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Functions for Working with Strings

Functions for searching in strings and for replacing in strings are described separately.

empty​

Checks whether the input string is empty. A string is considered non-empty if it contains at least one byte, even if this byte is a space or the null byte.

The function is also available for arrays and UUIDs.

Syntax

empty(x)

Arguments

Returned value

  • Returns 1 for an empty string or 0 for a non-empty string. UInt8.

Example

SELECT empty('');

Result:

┌─empty('')─┐
│         1 │
└───────────┘

notEmpty​

Checks whether the input string is non-empty. A string is considered non-empty if it contains at least one byte, even if this byte is a space or the null byte.

The function is also available for arrays and UUIDs.

Syntax

notEmpty(x)

Arguments

Returned value

  • Returns 1 for a non-empty string or 0 for an empty string string. UInt8.

Example

SELECT notEmpty('text');

Result:

┌─notEmpty('text')─┐
│                1 │
└──────────────────┘

length​

Returns the length of a string in bytes rather than in characters or Unicode code points. The function also works for arrays.

Alias: OCTET_LENGTH

Syntax

length(s)

Parameters

Returned value

  • Length of the string or array s in bytes. UInt64.

Example

Query:

SELECT length('Hello, world!');

Result: 

┌─length('Hello, world!')─┐
│                      13 │
└─────────────────────────┘

Query:

SELECT length([1, 2, 3, 4]);

Result: 

┌─length([1, 2, 3, 4])─┐
│                    4 │
└──────────────────────┘

lengthUTF8​

Returns the length of a string in Unicode code points rather than in bytes or characters. It assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Aliases:

  • CHAR_LENGTH
  • CHARACTER_LENGTH

Syntax

lengthUTF8(s)

Parameters

  • s — String containing valid UTF-8 encoded text. String.

Returned value

  • Length of the string s in Unicode code points. UInt64.

Example

Query:

SELECT lengthUTF8('Здравствуй, мир!');

Result: 

┌─lengthUTF8('Здравствуй, мир!')─┐
│                             16 │
└────────────────────────────────┘

left​

Returns a substring of string s with a specified offset starting from the left.

Syntax

left(s, offset)

Parameters

  • s — The string to calculate a substring from. String or FixedString.
  • offset — The number of bytes of the offset. UInt*.

Returned value

  • For positive offset: A substring of s with offset many bytes, starting from the left of the string.
  • For negative offset: A substring of s with length(s) - |offset| bytes, starting from the left of the string.
  • An empty string if length is 0.

Example

Query:

SELECT left('Hello', 3);

Result:

Hel

Query:

SELECT left('Hello', -3);

Result:

He

leftUTF8​

Returns a substring of a UTF-8 encoded string s with a specified offset starting from the left.

Syntax

leftUTF8(s, offset)

Parameters

  • s — The UTF-8 encoded string to calculate a substring from. String or FixedString.
  • offset — The number of bytes of the offset. UInt*.

Returned value

  • For positive offset: A substring of s with offset many bytes, starting from the left of the string.
  • For negative offset: A substring of s with length(s) - |offset| bytes, starting from the left of the string.
  • An empty string if length is 0.

Example

Query:

SELECT leftUTF8('Привет', 4);

Result:

Прив

Query:

SELECT leftUTF8('Привет', -4);

Result:

Пр

leftPad​

Pads a string from the left with spaces or with a specified string (multiple times, if needed) until the resulting string reaches the specified length.

Syntax

leftPad(string, length[, pad_string])

Alias: LPAD

Arguments

  • string — Input string that should be padded. String.
  • length — The length of the resulting string. UInt or Int. If the value is smaller than the input string length, then the input string is shortened to length characters.
  • pad_string — The string to pad the input string with. String. Optional. If not specified, then the input string is padded with spaces.

Returned value

  • A left-padded string of the given length. String.

Example

SELECT leftPad('abc', 7, '*'), leftPad('def', 7);

Result:

┌─leftPad('abc', 7, '*')─┬─leftPad('def', 7)─┐
│ ****abc                │     def           │
└────────────────────────┴───────────────────┘

leftPadUTF8​

Pads the string from the left with spaces or a specified string (multiple times, if needed) until the resulting string reaches the given length. Unlike leftPad which measures the string length in bytes, the string length is measured in code points.

Syntax

leftPadUTF8(string, length[, pad_string])

Arguments

  • string — Input string that should be padded. String.
  • length — The length of the resulting string. UInt or Int. If the value is smaller than the input string length, then the input string is shortened to length characters.
  • pad_string — The string to pad the input string with. String. Optional. If not specified, then the input string is padded with spaces.

Returned value

  • A left-padded string of the given length. String.

Example

SELECT leftPadUTF8('абвг', 7, '*'), leftPadUTF8('дежз', 7);

Result:

┌─leftPadUTF8('абвг', 7, '*')─┬─leftPadUTF8('дежз', 7)─┐
│ ***абвг                     │    дежз                │
└─────────────────────────────┴────────────────────────┘

Returns a substring of string s with a specified offset starting from the right.

Syntax

right(s, offset)

Parameters

  • s — The string to calculate a substring from. String or FixedString.
  • offset — The number of bytes of the offset. UInt*.

Returned value

  • For positive offset: A substring of s with offset many bytes, starting from the right of the string.
  • For negative offset: A substring of s with length(s) - |offset| bytes, starting from the right of the string.
  • An empty string if length is 0.

