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String functions and operators

String operators

The || operator performs concatenation.

The LIKE statement can be used for pattern matching and is documented in Pattern Comparison: LIKE

String functions

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 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 lower() and 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.

chr

chr(n) -> varchar

Returns the Unicode code point n as a single character string.

codepoint

codepoint(string) -> integer

Returns the Unicode code point of the only character of string.

concat

concat(string1, ..., stringN) -> varchar

Returns the concatenation of string1, string2, ..., stringN. This function provides the same functionality as the SQL-standard concatenation operator (||).

concat_ws

concat_ws(string0, string1, ..., stringN) -> varchar

Returns the concatenation of string1, string2, ..., stringN using string0 as a separator. If string0 is null, then the return value is null. Any null values provided in the arguments after the separator are skipped.

concat_ws(string0, array(varchar)) -> varchar

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.

format

format(format, args...) -> varchar

See format().

hamming_distance

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.

length

length(string) -> bigint

Returns the length of string in characters.

levenshtein_distance

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.

lower

lower(string) -> varchar

Converts string to lowercase.

lpad

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.

ltrim

ltrim(string) -> varchar

Removes leading whitespace from string.

luhn_check

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

position

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.

This SQL-standard function has special syntax and uses the IN keyword for the arguments. See also strpos().

replace

replace(string, search) -> varchar

Removes all instances of search from string.

replace(string, search, replace) -> varchar

Replaces all instances of search with replace in string.

reverse

reverse(string) -> varchar

Returns string with the characters in reverse order.

rpad

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.

rtrim

rtrim(string) -> varchar

Removes trailing whitespace from string.

soundex

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)

split

split(string, delimiter) -> array(varchar)

Splits string on delimiter and returns an array.

split(string, delimiter, limit) -> array(varchar)

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.

split_part

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.

split_to_map

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.

split_to_multimap

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.

strpos

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.

strpos(string, substring, instance) -> bigint

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.

starts_with

starts_with(string, substring) -> boolean

Tests whether substring is a prefix of string.

substr

substr(string, start) -> varchar

This is an alias for substring().

substr(string, start, length) -> varchar

This is an alias for substring().

substring

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.

substring(string, start, length) -> varchar

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.

translate

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'

trime

trim(string) -> varchar

Removes leading and trailing whitespace from string.

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'

upper

upper(string) -> varchar

Converts string to uppercase.

word_stem

word_stem(word) -> varchar

Returns the stem of word in the English language.

word_stem(word, lang) -> varchar

Returns the stem of word in the lang language.

Unicode functions

normalize

normalize(string) -> varchar
Transforms `string` with NFC normalization form.

normalize(string, form) -> varchar

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

Form	Description
`NFD`	Canonical Decomposition
`NFC`	Canonical Decomposition, followed by Canonical Composition
`NFKD`	Compatibility Decomposition
`NFKC`	Compatibility Decomposition, followed by Canonical Composition

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

to_utf8

to_utf8(string) -> varbinary

Encodes string into a UTF-8 varbinary representation.

from_utf8

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.

from_utf8(binary, replace) -> varchar

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).