Relational Data - Functions - Splitting Merging Functions

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splitByChar

Splits a string into substrings separated by a specified character. Uses a constant string separator which consists of exactly one character. Returns an array of selected substrings. Empty substrings may be selected if the separator occurs at the beginning or end of the string, or if there are multiple consecutive separators.

Syntax 

splitByChar(separator, s[, max_substrings]))

Arguments

  • separator — The separator which should contain exactly one character. String.
  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. If max_substrings > 0, the returned array will contain at most max_substrings substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Empty substrings may be selected when:

  • A separator occurs at the beginning or end of the string;
  • There are multiple consecutive separators;
  • The original string s is empty.

The behavior of parameter max_substrings changed starting with ClickHouse v22.11. In versions older than that, max_substrings > 0 meant that max_substring-many splits were performed and that the remainder of the string was returned as the final element of the list. For example, - in v22.10: SELECT splitByChar('=', 'a=b=c=d', 2); returned ['a','b','c=d'] - in v22.11: SELECT splitByChar('=', 'a=b=c=d', 2); returned ['a','b']

A behavior similar to ClickHouse pre-v22.11 can be achieved by setting splitby_max_substrings_includes_remaining_string SELECT splitByChar('=', 'a=b=c=d', 2) SETTINGS splitby_max_substrings_includes_remaining_string = 1 -- ['a', 'b=c=d']


Example 

SELECT splitByChar(',', '1,2,3,abcde');

Result: 

┌─splitByChar(',', '1,2,3,abcde')─┐
│ ['1','2','3','abcde']           │
└─────────────────────────────────┘

splitByString

Splits a string into substrings separated by a string. It uses a constant string separator of multiple characters as the separator. If the string separator is empty, it will split the string s into an array of single characters.

Syntax 

splitByString(separator, s[, max_substrings]))

Arguments

  • separator — The separator. String.
  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. When max_substrings > 0, the returned substrings will be no more than max_substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Empty substrings may be selected when:

  • A non-empty separator occurs at the beginning or end of the string;
  • There are multiple consecutive non-empty separators;
  • The original string s is empty while the separator is not empty.

Setting splitby_max_substrings_includes_remaining_string (default: 0) controls if the remaining string is included in the last element of the result array when argument max_substrings > 0.


Example 

SELECT splitByString(', ', '1, 2 3, 4,5, abcde');

Result: 

┌─splitByString(', ', '1, 2 3, 4,5, abcde')─┐
│ ['1','2 3','4,5','abcde']                 │
└───────────────────────────────────────────┘
SELECT splitByString('', 'abcde');

Result: 

┌─splitByString('', 'abcde')─┐
│ ['a','b','c','d','e']      │
└────────────────────────────┘

splitByRegexp

Splits a string into substrings separated by a regular expression. It uses a regular expression string regexp as the separator. If the regexp is empty, it will split the string s into an array of single characters. If no match is found for this regular expression, the string s won’t be split.

Syntax 

splitByRegexp(regexp, s[, max_substrings]))

Arguments

  • regexp — Regular expression. Constant. String or FixedString.
  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. When max_substrings > 0, the returned substrings will be no more than max_substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Empty substrings may be selected when:

  • A non-empty regular expression match occurs at the beginning or end of the string;
  • There are multiple consecutive non-empty regular expression matches;
  • The original string s is empty while the regular expression is not empty.

Setting splitby_max_substrings_includes_remaining_string (default: 0) controls if the remaining string is included in the last element of the result array when argument max_substrings > 0.


Example 

SELECT splitByRegexp('\\d+', 'a12bc23de345f');

Result: 

┌─splitByRegexp('\\d+', 'a12bc23de345f')─┐
│ ['a','bc','de','f']                    │
└────────────────────────────────────────┘
SELECT splitByRegexp('', 'abcde');

Result: 

┌─splitByRegexp('', 'abcde')─┐
│ ['a','b','c','d','e']      │
└────────────────────────────┘

splitByWhitespace

Splits a string into substrings separated by whitespace characters. Returns an array of selected substrings.