Example

Query:

SELECT right('Hello', 3);

Result:

llo

Query:

SELECT right('Hello', -3);

Result:

lo

rightUTF8​

Returns a substring of UTF-8 encoded string s with a specified offset starting from the right.

Syntax

rightUTF8(s, offset)

Parameters

  • s — The UTF-8 encoded string to calculate a substring from. String or FixedString.
  • offset — The number of bytes of the offset. UInt*.

Returned value

  • For positive offset: A substring of s with offset many bytes, starting from the right of the string.
  • For negative offset: A substring of s with length(s) - |offset| bytes, starting from the right of the string.
  • An empty string if length is 0.

Example

Query:

SELECT rightUTF8('Привет', 4);

Result:

ивет

Query:

SELECT rightUTF8('Привет', -4);

Result:

ет

rightPad​

Pads a string from the right with spaces or with a specified string (multiple times, if needed) until the resulting string reaches the specified length.

Syntax

rightPad(string, length[, pad_string])

Alias: RPAD

Arguments

  • string — Input string that should be padded. String.
  • length — The length of the resulting string. UInt or Int. If the value is smaller than the input string length, then the input string is shortened to length characters.
  • pad_string — The string to pad the input string with. String. Optional. If not specified, then the input string is padded with spaces.

Returned value

  • A left-padded string of the given length. String.

Example

SELECT rightPad('abc', 7, '*'), rightPad('abc', 7);

Result:

┌─rightPad('abc', 7, '*')─┬─rightPad('abc', 7)─┐
│ abc****                 │ abc                │
└─────────────────────────┴────────────────────┘

rightPadUTF8​

Pads the string from the right with spaces or a specified string (multiple times, if needed) until the resulting string reaches the given length. Unlike rightPad which measures the string length in bytes, the string length is measured in code points.

Syntax

rightPadUTF8(string, length[, pad_string])

Arguments

  • string — Input string that should be padded. String.
  • length — The length of the resulting string. UInt or Int. If the value is smaller than the input string length, then the input string is shortened to length characters.
  • pad_string — The string to pad the input string with. String. Optional. If not specified, then the input string is padded with spaces.

Returned value

  • A right-padded string of the given length. String.

Example

SELECT rightPadUTF8('абвг', 7, '*'), rightPadUTF8('абвг', 7);

Result:

┌─rightPadUTF8('абвг', 7, '*')─┬─rightPadUTF8('абвг', 7)─┐
│ абвг***                      │ абвг                    │
└──────────────────────────────┴─────────────────────────┘

lower​

Converts the ASCII Latin symbols in a string to lowercase.

*Syntax**

lower(input)

Alias: lcase

Parameters

Returned value

Example

Query:

SELECT lower('CLICKHOUSE');
┌─lower('CLICKHOUSE')─┐
│ clickhouse          │
└─────────────────────┘

upper​

Converts the ASCII Latin symbols in a string to uppercase.

Syntax

upper(input)

Alias: ucase

Parameters

  • input — A string type String.

Returned value

Examples

Query:

SELECT upper('clickhouse');
┌─upper('clickhouse')─┐
│ CLICKHOUSE          │
└─────────────────────┘

lowerUTF8​

Converts a string to lowercase, assuming that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Note

Does not detect the language, e.g. for Turkish the result might not be exactly correct (i/İ vs. i/I). If the length of the UTF-8 byte sequence is different for upper and lower case of a code point (such as ẞ and ß), the result may be incorrect for this code point.

Syntax

lowerUTF8(input)

Parameters

  • input — A string type String.

Returned value

Example

Query:

SELECT lowerUTF8('MÜNCHEN') as Lowerutf8;

Result:

┌─Lowerutf8─┐
│ münchen   │
└───────────┘

upperUTF8​

Converts a string to uppercase, assuming that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Note

Does not detect the language, e.g. for Turkish the result might not be exactly correct (i/İ vs. i/I). If the length of the UTF-8 byte sequence is different for upper and lower case of a code point (such as ẞ and ß), the result may be incorrect for this code point.

Syntax

upperUTF8(input)

Parameters

  • input — A string type String.

Returned value

Example

Query:

SELECT upperUTF8('München') as Upperutf8;

Result:

┌─Upperutf8─┐
│ MÜNCHEN   │
└───────────┘

isValidUTF8​

Returns 1, if the set of bytes constitutes valid UTF-8-encoded text, otherwise 0.

Syntax

isValidUTF8(input)

Parameters

  • input — A string type String.

Returned value

  • Returns 1, if the set of bytes constitutes valid UTF-8-encoded text, otherwise 0.

Query:

SELECT isValidUTF8('\xc3\xb1') AS valid, isValidUTF8('\xc3\x28') AS invalid;

Result:

┌─valid─┬─invalid─┐
│     1 │       0 │
└───────┴─────────┘

toValidUTF8​

Replaces invalid UTF-8 characters by the � (U+FFFD) character. All running in a row invalid characters are collapsed into the one replacement character.

Syntax

toValidUTF8(input_string)

Arguments

  • input_string — Any set of bytes represented as the String data type object.

Returned value

  • A valid UTF-8 string.

Example

SELECT toValidUTF8('\x61\xF0\x80\x80\x80b');
┌─toValidUTF8('a����b')─┐
│ a�b                   │
└───────────────────────┘

repeat​

Concatenates a string as many times with itself as specified.

Syntax

repeat(s, n)

Alias: REPEAT

Arguments

  • s — The string to repeat. String.
  • n — The number of times to repeat the string. UInt or Int.

Returned value

A string containing string s repeated n times. If n <= 0, the function returns the empty string. String.

