String functions and operators

String operators

The || operator performs concatenation.

The LIKE statement can be used for pattern matching and is documented in {ref}like-operator.

String functions

:::{note} These functions assume that the input strings contain valid UTF-8 encoded Unicode code points. There are no explicit checks for valid UTF-8 and the functions may return incorrect results on invalid UTF-8. Invalid UTF-8 data can be corrected with {func}from_utf8.

Additionally, the functions operate on Unicode code points and not user visible characters (or grapheme clusters). Some languages combine multiple code points into a single user-perceived character, the basic unit of a writing system for a language, but the functions will treat each code point as a separate unit.

The {func}lower and {func}upper functions do not perform locale-sensitive, context-sensitive, or one-to-many mappings required for some languages. Specifically, this will return incorrect results for Lithuanian, Turkish and Azeri. :::

:::{function} chr(n) -> varchar Returns the Unicode code point n as a single character string. :::

:::{function} codepoint(string) -> integer Returns the Unicode code point of the only character of string. :::

:::{function} concat(string1, ..., stringN) -> varchar Returns the concatenation of string1, string2, ..., stringN. This function provides the same functionality as the SQL-standard concatenation operator (||). :::

:::{function} concat_ws(separator, string1, ..., stringN) -> varchar Returns the concatenation of string1, string2, ..., stringN using separator to join the values. If separator is null, then the return value is null. Any null values provided in the arguments after the separator are skipped. :::

:::{function} concat_ws(string0, array(varchar)) -> varchar :noindex: true

Returns the concatenation of elements in the array using string0 as a separator. If string0 is null, then the return value is null. Any null values in the array are skipped. :::

:::{function} format(format, args...) -> varchar :noindex: true

See {func}format. :::

:::{function} hamming_distance(string1, string2) -> bigint Returns the Hamming distance of string1 and string2, i.e. the number of positions at which the corresponding characters are different. Note that the two strings must have the same length. :::

:::{function} length(string) -> bigint Returns the length of string in characters. :::

:::{function} levenshtein_distance(string1, string2) -> bigint Returns the Levenshtein edit distance of string1 and string2, i.e. the minimum number of single-character edits (insertions, deletions or substitutions) needed to change string1 into string2. :::

:::{function} lower(string) -> varchar Converts string to lowercase. :::

:::{function} lpad(string, size, padstring) -> varchar Left pads string to size characters with padstring. If size is less than the length of string, the result is truncated to size characters. size must not be negative and padstring must be non-empty. :::

:::{function} ltrim(string) -> varchar Removes leading whitespace from string. :::

:::{function} luhn_check(string) -> boolean Tests whether a string of digits is valid according to the Luhn algorithm.

This checksum function, also known as modulo 10 or mod 10, is widely applied on credit card numbers and government identification numbers to distinguish valid numbers from mistyped, incorrect numbers.

Valid identification number:

select luhn_check('79927398713');
-- true

Invalid identification number:

select luhn_check('79927398714');
-- false

:::

::::{function} position(substring IN string) -> bigint Returns the starting position of the first instance of substring in string. Positions start with 1. If not found, 0 is returned.

:::{note} This SQL-standard function has special syntax and uses the IN keyword for the arguments. See also {func}strpos. ::: ::::

:::{function} replace(string, search) -> varchar Removes all instances of search from string. :::

:::{function} replace(string, search, replace) -> varchar :noindex: true

Replaces all instances of search with replace in string. :::

:::{function} reverse(string) -> varchar Returns string with the characters in reverse order. :::

:::{function} rpad(string, size, padstring) -> varchar Right pads string to size characters with padstring. If size is less than the length of string, the result is truncated to size characters. size must not be negative and padstring must be non-empty. :::

:::{function} rtrim(string) -> varchar Removes trailing whitespace from string. :::

:::{function} soundex(char) -> string soundex returns a character string containing the phonetic representation of char.