Syntax 

splitByWhitespace(s[, max_substrings]))

Arguments

  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. When max_substrings > 0, the returned substrings will be no more than max_substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Setting splitby_max_substrings_includes_remaining_string (default: 0) controls if the remaining string is included in the last element of the result array when argument max_substrings > 0.


Example 

SELECT splitByWhitespace('  1!  a,  b.  ');

Result: 

┌─splitByWhitespace('  1!  a,  b.  ')─┐
│ ['1!','a,','b.']                    │
└─────────────────────────────────────┘

splitByNonAlpha

Splits a string into substrings separated by whitespace and punctuation characters. Returns an array of selected substrings.

Syntax 

splitByNonAlpha(s[, max_substrings]))

Arguments

  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. When max_substrings > 0, the returned substrings will be no more than max_substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Setting splitby_max_substrings_includes_remaining_string (default: 0) controls if the remaining string is included in the last element of the result array when argument max_substrings > 0.


Example 

SELECT splitByNonAlpha('  1!  a,  b.  ');
┌─splitByNonAlpha('  1!  a,  b.  ')─┐
│ ['1','a','b']                     │
└───────────────────────────────────┘

arrayStringConcat

Concatenates string representations of values listed in the array with the separator. separator is an optional parameter: a constant string, set to an empty string by default. Returns the string.

Syntax 

arrayStringConcat(arr\[, separator\])

Example 

SELECT arrayStringConcat(['12/05/2021', '12:50:00'], ' ') AS DateString;

Result: 

┌─DateString──────────┐
│ 12/05/2021 12:50:00 │
└─────────────────────┘

alphaTokens

Selects substrings of consecutive bytes from the ranges a-z and A-Z.Returns an array of substrings.

Syntax 

alphaTokens(s[, max_substrings]))

Alias: splitByAlpha

Arguments

  • s — The string to split. String.
  • max_substrings — An optional Int64 defaulting to 0. When max_substrings > 0, the returned substrings will be no more than max_substrings, otherwise the function will return as many substrings as possible.

Returned value(s)

Setting splitby_max_substrings_includes_remaining_string (default: 0) controls if the remaining string is included in the last element of the result array when argument max_substrings > 0.


Example 

SELECT alphaTokens('abca1abc');
┌─alphaTokens('abca1abc')─┐
│ ['abca','abc']          │
└─────────────────────────┘

extractAllGroups

Extracts all groups from non-overlapping substrings matched by a regular expression.

Syntax 

extractAllGroups(text, regexp)

Arguments

Returned values

  • If the function finds at least one matching group, it returns Array(Array(String)) column, clustered by group_id (1 to N, where N is number of capturing groups in regexp). If there is no matching group, it returns an empty array. Array.

Example 

SELECT extractAllGroups('abc=123, 8="hkl"', '("[^"]+"|\\w+)=("[^"]+"|\\w+)');

Result: 

┌─extractAllGroups('abc=123, 8="hkl"', '("[^"]+"|\\w+)=("[^"]+"|\\w+)')─┐
│ [['abc','123'],['8','"hkl"']]                                         │
└───────────────────────────────────────────────────────────────────────┘

ngrams

Splits a UTF-8 string into n-grams of ngramsize symbols.

Syntax 

ngrams(string, ngramsize)

Arguments

Returned values

Example 

SELECT ngrams('ClickHouse', 3);

Result: 

┌─ngrams('ClickHouse', 3)───────────────────────────┐
│ ['Cli','lic','ick','ckH','kHo','Hou','ous','use'] │
└───────────────────────────────────────────────────┘

tokens

Splits a string into tokens using non-alphanumeric ASCII characters as separators.

Arguments

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

Returned value

  • The resulting array of tokens from input string. Array.

Example 

SELECT tokens('test1,;\\ test2,;\\ test3,;\\   test4') AS tokens;

Result: 

┌─tokens────────────────────────────┐
│ ['test1','test2','test3','test4'] │
└───────────────────────────────────┘
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