Example

SELECT repeat('abc', 10);

Result:

┌─repeat('abc', 10)──────────────┐
│ abcabcabcabcabcabcabcabcabcabc │
└────────────────────────────────┘

space​

Concatenates a space ( ) as many times with itself as specified.

Syntax

space(n)

Alias: SPACE.

Arguments

  • n — The number of times to repeat the space. UInt or Int.

Returned value

The string containing string repeated n times. If n <= 0, the function returns the empty string. String.

Example

Query:

SELECT space(3);

Result:

┌─space(3) ────┐
│              │
└──────────────┘

reverse​

Reverses the sequence of bytes in a string.

reverseUTF8​

Reverses a sequence of Unicode code points in a string. Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

concat​

Concatenates the given arguments.

Syntax

concat(s1, s2, ...)

Arguments

Values of arbitrary type.

Arguments which are not of types String or FixedString are converted to strings using their default serialization. As this decreases performance, it is not recommended to use non-String/FixedString arguments.

Returned values

The String created by concatenating the arguments.

If any of arguments is NULL, the function returns NULL.

Example

Query:

SELECT concat('Hello, ', 'World!');

Result:

┌─concat('Hello, ', 'World!')─┐
│ Hello, World!               │
└─────────────────────────────┘

Query:

SELECT concat(42, 144);

Result:

┌─concat(42, 144)─┐
│ 42144           │
└─────────────────┘

concatAssumeInjective​

Like concat but assumes that concat(s1, s2, ...) → sn is injective. Can be used for optimization of GROUP BY.

A function is called injective if it returns for different arguments different results. In other words: different arguments never produce identical result.

Syntax

concatAssumeInjective(s1, s2, ...)

Arguments

Values of type String or FixedString.

Returned values

The String created by concatenating the arguments.

If any of argument values is NULL, the function returns NULL.

Example

Input table:

CREATE TABLE key_val(`key1` String, `key2` String, `value` UInt32) ENGINE = TinyLog;
INSERT INTO key_val VALUES ('Hello, ','World',1), ('Hello, ','World',2), ('Hello, ','World!',3), ('Hello',', World!',2);
SELECT * from key_val;
┌─key1────┬─key2─────┬─value─┐
│ Hello,  │ World    │     1 │
│ Hello,  │ World    │     2 │
│ Hello,  │ World!   │     3 │
│ Hello   │ , World! │     2 │
└─────────┴──────────┴───────┘
SELECT concat(key1, key2), sum(value) FROM key_val GROUP BY concatAssumeInjective(key1, key2);

Result:

┌─concat(key1, key2)─┬─sum(value)─┐
│ Hello, World!      │          3 │
│ Hello, World!      │          2 │
│ Hello, World       │          3 │
└────────────────────┴────────────┘

concatWithSeparator​

Concatenates the given strings with a given separator.

Syntax

concatWithSeparator(sep, expr1, expr2, expr3...)

Alias: concat_ws

Arguments

  • sep — separator. Const String or FixedString.
  • exprN — expression to be concatenated. Arguments which are not of types String or FixedString are converted to strings using their default serialization. As this decreases performance, it is not recommended to use non-String/FixedString arguments.

Returned values

The String created by concatenating the arguments.

If any of the argument values is NULL, the function returns NULL.

Example

SELECT concatWithSeparator('a', '1', '2', '3', '4')

Result:

┌─concatWithSeparator('a', '1', '2', '3', '4')─┐
│ 1a2a3a4                                      │
└──────────────────────────────────────────────┘

concatWithSeparatorAssumeInjective​

Like concatWithSeparator but assumes that concatWithSeparator(sep, expr1, expr2, expr3...) → result is injective. Can be used for optimization of GROUP BY.

A function is called injective if it returns for different arguments different results. In other words: different arguments never produce identical result.

substring​

Returns the substring of a string s which starts at the specified byte index offset. Byte counting starts from 1. If offset is 0, an empty string is returned. If offset is negative, the substring starts pos characters from the end of the string, rather than from the beginning. An optional argument length specifies the maximum number of bytes the returned substring may have.

Syntax

substring(s, offset[, length])

Aliases:

  • substr
  • mid
  • byteSlice

Arguments

  • s — The string to calculate a substring from. String, FixedString or Enum
  • offset — The starting position of the substring in s . (U)Int*.
  • length — The maximum length of the substring. (U)Int*. Optional.

Returned value

A substring of s with length many bytes, starting at index offset. String.

Example

SELECT 'database' AS db, substr(db, 5), substr(db, 5, 1)

Result:

┌─db───────┬─substring('database', 5)─┬─substring('database', 5, 1)─┐
│ database │ base                     │ b                           │
└──────────┴──────────────────────────┴─────────────────────────────┘

substringUTF8​

Returns the substring of a string s which starts at the specified byte index offset for Unicode code points. Byte counting starts from 1. If offset is 0, an empty string is returned. If offset is negative, the substring starts pos characters from the end of the string, rather than from the beginning. An optional argument length specifies the maximum number of bytes the returned substring may have.

Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Syntax

substringUTF8(s, offset[, length])

Arguments

  • s — The string to calculate a substring from. String, FixedString or Enum
  • offset — The starting position of the substring in s . (U)Int*.
  • length — The maximum length of the substring. (U)Int*. Optional.

Returned value

A substring of s with length many bytes, starting at index offset.

