--- title: "replace" slug: "dev-database-reference-sql-functions-string-replace" updated: 2026-10-30T18:18:56Z published: 2026-10-30T18:18:56Z canonical: "docs.vastdata.com/dev-database-reference-sql-functions-string-replace" --- > ## 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. # replace *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) › Changing text.* Replaces every occurrence of one substring with another. The match is exact and case-sensitive, with no patterns. `replace` has no aliases. ## Syntax ``` replace(s, source, target) ``` | Argument | Type | Description | | --- | --- | --- | | `s` | `VARCHAR` | The string to change. | | `source` | `VARCHAR` | The substring to look for. An empty string matches nothing. | | `target` | `VARCHAR` | The string to put in its place. An empty string deletes each match. | **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_replace`. 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 files: two Linux paths, a Windows path and a row with 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_replace"' 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}.files" run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}") run(f"CREATE TABLE IF NOT EXISTS {TABLE} (id BIGINT, path VARCHAR, title VARCHAR)") run(f"INSERT INTO {TABLE} VALUES " "(1, '/home/ada/notes.txt', 'Notes on the Analytical Engine'), " "(2, '/home/grace/compiler.tar.gz', 'The A-0 compiler'), " "(3, 'C:\\Users\\jose\\poems.docx', 'Versos sencillos'), " "(4, NULL, NULL)") ``` ``` [] [] [(4,)] ``` ## What it does `replace` scans `s` from left to right and replaces each occurrence of `source` with `target`. After a match, the scan continues after the matched text, so matches don't overlap: in `'aaa'`, `'aa'` matches once, at the start, and the last `a` is left as it is. | Call | Result | Why | | --- | --- | --- | | `replace('a.b.c', '.', '/')` | `'a/b/c'` | Every occurrence is replaced. `.` is an ordinary character, not a pattern. | | `replace('aaa', 'aa', 'b')` | `'ba'` | Matches don't overlap. | | `replace('aaa', 'a', '')` | `''` | An empty `target` deletes each match. | | `replace('abc', '', 'x')` | `'abc'` | An empty `source` matches nothing: the string is returned unchanged. | | `replace('Abc', 'a', 'x')` | `'Abc'` | The match is case-sensitive. | | `replace('café', 'é', 'e')` | `'cafe'` | Characters outside ASCII are matched like any other, when both are written the same way (here a precomposed `é`, U+00E9). | | `replace('abc', 'abc', '')` | `''` | Replacing the whole string with `''` gives an empty string, not `NULL`. | The match compares code points, not what the text looks like. `é` can be stored as one code point (U+00E9) or as `e` followed by U+0301, and the two don't match each other: replacing a precomposed `é` in `'cafe'` followed by U+0301 returns the string unchanged. If your data mixes the two forms, normalise both sides first with [nfc_normalize](/develop/docs/dev-database-reference-sql-functions-string-nfc-normalize). To replace a pattern rather than a fixed substring, use [regexp_replace](/develop/docs/dev-database-reference-sql-functions-string-regexp-replace). To replace single characters with other single characters, use [translate](/develop/docs/dev-database-reference-sql-functions-string-translate). ## NULLs and edge cases | Input | Call | Result | | --- | --- | --- | | `s` is `NULL` | `replace(NULL, 'l', 'L')` | `NULL` | | `source` is `NULL` | `replace('abc', NULL, 'x')` | `NULL` | | `target` is `NULL` | `replace('abc', 'a', NULL)` | `NULL` | | `''` (empty string) | `replace('', 'l', 'L')` | `''` | | Overlapping matches | `replace('aaa', 'aa', 'b')` | `'ba'` | | `source` is `''` | `replace('abc', '', 'x')` | `'abc'`, unchanged | | `target` is `''` | `replace('aaa', 'a', '')` | `''`: every match removed | | Different case | `replace('Abc', 'a', 'x')` | `'Abc'`, unchanged | | `.` in `source` | `replace('a.b.c', '.', '/')` | `'a/b/c'` | | A character outside ASCII | `replace('café', 'é', 'e')` | `'cafe'` | | A number as `s` | `replace(123, 'l', 'L')` | Error: `No function matches the given name and argument types` | | A `BLOB` as `s` | `replace('\xAA'::BLOB, 'l', 'L')` | 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-replace#set-up-the-examples): ``` run("SELECT replace(NULL, 'l', 'L'), replace('abc', NULL, 'x'), replace('abc', 'a', NULL), replace('', 'l', 'L')") run("SELECT replace('aaa', 'aa', 'b'), replace('abc', '', 'x'), replace('aaa', 'a', ''), replace('Abc', 'a', 'x'), replace('a.b.c', '.', '/'), replace('café', 'é', 'e')") run("SELECT replace(123, 'l', 'L')") run("SELECT replace('\\xAA'::BLOB, 'l', 'L')") ``` ``` [(None, None, None, '')] [('ba', 'abc', '', 'Abc', 'a/b/c', 'cafe')] InternalError: Binder Error: No function matches the given name and argument types 'replace(INTEGER_LITERAL, STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. InternalError: Binder Error: No function matches the given name and argument types 'replace(BLOB, STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. ``` ## Examples Move the files from `/home/` to `/users/`. The Windows path has no `/home/`, so it comes back unchanged: ``` run(f"SELECT id, replace(path, '/home/', '/users/') FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '/users/ada/notes.txt'), (2, '/users/grace/compiler.tar.gz'), (3, 