String Functions in Confluent Cloud for Apache Flink

Confluent Cloud for Apache Flink® provides these built-in string functions to use in SQL queries:

ASCII BTRIM string1 || string2 CHARACTER_LENGTH
CHR CONCAT CONCAT_WS DECODE
ELT ENCODE FROM_BASE64 INITCAP
INSTR LEFT LOCATE LOWER
LPAD LTRIM OVERLAY PARSE_URL
POSITION REGEXP REGEXP_EXTRACT REGEXP_REPLACE
REPEAT REPLACE REVERSE RIGHT
RPAD RTRIM SPLIT_INDEX STR_TO_MAP
SUBSTRING TO_BASE64 TRANSLATE TRIM
UPPER URL_DECODE URL_ENCODE  

ASCII

Gets the ASCII value of the first character of a string.

Syntax
ASCII(string)
Description
The ASCII function returns the numeric value of the first character of the specified string. Returns NULL if string is NULL.
Examples
-- returns 97
SELECT ASCII('abc');

-- returns NULL
SELECT ASCII(CAST(NULL AS VARCHAR));

string1 || string2

Concatenates two strings.

Syntax
string1 || string2
Description
The || function returns the concatenation of string1 and string2.
Examples
-- returns "FlinkSQL"
SELECT 'Flink' || 'SQL';
Related functions

BTRIM

Trim both sides of a string.

Syntax
BTRIM(str[, trimStr])
Arguments
  • str: A source STRING expression.
  • trimStr: An optional STRING expression that has characters to be trimmed. The default is the space character.
Returns
A trimmed STRING.
Description
The BTRIM function trims the leading and trailing characters from str.
Examples
-- returns 'www.apache.org'
SELECT BTRIM("  www.apache.org  ");

-- returns 'www.apache.org'
SELECT BTRIM('/www.apache.org/', '/');

-- returns 'www.apache.org'
SELECT BTRIM('/*www.apache.org*/', '/*');
Related functions

CHARACTER_LENGTH

Gets the length of a string.

Syntax
CHARACTER_LENGTH(string)
Description

The CHARACTER_LENGTH function returns the number of characters in the specified string.

This function can be abbreviated to CHAR_LENGTH(string).

Examples
-- returns 18
SELECT CHAR_LENGTH('Thomas A. Anderson');

CHR

Gets the character for an ASCII code.

Syntax
CHR(integer)
Description

The CHR function returns the ASCII character that has the binary equivalent to the specified integer. Returns NULL if integer is NULL.

If integer is larger than 255, the function computes the modulus of integer divided by 255 first and returns CHR of the modulus.

Examples
-- returns 'a'
SELECT CHR(97);

-- returns 'a'
SELECT CHR(353);

CONCAT

Concatenates a list of strings.

Syntax
CONCAT(string1, string2, ...)
Description
The CONCAT function returns the concatenation of the specified strings. Returns NULL if any argument is NULL.
Example
--  returns "AABBCC"
SELECT CONCAT('AA', 'BB', 'CC');
Related functions

CONCAT_WS

Concatenates a list of strings with a separator.

Syntax
CONCAT_WS(string1, string2, string3, ...)
Description

The CONCAT_WS function returns a string that concatenates string2, string3, ... with the separator specified by string1.

The separator is added between the strings to be concatenated.

Returns NULL If string1 is NULL.

Example
-- returns "AA~BB~~CC"
SELECT CONCAT_WS('~', 'AA', 'BB', '', 'CC');
Related functions

DECODE

Decodes a binary into a string.

Syntax
DECODE(binary, string)
Description

The DECODE function decodes the binary argument into a string using the specified character set. Returns NULL if either argument is null.

These are the supported character set strings:

  • ‘ISO-8859-1’
  • ‘US-ASCII’
  • ‘UTF-8’
  • ‘UTF-16BE’
  • ‘UTF-16LE’
  • ‘UTF-16’
Related function

ELT

Gets the expression at the specified index.

Syntax
ELT(index, expr[, exprs]*)
Arguments
  • index: The 1-based index of the expression to get. index must be an integer between 1 and the number of expressions.
  • expr: An expression that resolves to CHAR, VARCHAR, BINARY, or VARBINARY.
Returns

The expression at the location in the argument list specified by index. The result has the type of the least common type of all expressions.

Returns NULL if index is NULL or out of range.