Implementation details

Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Example

SELECT 'Täglich grüßt das Murmeltier.' AS str,
       substringUTF8(str, 9),
       substringUTF8(str, 9, 5)
Täglich grüßt das Murmeltier.   grüßt das Murmeltier.   grüßt

substringIndex​

Returns the substring of s before count occurrences of the delimiter delim, as in Spark or MySQL.

Syntax

substringIndex(s, delim, count)

Alias: SUBSTRING_INDEX

Arguments

  • s — The string to extract substring from. String.
  • delim — The character to split. String.
  • count — The number of occurrences of the delimiter to count before extracting the substring. If count is positive, everything to the left of the final delimiter (counting from the left) is returned. If count is negative, everything to the right of the final delimiter (counting from the right) is returned. UInt or Int

Example

SELECT substringIndex('www.clickhouse.com', '.', 2)

Result:

┌─substringIndex('www.clickhouse.com', '.', 2)─┐
│ www.clickhouse                               │
└──────────────────────────────────────────────┘

substringIndexUTF8​

Returns the substring of s before count occurrences of the delimiter delim, specifically for Unicode code points.

Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Syntax

substringIndexUTF8(s, delim, count)

Arguments

  • s — The string to extract substring from. String.
  • delim — The character to split. String.
  • count — The number of occurrences of the delimiter to count before extracting the substring. If count is positive, everything to the left of the final delimiter (counting from the left) is returned. If count is negative, everything to the right of the final delimiter (counting from the right) is returned. UInt or Int

Returned value

A substring String of s before count occurrences of delim.

Implementation details

Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Example

SELECT substringIndexUTF8('www.straßen-in-europa.de', '.', 2)
www.straßen-in-europa

appendTrailingCharIfAbsent​

Appends character c to string s if s is non-empty and does not end with character c.

Syntax

appendTrailingCharIfAbsent(s, c)

convertCharset​

Returns string s converted from the encoding from to encoding to.

Syntax

convertCharset(s, from, to)

base58Encode​

Encodes a string using Base58 in the "Bitcoin" alphabet.

Syntax

base58Encode(plaintext)

Arguments

  • plaintext — String column or constant.

Returned value

Example

SELECT base58Encode('Encoded');

Result:

┌─base58Encode('Encoded')─┐
│ 3dc8KtHrwM              │
└─────────────────────────┘

base58Decode​

Accepts a string and decodes it using Base58 encoding scheme using "Bitcoin" alphabet.

Syntax

base58Decode(encoded)

Arguments

  • encoded — String or FixedString. If the string is not a valid Base58-encoded value, an exception is thrown.

Returned value

  • A string containing the decoded value of the argument. String.

Example

SELECT base58Decode('3dc8KtHrwM');

Result:

┌─base58Decode('3dc8KtHrwM')─┐
│ Encoded                    │
└────────────────────────────┘

tryBase58Decode​

Like base58Decode but returns an empty string in case of error.

Syntax

tryBase58Decode(encoded)

Parameters

  • encoded: String or FixedString. If the string is not a valid Base58-encoded value, returns an empty string in case of error.

Returned value

  • A string containing the decoded value of the argument.

Examples

Query:

SELECT tryBase58Decode('3dc8KtHrwM') as res, tryBase58Decode('invalid') as res_invalid;
┌─res─────┬─res_invalid─┐
│ Encoded │             │
└─────────┴─────────────┘

base64Encode​

Encodes a String or FixedString as base64, according to RFC 4648.

Alias: TO_BASE64.

Syntax

base64Encode(plaintext)

Arguments

  • plaintext — String column or constant.

Returned value

  • A string containing the encoded value of the argument.

Example

SELECT base64Encode('clickhouse');

Result:

┌─base64Encode('clickhouse')─┐
│ Y2xpY2tob3VzZQ==           │
└────────────────────────────┘

base64URLEncode​

Encodes an URL (String or FixedString) as base64 with URL-specific modifications, according to RFC 4648.

Syntax

base64URLEncode(url)

Arguments

  • url — String column or constant.

Returned value

  • A string containing the encoded value of the argument.

Example

SELECT base64URLEncode('https://clickhouse.com');

Result:

┌─base64URLEncode('https://clickhouse.com')─┐
│ aHR0cDovL2NsaWNraG91c2UuY29t              │
└───────────────────────────────────────────┘

base64Decode​

Accepts a String and decodes it from base64, according to RFC 4648. Throws an exception in case of an error.

Alias: FROM_BASE64.

Syntax

base64Decode(encoded)

Arguments

  • encoded — String column or constant. If the string is not a valid Base64-encoded value, an exception is thrown.

Returned value

  • A string containing the decoded value of the argument.

Example

SELECT base64Decode('Y2xpY2tob3VzZQ==');

Result:

┌─base64Decode('Y2xpY2tob3VzZQ==')─┐
│ clickhouse                       │
└──────────────────────────────────┘

base64URLDecode​

Accepts a base64-encoded URL and decodes it from base64 with URL-specific modifications, according to RFC 4648. Throws an exception in case of an error.

Syntax

base64URLDecode(encodedUrl)

Arguments

  • encodedURL — String column or constant. If the string is not a valid Base64-encoded value with URL-specific modifications, an exception is thrown.

Returned value

  • A string containing the decoded value of the argument.

Example

SELECT base64URLDecode('aHR0cDovL2NsaWNraG91c2UuY29t');

Result:

┌─base64URLDecode('aHR0cDovL2NsaWNraG91c2UuY29t')─┐
│ https://clickhouse.com                          │
└─────────────────────────────────────────────────┘

tryBase64Decode​

Like base64Decode but returns an empty string in case of error.

