('abc', 0)` | `''` | | `right_grapheme('cafe\u0301', 1)` (café with a combining accent) | `'e\u0301'` (é, both code points) | | `s` a number, date, boolean, `BLOB` or list | 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-right-grapheme#set-up-the-examples). `length()` of the result shows that both code points of the é are kept: ``` run("SELECT right_grapheme(NULL, 1), right_grapheme('abc', NULL), right_grapheme('', 1), " "right_grapheme('abc', -1), right_grapheme('abc', 10), right_grapheme('abc', 0)") run("SELECT right_grapheme('cafe\u0301', 1), length(right_grapheme('cafe\u0301', 1))") run("SELECT right_grapheme(123, 1)") ``` ``` [(None, None, '', 'bc', 'abc', '')] [('é', 2)] InternalError: Binder Error: No function matches the given name and argument types 'right_grapheme(INTEGER_LITERAL, INTEGER_LITERAL)'. You might need to add explicit type casts. ``` ## Examples The last character of each author's name and of each post, counted both ways. `right` returns the accent of `José` and `café` without its letter, and half of the flag; `right_grapheme` keeps them whole: ``` run(f"SELECT id, right(author, 1), right_grapheme(author, 1), right(body, 1), right_grapheme(body, 1) " f"FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, 'e', 'e', '🇸', '🇺🇸'), (2, '́', 'é', '́', 'é'), (3, 'a', 'a', 'n', 'n'), (4, None, None, None, None)] ``` Drop the first word of each post and the space after it with a negative count. `Greetings` and `Lunch` have ten and six grapheme clusters: ``` run(f"SELECT id, right_grapheme(body, -10) FROM {TABLE} WHERE id = 1") run(f"SELECT id, right_grapheme(body, -6) FROM {TABLE} WHERE id = 2") ``` ``` [(1, 'from New York 🇺🇸')] [(2, 'at the café')] ``` Keep only the posts that end with the US flag: ``` run(f"SELECT id FROM {TABLE} WHERE right_grapheme(body, 1) = '\U0001F1FA\U0001F1F8' ORDER BY id LIMIT 10") ``` ``` [(1,)] ``` ## 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 `right_grapheme()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `right_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 `right_grapheme()` 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 right_grapheme(body, 1) = '\U0001F1FA\U0001F1F8'") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ (right_grapheme(body, 1) =│ │ '🇺🇸') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ body │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Use `right` when the text is ASCII.** For text with no accents, emoji or other multi-code-point characters, such as codes and identifiers, a code point is a grapheme cluster, and [right](/develop/docs/dev-database-reference-sql-functions-string-right) gives the same result. - **Store what you filter on.** If you often filter on the last character, keep it in its own column when you write the rows: a comparison of a raw column with a constant is pushed down to VAST DataBase, so rows that don't match never leave storage. The plan has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE author = 'Grace'") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Combine it with a pushed-down condition.** In `id > 100 AND right_grapheme(body, 1) = '🇺🇸'`, `id > 100` is still evaluated in VAST DataBase, so `right_grapheme()` runs only on the rows that pass it. ## 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`. Cast a value to text first: `right_grapheme(CAST(n AS VARCHAR), 1)`. - **The count must be an integer.** A `DECIMAL` such as `2.7` fails with `No function matches the given name and argument types 'right_grapheme(STRING_LITERAL, DECIMAL(2,1))'`; it isn't converted for you. Cast it to an integer first: `right_grapheme(s, CAST(x AS BIGINT))`. The cast rounds, it doesn't truncate. - **Grapheme clusters, not normalised text.** `right_grapheme` keeps the code points it finds: a decomposed é (`e` and U+0301) comes back as two code points, as the `length()` in [NULLs and edge cases](/develop/docs/dev-database-reference-sql-functions-string-right-grapheme#nulls-and-edge-cases) shows. [nfc_normalize](/develop/docs/dev-database-reference-sql-functions-string-nfc-normalize) turns it into the one-code-point `é`. ``` run("SELECT right_grapheme(123, 1)") run("SELECT right_grapheme(CAST(123 AS VARCHAR), 1)") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'right_grapheme(INTEGER_LITERAL, INTEGER_LITERAL)'. You might need to add explicit type casts. [('3',)] ``` ## Similar functions | Function | Takes | Result for `'cafe\u0301'` (café) and 1 | | --- | --- | --- | | `right_grapheme(s, n)` | the last `n` grapheme clusters | `'e\u0301'` (é) | | [right](/develop/docs/dev-database-reference-sql-functions-string-right) | the last `n` code points | the accent U+0301 alone | | [substring_grapheme](/develop/docs/dev-database-reference-sql-functions-string-substring-grapheme) `(s, -n)` | grapheme clusters from the `n`th from the end | `'e\u0301'` (é) | | [substring](/develop/docs/dev-database-reference-sql-functions-string-substring) `(s, -n)` | code points from the `n`th from the end | the accent U+0301 alone | | [left_grapheme](/develop/docs/dev-database-reference-sql-functions-string-left-grapheme) | the first `n` grapheme clusters | | | [length_grapheme](/develop/docs/dev-database-reference-sql-functions-string-length-grapheme) | counts the grapheme clusters | | `length()` of each result shows how many code points it kept: ``` run("SELECT right_grapheme('cafe\u0301', 1), right('cafe\u0301', 1), substring_grapheme('cafe\u0301', -1), " "substring('cafe\u0301', -1)") run("SELECT length(right_grapheme('cafe\u0301', 1)), length(right('cafe\u0301', 1)), " "length(substring_grapheme('cafe\u0301', -1)), length(substring('cafe\u0301', -1))") ``` ``` [('é', '́', 'é', '́')] [(2, 1, 2, 1)] ``` 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. - [right](/develop/docs/dev-database-reference-sql-functions-string-right), [left_grapheme](/develop/docs/dev-database-reference-sql-functions-string-left-grapheme), [substring_grapheme](/develop/docs/dev-database-reference-sql-functions-string-substring-grapheme) and [length_grapheme](/develop/docs/dev-database-reference-sql-functions-string-length-grapheme). - [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.