Description
Returns the index-th expression.
Example
-- returns java-2
SELECT ELT(2, 'scala-1', 'java-2', 'go-3');

ENCODE

Encodes a string to a BINARY.

Syntax
ENCODE(string1, string2)
Description

The ENCODE function encodes string1 into a BINARY using the specified string2 character set. Returns NULL if either argument is null.

These are the supported character set strings:

  • ‘ISO-8859-1’
  • ‘US-ASCII’
  • ‘UTF-8’
  • ‘UTF-16BE’
  • ‘UTF-16LE’
  • ‘UTF-16’
Related function

FROM_BASE64

Decodes a base-64 encoded string.

Syntax
FROM_BASE64(string)
Description
The FROM_BASE64 function returns the base64-decoded result from the specified string. Returns NULL if string is NULL.
Example
-- returns "hello world"
SELECT FROM_BASE64('aGVsbG8gd29ybGQ=');
Related function

INITCAP

Titlecase a string.

Syntax
INITCAP(string)
Description

The INITCAP function returns a string that has the first character of each word converted to uppercase and the other characters converted to lowercase.

A “word” is assumed to be a sequence of alphanumeric characters.

Example
-- returns "Title Case This String"
SELECT INITCAP('title case this string');
Related functions

INSTR

Find a substring in a string.

Syntax
INSTR(string1, string2)
Description

The INSTR function returns the position of the first occurrence of string2 in string1. Returns NULL if either argument is NULL.

The search is case-sensitive.

Example
-- returns 33
SELECT INSTR('The quick brown fox jumped over the lazy dog.', 'the');
Related function

LEFT

Gets the leftmost characters in a string.

Syntax
LEFT(string, integer)
Description
The LEFT function returns the leftmost integer characters from the specified string. Returns an empty string if integer is negative. Returns NULL if either argument is NULL.
Example
-- returns "Morph"
SELECT LEFT('Morpheus', 5);
Related function

LOCATE

Finds a substring in a string after a specified position.

Syntax
LOCATE(string1, string2[, integer])
Description
The LOCATE function returns the position of the first occurrence of string1 in string2 after position integer. Returns 0 if string1 isn’t found. Returns NULL if any of the arguments is NULL.
Example
-- returns 12
SELECT LOCATE('the', 'the play’s the thing', 10);

LOWER

Lowercases a string.

Syntax
LOWER(string)
Description

The LOWER function returns the specified string in lowercase.

To uppercase a string, use the UPPER function.

Example
-- returns "the quick brown fox jumped over the lazy dog."
SELECT LOWER('The Quick Brown Fox Jumped Over The Lazy Dog.');
Related functions

LPAD

Left-pad a string.

Syntax
LPAD(string1, integer, string2)
Description

The LPAD function returns a new string from string1 that’s left-padded with string2 to a length of integer characters.

If the length of string1 is shorter than integer, the LPAD function returns string1 shortened to integer characters.

To right-pad a string, use the RPAD function.

Examples
-- returns "??hi"
SELECT LPAD('hi', 4, '??');

-- returns "h"
SELECT LPAD('hi', 1, '??');

Related function - RPAD

LTRIM

Removes left whitespaces from a string.

Syntax
LTRIM(string)
Description

The LTRIM function removes the left whitespaces from the specified string.

To remove the right whitespaces from a string, use the RTRIM function.

Example
-- returns "This is a test string."
SELECT LTRIM(' This is a test string.');
Related functions

OVERLAY

Replaces characters in a string with another string.

Syntax
OVERLAY(string1 PLACING string2 FROM integer1 [ FOR integer2 ])
Description

The OVERLAY function returns a string that replaces integer2 characters of string1 with string2, starting from position integer1.

If integer2 isn’t specified, the default is the length of string2.

Examples
-- returns "xxxxxxxxx"
SELECT OVERLAY('xxxxxtest' PLACING 'xxxx' FROM 6);

-- returns "xxxxxxxxxst"
SELECT OVERLAY('xxxxxtest' PLACING 'xxxx' FROM 6 FOR 2);
Related functions

PARSE_URL

Gets parts of a URL.

Syntax
PARSE_URL(string1, string2[, string3])
Description

The PARSE_URL function returns the part specified by string2 from the URL in string1.

For a URL that has a query, the optional string3 argument specifies the key to extract from the query string.

Returns NULL if string1 or string2 is NULL.