Syntax

tryBase64Decode(encoded)

Arguments

  • encoded — String column or constant. If the string is not a valid Base64-encoded value, returns an empty string.

Returned value

  • A string containing the decoded value of the argument.

Examples

Query:

SELECT tryBase64Decode('RW5jb2RlZA==') as res, tryBase64Decode('invalid') as res_invalid;
┌─res────────┬─res_invalid─┐
│ clickhouse │             │
└────────────┴─────────────┘

tryBase64URLDecode​

Like base64URLDecode but returns an empty string in case of error.

Syntax

tryBase64URLDecode(encodedUrl)

Parameters

  • encodedURL — String column or constant. If the string is not a valid Base64-encoded value with URL-specific modifications, returns an empty string.

Returned value

  • A string containing the decoded value of the argument.

Examples

Query:

SELECT tryBase64URLDecode('aHR0cDovL2NsaWNraG91c2UuY29t') as res, tryBase64Decode('aHR0cHM6Ly9jbGlja') as res_invalid;
┌─res────────────────────┬─res_invalid─┐
│ https://clickhouse.com │             │
└────────────────────────┴─────────────┘

endsWith​

Returns whether string str ends with suffix.

Syntax

endsWith(str, suffix)

endsWithUTF8​

Returns whether string str ends with suffix, the difference between endsWithUTF8 and endsWith is that endsWithUTF8 match str and suffix by UTF-8 characters.

Syntax

endsWithUTF8(str, suffix)

Example

SELECT endsWithUTF8('中国', '\xbd'), endsWith('中国', '\xbd')

Result:

┌─endsWithUTF8('中国', '½')─┬─endsWith('中国', '½')─┐
│                        0 │                    1 │
└──────────────────────────┴──────────────────────┘

startsWith​

Returns whether string str starts with prefix.

Syntax

startsWith(str, prefix)

Example

SELECT startsWith('Spider-Man', 'Spi');

startsWithUTF8​

Available in version 23.8 and later

Returns whether string str starts with prefix, the difference between startsWithUTF8 and startsWith is that startsWithUTF8 match str and suffix by UTF-8 characters.

Example

SELECT startsWithUTF8('中国', '\xe4'), startsWith('中国', '\xe4')

Result:

┌─startsWithUTF8('中国', '⥩─┬─startsWith('中国', '⥩─┐
│                          0 │                      1 │
└────────────────────────────┴────────────────────────┘

trim​

Removes the specified characters from the start or end of a string. If not specified otherwise, the function removes whitespace (ASCII-character 32).

Syntax

trim([[LEADING|TRAILING|BOTH] trim_character FROM] input_string)

Arguments

  • trim_character — Specified characters for trim. String.
  • input_string — String for trim. String.

Returned value

A string without leading and/or trailing specified characters. String.

Example

SELECT trim(BOTH ' ()' FROM '(   Hello, world!   )');

Result:

┌─trim(BOTH ' ()' FROM '(   Hello, world!   )')─┐
│ Hello, world!                                 │
└───────────────────────────────────────────────┘

trimLeft​

Removes the consecutive occurrences of whitespace (ASCII-character 32) from the start of a string.

Syntax

trimLeft(input_string)

Alias: ltrim(input_string).

Arguments

  • input_string — string to trim. String.

Returned value

A string without leading common whitespaces. String.

Example

SELECT trimLeft('     Hello, world!     ');

Result:

┌─trimLeft('     Hello, world!     ')─┐
│ Hello, world!                       │
└─────────────────────────────────────┘

trimRight​

Removes the consecutive occurrences of whitespace (ASCII-character 32) from the end of a string.

Syntax

trimRight(input_string)

Alias: rtrim(input_string).

Arguments

  • input_string — string to trim. String.

Returned value

A string without trailing common whitespaces. String.

Example

SELECT trimRight('     Hello, world!     ');

Result:

┌─trimRight('     Hello, world!     ')─┐
│      Hello, world!                   │
└──────────────────────────────────────┘

trimBoth​

Removes the consecutive occurrences of whitespace (ASCII-character 32) from both ends of a string.

Syntax

trimBoth(input_string)

Alias: trim(input_string).

Arguments

  • input_string — string to trim. String.

Returned value

A string without leading and trailing common whitespaces. String.

Example

SELECT trimBoth('     Hello, world!     ');

Result:

┌─trimBoth('     Hello, world!     ')─┐
│ Hello, world!                       │
└─────────────────────────────────────┘

CRC32​

Returns the CRC32 checksum of a string using CRC-32-IEEE 802.3 polynomial and initial value 0xffffffff (zlib implementation).

The result type is UInt32.

CRC32IEEE​

Returns the CRC32 checksum of a string, using CRC-32-IEEE 802.3 polynomial.

The result type is UInt32.

CRC64​

Returns the CRC64 checksum of a string, using CRC-64-ECMA polynomial.

The result type is UInt64.

normalizeQuery​

Replaces literals, sequences of literals and complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with placeholder ?.

Syntax

normalizeQuery(x)

Arguments

  • x — Sequence of characters. String.

Returned value

  • Sequence of characters with placeholders. String.

Example

Query:

SELECT normalizeQuery('[1, 2, 3, x]') AS query;

Result:

┌─query────┐
│ [?.., x] │
└──────────┘

normalizeQueryKeepNames​

Replaces literals, sequences of literals with placeholder ? but does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs). This helps better analyze complex query logs.

Syntax

normalizeQueryKeepNames(x)

Arguments

  • x — Sequence of characters. String.