'C:\\Users\\jose\\poems.docx'), (4, None)] ``` Nest calls to make several replacements. This turns each backslash into a slash, and each title into a lowercase slug with hyphens for spaces. In the Python string, `'\\'` is one backslash in SQL: ``` run(f"SELECT id, replace(path, '\\', '/'), lower(replace(title, ' ', '-')) FROM {TABLE} ORDER BY id LIMIT 10") ``` ``` [(1, '/home/ada/notes.txt', 'notes-on-the-analytical-engine'), (2, '/home/grace/compiler.tar.gz', 'the-a-0-compiler'), (3, 'C:/Users/jose/poems.docx', 'versos-sencillos'), (4, None, None)] ``` Find a file by its path with slashes, whichever separator it was stored with: ``` run(f"SELECT id, path FROM {TABLE} WHERE replace(path, '\\', '/') = 'C:/Users/jose/poems.docx' ORDER BY id LIMIT 10") ``` ``` [(3, 'C:\\Users\\jose\\poems.docx')] ``` ## 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 `replace()` is always computed by the Query Engine: - **In the `SELECT` list,** the scan reads the column and the Query Engine computes `replace()` for each row it returns. - **In `WHERE`,** the scan sends the column for every row, and a `FILTER` step in the Query Engine computes `replace()` 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 replace(path, '\\', '/') = 'C:/Users/jose/poems.docx'") ``` ``` ┌───────────────────────────┐ │ PROJECTION │ │ ──────────────────── │ │ #1 │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ FILTER │ │ ──────────────────── │ │ ("replace"(path, '\', '/')│ │ = 'C:/Users/jose/poems │ │ .docx') │ │ │ └─────────────┬─────────────┘ ┌─────────────┴─────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ │ │ Projections: │ │ path │ │ id │ │ │ └───────────────────────────┘ ``` ## Make it faster - **Store the normalised value if you filter on it often.** Apply `replace()` when you write the rows and keep the result in its own column. 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 `path = '/home/ada/notes.txt'` has no `FILTER` step: ``` plan(f"SELECT id FROM {TABLE} WHERE path = '/home/ada/notes.txt'") ``` ``` ┌───────────────────────────┐ │ VAST_SCAN │ │ ──────────────────── │ │ Function: VAST_SCAN │ │ Projections: id │ │ │ └───────────────────────────┘ ``` - **Combine it with a pushed-down condition.** In `id > 100 AND replace(path, '\', '/') = '...'`, `id > 100` is still evaluated in VAST DataBase, so `replace()` runs only on the rows that pass it. ## Limitations and errors - **Strings only.** A number, a decimal, a `BLOB`, a date, a boolean or a list fails with `No function matches the given name and argument types`. Cast a value to `VARCHAR` first: `replace(CAST(n AS VARCHAR), '2', '-')`. - **No patterns.** Every character in `source` is matched literally. Use [regexp_replace](/develop/docs/dev-database-reference-sql-functions-string-regexp-replace) for patterns. - **Case-sensitive.** `replace('Abc', 'a', 'x')` changes nothing. - **No match across normalisation forms.** A precomposed `é` doesn't match `e` followed by U+0301. Normalise with [nfc_normalize](/develop/docs/dev-database-reference-sql-functions-string-nfc-normalize) first if your data mixes them. - **NULL in any argument gives NULL,** including a NULL `source` or `target`. ``` run("SELECT replace(DATE '2026-10-16', '-', '/')") run("SELECT replace(CAST(123 AS VARCHAR), '2', '-')") ``` ``` InternalError: Binder Error: No function matches the given name and argument types 'replace(DATE, STRING_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts. [('1-3',)] ``` ## Similar functions | Function | What it replaces | Call | Result | | --- | --- | --- | --- | | `replace` | each occurrence of the substring `source` | `replace('abcabc', 'ab', 'x')` | `'xcxc'` | | [translate](/develop/docs/dev-database-reference-sql-functions-string-translate) | single characters: `a` becomes `x`, and `b`, which has no counterpart, is removed | `translate('abcabc', 'ab', 'x')` | `'xcxc'` | | [regexp_replace](/develop/docs/dev-database-reference-sql-functions-string-regexp-replace) | matches of a regular expression, here with the `'g'` option | `regexp_replace('abcabc', 'ab', 'x', 'g')` | `'xcxc'` | | `replace` | `'aa'`, without overlaps | `replace('aaa', 'aa', 'b')` | `'ba'` | | [translate](/develop/docs/dev-database-reference-sql-functions-string-translate) | each `a`; the second `a` in `from` is ignored | `translate('aaa', 'aa', 'xy')` | `'xxx'` | The first three calls return the same string for different reasons; the last two show the difference between a substring and a set of characters. [reverse](/develop/docs/dev-database-reference-sql-functions-string-reverse) and [repeat](/develop/docs/dev-database-reference-sql-functions-string-repeat) are the other functions that change text. ``` run("SELECT replace('abcabc', 'ab', 'x'), translate('abcabc', 'ab', 'x'), regexp_replace('abcabc', 'ab', 'x', 'g')") run("SELECT replace('aaa', 'aa', 'b'), translate('aaa', 'aa', 'xy')") ``` ``` [('xcxc', 'xcxc', 'xcxc')] [('ba', 'xxx')] ``` 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. - [Regular expressions](/develop/docs/dev-database-reference-sql-functions-string-regular-expressions): pattern matching and `regexp_replace`. - [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.