String Functions

DuckDB string scalar functions as typed Diesel DSL: case, trim, reverse, repeat, replace, search and position, padding, split/concat, similarity metrics, regex functions, printf-style formatting, hashing, and BLOB/base64/hex encoding.

DuckDB’s string scalar functions, exposed as typed free functions in better_duck_diesel::dsl::*. Call them in .select, .filter, or UPDATE … SET; the SQL type each returns is noted so you know the Rust type it loads as (see Type mapping).

use diesel::prelude::*;
use better_duck_diesel::dsl::*;

let shout: Vec<String> = products::table.select(upper(products::name)).load(&mut conn)?;

Only the functions listed here are implemented — do not assume an arbitrary DuckDB function is bound.

Case, trim, and basic transforms

Text -> Text unless noted:

lower, upper, trim, ltrim, rtrim, reverse, repeat(x, n: Integer), replace(s, from, to), length(s) (→BigInt), md5(x) (→Text), contains(haystack, needle) (→Bool), starts_with(s, prefix) (→Bool), ends_with(s, suffix) (→Bool).

let n: i64 = diesel::select(length("abcde")).get_result(&mut conn)?; // 5

Search, position, and extraction

strpos(haystack, needle) (→BigInt), instr(haystack, needle) (→BigInt), substr(s, start: Integer, length: Integer) (→Text), split_part(s, sep, index: Integer) (→Text), left(s, n: Integer) (→Text), right(s, n: Integer) (→Text), ascii(s) (→Integer), chr(code: Integer) (→Text).

Padding and joining

lpad(s, len: Integer, fill) (→Text), rpad(s, len: Integer, fill) (→Text), concat(a, b) (→Text), concat_ws(sep, a, b) (→Text).

Similarity and distance

Edit-distance and similarity metrics:

Function	Returns
levenshtein(a, b)	BigInt
damerau_levenshtein(a, b)	BigInt
hamming(a, b)	BigInt
mismatches(a, b)	BigInt
jaccard(a, b)	Double
jaro_similarity(a, b)	Double
jaro_winkler_similarity(a, b)	Double

Regex

Function forms (distinct from the ~/!~ operators):

regexp_matches(s, pattern) (→Bool), regexp_full_match(s, pattern) (→Bool), regexp_replace(s, pattern, replacement) (→Text), regexp_extract(s, pattern) (→Text).

let digits: Vec<String> = logs::table
    .select(regexp_extract(logs::line, r"\d+"))
    .load(&mut conn)?;

printf-style formatting

printf(format, arg) (→Text), format_(format, arg) (#[sql_name = "format"], →Text).

The function is named format_ in Rust because format is a reserved-ish identifier; it emits format(...) SQL via #[sql_name = "format"].

Hashing

md5(x) (→Text, also listed above), sha1(x) (→Text), sha256(x) (→Text).

Encoding — BLOB / base64 / hex

Function	Signature	Returns
encode(x)	Text	Binary
decode(b)	Binary	Text
base64(b)	Binary	Text
from_base64(s)	Text	Binary
hex(b)	Binary	Text
unhex(s)	Text	Binary

let hexed: String = diesel::select(hex(encode("hi"))).get_result(&mut conn)?;

See also

Operators

ILIKE / GLOB / regex operator forms.

Numeric & utility

Math and conditional functions.

Aggregates

string_agg, array_agg, and more.

Type mapping

What Text/Binary/BigInt load as.