Returned value

  • Sequence of characters with placeholders. String.

Example

Query:

SELECT normalizeQuery('SELECT 1 AS aComplexName123'), normalizeQueryKeepNames('SELECT 1 AS aComplexName123');

Result:

┌─normalizeQuery('SELECT 1 AS aComplexName123')─┬─normalizeQueryKeepNames('SELECT 1 AS aComplexName123')─┐
│ SELECT ? AS `?`                               │ SELECT ? AS aComplexName123                            │
└───────────────────────────────────────────────┴────────────────────────────────────────────────────────┘

normalizedQueryHash​

Returns identical 64bit hash values without the values of literals for similar queries. Can be helpful to analyze query logs.

Syntax

normalizedQueryHash(x)

Arguments

  • x — Sequence of characters. String.

Returned value

Example

Query:

SELECT normalizedQueryHash('SELECT 1 AS `xyz`') != normalizedQueryHash('SELECT 1 AS `abc`') AS res;

Result:

┌─res─┐
│   1 │
└─────┘

normalizedQueryHashKeepNames​

Like normalizedQueryHash it returns identical 64bit hash values without the values of literals for similar queries but it does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with a placeholder before hashing. Can be helpful to analyze query logs.

Syntax

normalizedQueryHashKeepNames(x)

Arguments

  • x — Sequence of characters. String.

Returned value

Example

SELECT normalizedQueryHash('SELECT 1 AS `xyz123`') != normalizedQueryHash('SELECT 1 AS `abc123`') AS normalizedQueryHash;
SELECT normalizedQueryHashKeepNames('SELECT 1 AS `xyz123`') != normalizedQueryHashKeepNames('SELECT 1 AS `abc123`') AS normalizedQueryHashKeepNames;

Result:

┌─normalizedQueryHash─┐
│                   0 │
└─────────────────────┘
┌─normalizedQueryHashKeepNames─┐
│                            1 │
└──────────────────────────────┘

normalizeUTF8NFC​

Converts a string to NFC normalized form, assuming the string is valid UTF8-encoded text.

Syntax

normalizeUTF8NFC(words)

Arguments

  • words — UTF8-encoded input string. String.

Returned value

  • String transformed to NFC normalization form. String.

Example

SELECT length('â'), normalizeUTF8NFC('â') AS nfc, length(nfc) AS nfc_len;

Result:

┌─length('â')─┬─nfc─┬─nfc_len─┐
│           2 │ â   │       2 │
└─────────────┴─────┴─────────┘

normalizeUTF8NFD​

Converts a string to NFD normalized form, assuming the string is valid UTF8-encoded text.

Syntax

normalizeUTF8NFD(words)

Arguments

  • words — UTF8-encoded input string. String.

Returned value

  • String transformed to NFD normalization form. String.

Example

SELECT length('â'), normalizeUTF8NFD('â') AS nfd, length(nfd) AS nfd_len;

Result:

┌─length('â')─┬─nfd─┬─nfd_len─┐
│           2 │ â   │       3 │
└─────────────┴─────┴─────────┘

normalizeUTF8NFKC​

Converts a string to NFKC normalized form, assuming the string is valid UTF8-encoded text.

Syntax

normalizeUTF8NFKC(words)

Arguments

  • words — UTF8-encoded input string. String.

Returned value

  • String transformed to NFKC normalization form. String.

Example

SELECT length('â'), normalizeUTF8NFKC('â') AS nfkc, length(nfkc) AS nfkc_len;

Result:

┌─length('â')─┬─nfkc─┬─nfkc_len─┐
│           2 │ â    │        2 │
└─────────────┴──────┴──────────┘

normalizeUTF8NFKD​

Converts a string to NFKD normalized form, assuming the string is valid UTF8-encoded text.

Syntax

normalizeUTF8NFKD(words)

Arguments

  • words — UTF8-encoded input string. String.

Returned value

  • String transformed to NFKD normalization form. String.

Example

SELECT length('â'), normalizeUTF8NFKD('â') AS nfkd, length(nfkd) AS nfkd_len;

Result:

┌─length('â')─┬─nfkd─┬─nfkd_len─┐
│           2 │ â    │        3 │
└─────────────┴──────┴──────────┘

encodeXMLComponent​

Escapes characters with special meaning in XML such that they can afterwards be place into a XML text node or attribute.

The following characters are replaced: <, &, >, ", '. Also see the list of XML and HTML character entity references.

Syntax

encodeXMLComponent(x)

Arguments

  • x — An input string. String.

Returned value

Example

SELECT encodeXMLComponent('Hello, "world"!');
SELECT encodeXMLComponent('<123>');
SELECT encodeXMLComponent('&clickhouse');
SELECT encodeXMLComponent('\'foo\'');

Result:

Hello, &quot;world&quot;!
&lt;123&gt;
&amp;clickhouse
&apos;foo&apos;

decodeXMLComponent​

Un-escapes substrings with special meaning in XML. These substrings are: &quot; &amp; &apos; &gt; &lt;

This function also replaces numeric character references with Unicode characters. Both decimal (like &#10003;) and hexadecimal (&#x2713;) forms are supported.

Syntax

decodeXMLComponent(x)

Arguments

  • x — An input string. String.

Returned value

  • The un-escaped string. String.

Example

SELECT decodeXMLComponent('&apos;foo&apos;');
SELECT decodeXMLComponent('&lt; &#x3A3; &gt;');

Result:

'foo'
< Σ >

decodeHTMLComponent​

Un-escapes substrings with special meaning in HTML. For example: &hbar; &gt; &diamondsuit; &heartsuit; &lt; etc.