: It is typically used to evaluate the similarity of two expressions phonetically, that is how the string sounds when spoken:

SELECT name
FROM nation
WHERE SOUNDEX(name)  = SOUNDEX('CHYNA');

 name  |
-------+----
 CHINA |
(1 row)

:::

:::{function} split(string, delimiter) -> array(varchar) Splits string on delimiter and returns an array. :::

:::{function} split(string, delimiter, limit) -> array(varchar) :noindex: true

Splits string on delimiter and returns an array of size at most limit. The last element in the array always contain everything left in the string. limit must be a positive number. :::

:::{function} split_part(string, delimiter, index) -> varchar Splits string on delimiter and returns the field index. Field indexes start with 1. If the index is larger than the number of fields, then null is returned. :::

:::{function} split_to_map(string, entryDelimiter, keyValueDelimiter) -> map<varchar, varchar> Splits string by entryDelimiter and keyValueDelimiter and returns a map. entryDelimiter splits string into key-value pairs. keyValueDelimiter splits each pair into key and value. :::

:::{function} split_to_multimap(string, entryDelimiter, keyValueDelimiter) -> map(varchar, array(varchar)) Splits string by entryDelimiter and keyValueDelimiter and returns a map containing an array of values for each unique key. entryDelimiter splits string into key-value pairs. keyValueDelimiter splits each pair into key and value. The values for each key will be in the same order as they appeared in string. :::

:::{function} strpos(string, substring) -> bigint Returns the starting position of the first instance of substring in string. Positions start with 1. If not found, 0 is returned. :::

:::{function} strpos(string, substring, instance) -> bigint :noindex: true

Returns the position of the N-th instance of substring in string. When instance is a negative number the search will start from the end of string. Positions start with 1. If not found, 0 is returned. :::

:::{function} starts_with(string, substring) -> boolean Tests whether substring is a prefix of string. :::

:::{function} substr(string, start) -> varchar This is an alias for {func}substring. :::

:::{function} substring(string, start) -> varchar Returns the rest of string from the starting position start. Positions start with 1. A negative starting position is interpreted as being relative to the end of the string. :::

:::{function} substr(string, start, length) -> varchar :noindex: true

This is an alias for {func}substring. :::

:::{function} substring(string, start, length) -> varchar :noindex: true

Returns a substring from string of length length from the starting position start. Positions start with 1. A negative starting position is interpreted as being relative to the end of the string. :::

:::{function} translate(source, from, to) -> varchar Returns the source string translated by replacing characters found in the from string with the corresponding characters in the to string. If the from string contains duplicates, only the first is used. If the source character does not exist in the from string, the source character will be copied without translation. If the index of the matching character in the from string is beyond the length of the to string, the source character will be omitted from the resulting string.

Here are some examples illustrating the translate function:

SELECT translate('abcd', '', ''); -- 'abcd'
SELECT translate('abcd', 'a', 'z'); -- 'zbcd'
SELECT translate('abcda', 'a', 'z'); -- 'zbcdz'
SELECT translate('Palhoça', 'ç','c'); -- 'Palhoca'
SELECT translate('abcd', 'b', U&'\+01F600'); -- a😀cd
SELECT translate('abcd', 'a', ''); -- 'bcd'
SELECT translate('abcd', 'a', 'zy'); -- 'zbcd'
SELECT translate('abcd', 'ac', 'z'); -- 'zbd'
SELECT translate('abcd', 'aac', 'zq'); -- 'zbd'

:::

:::{function} trim(string) -> varchar :noindex: true

Removes leading and trailing whitespace from string. :::

:::{function} trim( [ [ specification ] [ string ] FROM ] source ) -> varchar Removes any leading and/or trailing characters as specified up to and including string from source:

SELECT trim('!' FROM '!foo!'); -- 'foo'
SELECT trim(LEADING FROM '  abcd');  -- 'abcd'
SELECT trim(BOTH '$' FROM '$var$'); -- 'var'
SELECT trim(TRAILING 'ER' FROM upper('worker')); -- 'WORK'

:::

:::{function} upper(string) -> varchar Converts string to uppercase. :::

:::{function} word_stem(word) -> varchar Returns the stem of word in the English language. :::

:::{function} word_stem(word, lang) -> varchar :noindex: true

Returns the stem of word in the lang language. :::

Unicode functions

:::{function} normalize(string) -> varchar Transforms string with NFC normalization form. :::

::::{function} normalize(string, form) -> varchar :noindex: true

Transforms string with the specified normalization form. form must be one of the following keywords:

:::{note} This SQL-standard function has special syntax and requires specifying form as a keyword, not as a string. ::: ::::

:::{function} to_utf8(string) -> varbinary Encodes string into a UTF-8 varbinary representation. :::

:::{function} from_utf8(binary) -> varchar Decodes a UTF-8 encoded string from binary. Invalid UTF-8 sequences are replaced with the Unicode replacement character U+FFFD. :::

:::{function} from_utf8(binary, replace) -> varchar :noindex: true

Decodes a UTF-8 encoded string from binary. Invalid UTF-8 sequences are replaced with replace. The replacement string replace must either be a single character or empty (in which case invalid characters are removed). :::