These are the valid values for string2:

  • ‘AUTHORITY’
  • ‘FILE’
  • ‘HOST’
  • ‘PATH’
  • ‘PROTOCOL’
  • ‘QUERY’
  • ‘REF’
  • ‘USERINFO’
Example
-- returns 'confluent.io'
SELECT PARSE_URL('http://confluent.io/path1/p.php?k1=v1&k2=v2#Ref1', 'HOST');

-- returns 'v1'
SELECT PARSE_URL('http://confluent.io/path1/p.php?k1=v1&k2=v2#Ref1', 'QUERY', 'k1');

POSITION

Finds a substring in a string.

Syntax
POSITION(string1 IN string2)
Description

The POSITION function returns the position of the first occurrence of string1 in string2. Returns 0 if string1 isn’t found in string2.

The position is 1-based, so the index of the first character is 1.

Examples
-- returns 1
SELECT POSITION('the' IN 'the quick brown fox');

-- returns 17
SELECT POSITION('fox' IN 'the quick brown fox');

REGEXP

Matches a string against a regular expression.

Syntax
REGEXP(string1, string2)
Description
The REGEXP function returns TRUE if any (possibly empty) substring of string1 matches the regular expression in string2; otherwise, FALSE. Returns NULL if either of the arguments is NULL.
Examples
-- returns TRUE
SELECT REGEXP('800 439 3207', '.?(\d{3}).*(\d{3}).*(\d{4})');

-- returns TRUE
SELECT REGEXP('2023-05-04', '((\d{4}.\d{2}).(\d{2}))');

REGEXP_EXTRACT

Gets a string from a regular expression matching group.

Syntax
REGEXP_EXTRACT(string1, string2[, integer])
Description

The REGEXP_EXTRACT function returns a string from string1 that’s extracted with the regular expression specified in string2 and a regex match group index integer.

The regex match group index starts from 1, and 0 specifies matching the whole regex.

The regex match group index must not exceed the number of the defined groups.

Example
-- returns "bar"
SELECT REGEXP_EXTRACT('foothebar', 'foo(.*?)(bar)', 2);

REGEXP_REPLACE

Replaces substrings in a string that match a regular expression.

Syntax
REGEXP_REPLACE(string1, string2, string3)
Description
The REGEXP_REPLACE function returns a string from string1 with all of the substrings that match the regular expression in string2 consecutively replaced with string3.
Example
--  returns "fb"
SELECT REGEXP_REPLACE('foobar', 'oo|ar', '');
Related functions

REPEAT

Concatenates copies of a string.

Syntax
REPEAT(string, integer)
Description
The REPEAT function returns a string that repeats the base string integer times.
Example
-- returns "TestingTesting"
SELECT REPEAT('Testing', 2);

REPLACE

Replace substrings in a string.

Syntax
REPLACE(string1, string2, string3)
Description
The REPLACE function returns a new string that replaces all occurrences of string2 with string3 (non-overlapping) from string1.
Examples
-- returns "hello flink"
SELECT REPLACE('hello world', 'world', 'flink');

-- returns "zab"
SELECT REPLACE('ababab', 'abab', 'z');
Related functions

REVERSE

Reverses a string.

Syntax
REVERSE(string)
Description
The REVERSE function returns the reversed string. Returns NULL if string is NULL.
Example
-- returns "xof nworb kciuq eht"
SELECT REVERSE('the quick brown fox');

RPAD

Right-pad a string.

Syntax
RPAD(string1, integer, string2)
Description

The RPAD function returns a new string from string1 that’s right-padded with string2 to a length of integer characters.

If the length of string1 is shorter than integer, returns string1 shortened to integer characters.

To left-pad a string, use the LPAD function.

Examples
-- returns "hi??"
SELECT RPAD('hi', 4, '??');

-- returns "h"
SELECT RPAD('hi', 1, '??');
Related function

RTRIM

Removes right whitespaces from a string.

Syntax
RTRIM(string)
Description

The RTRIM function removes the right whitespaces from the specified string.

To remove the left whitespaces from a string, use the LTRIM function.

Example
-- returns "This is a test string."
SELECT RTRIM('This is a test string. ');
Related functions

SPLIT_INDEX

Splits a string by a delimiter.

Syntax
SPLIT_INDEX(string1, string2, integer1)
Description
The SPLIT_INDEX function splits string1 by the delimiter in string2 and returns the integer1 zero-based string of the split strings. Returns NULL if integer is negative. Returns NULL if any of the arguments is NULL.
Example
-- returns "fox"
SELECT SPLIT_INDEX('The quick brown fox', ' ', 3);

STR_TO_MAP

Creates a map from a list of key-value strings.