This function also replaces numeric character references with Unicode characters. Both decimal (like &#10003;) and hexadecimal (&#x2713;) forms are supported.

Syntax

decodeHTMLComponent(x)

Arguments

  • x — An input string. String.

Returned value

  • The un-escaped string. String.

Example

SELECT decodeHTMLComponent(''CH');
SELECT decodeHTMLComponent('I&heartsuit;ClickHouse');

Result:

'CH'
I♥ClickHouse'

extractTextFromHTML​

This function extracts plain text from HTML or XHTML.

It does not conform 100% to the HTML, XML or XHTML specification but the implementation is reasonably accurate and fast. The rules are the following:

  1. Comments are skipped. Example: <!-- test -->. Comment must end with -->. Nested comments are disallowed. Note: constructions like <!--> and <!---> are not valid comments in HTML but they are skipped by other rules.
  2. CDATA is pasted verbatim. Note: CDATA is XML/XHTML-specific and processed on a "best-effort" basis.
  3. script and style elements are removed with all their content. Note: it is assumed that closing tag cannot appear inside content. For example, in JS string literal has to be escaped like "<\/script>". Note: comments and CDATA are possible inside script or style - then closing tags are not searched inside CDATA. Example: <script><![CDATA[</script>]]></script>. But they are still searched inside comments. Sometimes it becomes complicated: <script>var x = "<!--"; </script> var y = "-->"; alert(x + y);</script> Note: script and style can be the names of XML namespaces - then they are not treated like usual script or style elements. Example: <script:a>Hello</script:a>. Note: whitespaces are possible after closing tag name: </script > but not before: < / script>.
  4. Other tags or tag-like elements are skipped without inner content. Example: <a>.</a> Note: it is expected that this HTML is illegal: <a test=">"></a> Note: it also skips something like tags: <>, <!>, etc. Note: tag without end is skipped to the end of input: <hello
  5. HTML and XML entities are not decoded. They must be processed by separate function.
  6. Whitespaces in the text are collapsed or inserted by specific rules.
    • Whitespaces at the beginning and at the end are removed.
    • Consecutive whitespaces are collapsed.
    • But if the text is separated by other elements and there is no whitespace, it is inserted.
    • It may cause unnatural examples: Hello<b>world</b>, Hello<!-- -->world - there is no whitespace in HTML, but the function inserts it. Also consider: Hello<p>world</p>, Hello<br>world. This behavior is reasonable for data analysis, e.g. to convert HTML to a bag of words.
  7. Also note that correct handling of whitespaces requires the support of <pre></pre> and CSS display and white-space properties.

Syntax

extractTextFromHTML(x)

Arguments

Returned value

Example

The first example contains several tags and a comment and also shows whitespace processing. The second example shows CDATA and script tag processing. In the third example text is extracted from the full HTML response received by the url function.

SELECT extractTextFromHTML(' <p> A text <i>with</i><b>tags</b>. <!-- comments --> </p> ');
SELECT extractTextFromHTML('<![CDATA[The content within <b>CDATA</b>]]> <script>alert("Script");</script>');
SELECT extractTextFromHTML(html) FROM url('http://www.donothingfor2minutes.com/', RawBLOB, 'html String');

Result:

A text with tags .
The content within <b>CDATA</b>
Do Nothing for 2 Minutes 2:00 &nbsp;

ascii​

Returns the ASCII code point (as Int32) of the first character of string s.

If s is empty, the result is 0. If the first character is not an ASCII character or not part of the Latin-1 supplement range of UTF-16, the result is undefined.

Syntax

ascii(s)

soundex​

Returns the Soundex code of a string.

Syntax

soundex(val)

Arguments

Returned value

  • The Soundex code of the input value. String

Example

select soundex('aksel');

Result:

┌─soundex('aksel')─┐
│ A240             │
└──────────────────┘

punycodeEncode​

Returns the Punycode representation of a string. The string must be UTF8-encoded, otherwise the behavior is undefined.

Syntax

punycodeEncode(val)

Arguments

Returned value

  • A Punycode representation of the input value. String

Example

select punycodeEncode('München');

Result:

┌─punycodeEncode('München')─┐
│ Mnchen-3ya                │
└───────────────────────────┘

punycodeDecode​

Returns the UTF8-encoded plaintext of a Punycode-encoded string. If no valid Punycode-encoded string is given, an exception is thrown.

Syntax

punycodeEncode(val)

Arguments

  • val — Punycode-encoded string. String

Returned value

  • The plaintext of the input value. String

Example

select punycodeDecode('Mnchen-3ya');

Result:

┌─punycodeDecode('Mnchen-3ya')─┐
│ München                      │
└──────────────────────────────┘

tryPunycodeDecode​

Like punycodeDecode but returns an empty string if no valid Punycode-encoded string is given.

idnaEncode​

Returns the ASCII representation (ToASCII algorithm) of a domain name according to the Internationalized Domain Names in Applications (IDNA) mechanism. The input string must be UTF-encoded and translatable to an ASCII string, otherwise an exception is thrown. Note: No percent decoding or trimming of tabs, spaces or control characters is performed.

