Presto 337 Documentation

8.9. String Functions and Operators

8.9. 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#

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 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(n) → varchar#

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

codepoint(string) → integer#

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

concat(string1, ..., stringN) → varchar#

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

format(format, args...) → varchar

See format().

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(string) → bigint#

Returns the length of string in characters.

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(string) → varchar#

Converts string to lowercase.

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(string) → varchar#

Removes leading whitespace from string.

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 strpos().

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(string) → varchar#

Returns string with the characters in reverse order.

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(string) → varchar#

Removes trailing whitespace from string.

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(string, delimiter, index) → varchar#

Splits string on delimiter and returns the field index. Field indexes start with 1. If the index is larger than than the number of fields, then null is returned.

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(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(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(string, substring) → boolean#

Tests whether substring is a prefix of string.

substr(string, start) → varchar#

This is an alias for 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.

substr(string, start, length) → varchar

This is an alias for substring().

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(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'
trim(string) → varchar#

Removes leading and trailing whitespace from string.

upper(string) → varchar#

Converts string to uppercase.

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(string) → varchar#

Transforms string with NFC normalization form.

normalize(string, form) → varchar

Transforms string with the specified normalization form. form must be 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

Note

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

to_utf8(string) → varbinary#

Encodes string into a UTF-8 varbinary representation.

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).