Syntax
STR_TO_MAP(string1[, string2, string3])
Description

The STR_TO_MAP function returns a map after splitting string1 into key/value pairs using the pair delimiter specified in string2. The default is ','. The string3 argument specifies the key-value delimiter. The default is '='.

Both the pair delimiter and the key-value delimiter are treated as regular expressions, so special characters, like <([{\^-=$!|]})?*+.>), must be properly escaped before using as a delimiter literal.

Example
-- returns {a=1, b=2, c=3}
SELECT STR_TO_MAP('a=1,b=2,c=3');

-- returns {a=1, b=2, c=3}
SELECT STR_TO_MAP('a:1;b:2;c:3', ';', ':');

SUBSTRING

Finds a substring in a string.

Syntax
SUBSTRING(string, integer1 [ FOR integer2 ])
Description

The SUBSTRING function returns a substring of the specified string, starting from position integer1 with length integer2.

If integer2 isn’t specified, the substring runs to the end of string.

This function can be abbreviated to SUBSTR(string, integer1[, integer2]).

Examples
-- returns "fox"
SELECT SUBSTR('The quick brown fox', 17);

-- returns "The"
SELECT SUBSTR('The quick brown fox', 1, 3);

TO_BASE64

Encodes a string to base64.

Syntax
TO_BASE64(string)
Description
The TO_BASE64 function returns the base64-encoded representation of the specified string. Returns NULL if string is NULL.
Example
-- returns "aGVsbG8gd29ybGQ="
SELECT TO_BASE64('hello world');
Related function

TRANSLATE

Substitutes characters in a string.

Syntax
TRANSLATE(expr, from, to)
Arguments
  • expr: A source STRING expression.
  • from: A STRING expression that specifies a set of characters to be replaced.
  • to: A STRING expression that specifies a corresponding set of replacement characters.
Returns
A STRING that has the characters of expr replaced with the characters specified in the to string.
Description

The TRANSLATE function replaces the characters in the expr source string according to the replacement rules specified in the from and to strings.

The replacement is case-sensitive.

-- returns A1B2C3
SELECT TRANSLATE('AaBbCc', 'abc', '123');

-- returns A1BC
SELECT TRANSLATE('AaBbCc', 'abc', '1');

-- returns ABC
SELECT TRANSLATE('AaBbCc', 'abc', '');
Related functions

TRIM

Removes leading and/or trailing characters from a string.

Syntax
TRIM([ BOTH | LEADING | TRAILING ] string1 FROM string2)
Description
The TRIM function returns a string that removes leading and/or trailing characters string2 from string1.
Examples
-- returns "The quick brown "
SELECT TRIM(TRAILING 'fox' FROM 'The quick brown fox');

-- returns " quick brown fox"
SELECT TRIM(LEADING 'The' FROM 'The quick brown fox');

-- returns " The quick brown fox "
SELECT TRIM(BOTH 'yyy' FROM 'yyy The quick brown fox yyy');
Related functions

UPPER

Uppercases a string.

Syntax
UPPER(string)
Description

The UPPER function returns the specified string in uppercase.

To lowercase a string, use the LOWER function.

Example
-- returns "THE QUICK BROWN FOX"
SELECT UPPER('The quick brown fox');

URL_DECODE

Decodes a URL string.

Syntax
URL_DECODE(string)
Description

The URL_DECODE function decodes the specified string in application/x-www-form-urlencoded format using the UTF-8 encoding scheme.

If the input string is NULL, or there is an issue with the decoding process, like encountering an illegal escape pattern, or the encoding scheme is not supported, the function returns NULL.

Example
-- returns "http://confluent.io"
SELECT URL_DECODE('http%3A%2F%2Fconfluent.io');

URL_ENCODE

Encodes a URL string.

Syntax
URL_ENCODE(string)
Description

The URL_ENCODE function translates the specified string into application/x-www-form-urlencoded format using the UTF-8 encoding scheme.

If the input string is NULL, or there is an issue with the decoding process, like encountering an illegal escape pattern, or the encoding scheme is not supported, the function returns NULL.

Example
-- returns "http%3A%2F%2Fconfluent.io"
SELECT URL_ENCODE('http://confluent.io');

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