Syntax

idnaEncode(val)

Arguments

Returned value

  • A ASCII representation according to the IDNA mechanism of the input value. String

Example

select idnaEncode('straße.münchen.de');

Result:

┌─idnaEncode('straße.münchen.de')─────┐
│ xn--strae-oqa.xn--mnchen-3ya.de     │
└─────────────────────────────────────┘

tryIdnaEncode​

Like idnaEncode but returns an empty string in case of an error instead of throwing an exception.

idnaDecode​

Returns the Unicode (UTF-8) representation (ToUnicode algorithm) of a domain name according to the Internationalized Domain Names in Applications (IDNA) mechanism. In case of an error (e.g. because the input is invalid), the input string is returned. Note that repeated application of idnaEncode() and idnaDecode() does not necessarily return the original string due to case normalization.

Syntax

idnaDecode(val)

Arguments

Returned value

  • A Unicode (UTF-8) representation according to the IDNA mechanism of the input value. String

Example

select idnaDecode('xn--strae-oqa.xn--mnchen-3ya.de');

Result:

┌─idnaDecode('xn--strae-oqa.xn--mnchen-3ya.de')─┐
│ straße.münchen.de                             │
└───────────────────────────────────────────────┘

byteHammingDistance​

Calculates the hamming distance between two byte strings.

Syntax

byteHammingDistance(string1, string2)

Examples

SELECT byteHammingDistance('karolin', 'kathrin');

Result:

┌─byteHammingDistance('karolin', 'kathrin')─┐
│                                         3 │
└───────────────────────────────────────────┘

Alias: mismatches

stringJaccardIndex​

Calculates the Jaccard similarity index between two byte strings.

Syntax

stringJaccardIndex(string1, string2)

Examples

SELECT stringJaccardIndex('clickhouse', 'mouse');

Result:

┌─stringJaccardIndex('clickhouse', 'mouse')─┐
│                                       0.4 │
└───────────────────────────────────────────┘

stringJaccardIndexUTF8​

Like stringJaccardIndex but for UTF8-encoded strings.

editDistance​

Calculates the edit distance between two byte strings.

Syntax

editDistance(string1, string2)

Examples

SELECT editDistance('clickhouse', 'mouse');

Result:

┌─editDistance('clickhouse', 'mouse')─┐
│                                   6 │
└─────────────────────────────────────┘

Alias: levenshteinDistance

editDistanceUTF8​

Calculates the edit distance between two UTF8 strings.

Syntax

editDistanceUTF8(string1, string2)

Examples

SELECT editDistanceUTF8('我是谁', '我是我');

Result:

┌─editDistanceUTF8('我是谁', '我是我')──┐
│                                   1 │
└─────────────────────────────────────┘

Alias: levenshteinDistanceUTF8

damerauLevenshteinDistance​

Calculates the Damerau-Levenshtein distance between two byte strings.

Syntax

damerauLevenshteinDistance(string1, string2)

Examples

SELECT damerauLevenshteinDistance('clickhouse', 'mouse');

Result:

┌─damerauLevenshteinDistance('clickhouse', 'mouse')─┐
│                                                 6 │
└───────────────────────────────────────────────────┘

jaroSimilarity​

Calculates the Jaro similarity between two byte strings.

Syntax

jaroSimilarity(string1, string2)

Examples

SELECT jaroSimilarity('clickhouse', 'click');

Result:

┌─jaroSimilarity('clickhouse', 'click')─┐
│                    0.8333333333333333 │
└───────────────────────────────────────┘

jaroWinklerSimilarity​

Calculates the Jaro-Winkler similarity between two byte strings.

Syntax

jaroWinklerSimilarity(string1, string2)

Examples

SELECT jaroWinklerSimilarity('clickhouse', 'click');

Result:

┌─jaroWinklerSimilarity('clickhouse', 'click')─┐
│                           0.8999999999999999 │
└──────────────────────────────────────────────┘

initcap​

Convert the first letter of each word to upper case and the rest to lower case. Words are sequences of alphanumeric characters separated by non-alphanumeric characters.

Note

Because initCap converts only the first letter of each word to upper case you may observe unexpected behaviour for words containing apostrophes or capital letters. For example:

SELECT initCap('mother''s daughter'), initCap('joe McAdam');

will return

┌─initCap('mother\'s daughter')─┬─initCap('joe McAdam')─┐
│ Mother'S Daughter             │ Joe Mcadam            │
└───────────────────────────────┴───────────────────────┘

This is a known behaviour, with no plans currently to fix it.

Syntax

initcap(val)

Arguments

Returned value

  • val with the first letter of each word converted to upper case. String.

Example

Query:

SELECT initcap('building for fast');

Result:

┌─initcap('building for fast')─┐
│ Building For Fast            │
└──────────────────────────────┘

initcapUTF8​

Like initcap, initcapUTF8 converts the first letter of each word to upper case and the rest to lower case. Assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.

Note

This function does not detect the language, e.g. for Turkish the result might not be exactly correct (i/İ vs. i/I). If the length of the UTF-8 byte sequence is different for upper and lower case of a code point, the result may be incorrect for this code point.

Syntax

initcapUTF8(val)

Arguments

Returned value

  • val with the first letter of each word converted to upper case. String.

Example

Query:

SELECT initcapUTF8('не тормозит');

Result:

┌─initcapUTF8('не тормозит')─┐
│ Не Тормозит                │
└────────────────────────────┘

firstLine​

Returns the first line from a multi-line string.

Syntax

firstLine(val)

Arguments

Returned value

  • The first line of the input value or the whole value if there is no line separators. String

Example

select firstLine('foo\nbar\nbaz');

Result:

┌─firstLine('foo\nbar\nbaz')─┐
│ foo                        │
└────────────────────────────┘