ClickHouse/docs/en/sql-reference/functions/string-search-functions.md

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/en/sql-reference/functions/string-search-functions	160	Searching in Strings

Functions for Searching in Strings

All functions in this section search case-sensitively by default. Case-insensitive search is usually provided by separate function variants.

:::note Case-insensitive search follows the lowercase-uppercase rules of the English language. E.g. Uppercased i in the English language is I whereas in the Turkish language it is İ - results for languages other than English may be unexpected. :::

Functions in this section also assume that the searched string (referred to in this section as haystack) and the search string (referred to in this section as needle) are single-byte encoded text. If this assumption is violated, no exception is thrown and results are undefined. Search with UTF-8 encoded strings is usually provided by separate function variants. Likewise, if a UTF-8 function variant is used and the input strings are not UTF-8 encoded text, no exception is thrown and the results are undefined. Note that no automatic Unicode normalization is performed, however you can use the normalizeUTF8*() functions for that.

General strings functions and functions for replacing in strings are described separately.

position

Returns the position (in bytes, starting at 1) of a substring needle in a string haystack.

Syntax

position(haystack, needle[, start_pos])

Alias:

• position(needle IN haystack)

Arguments

• haystack — String in which the search is performed. String.
• needle — Substring to be searched. String.
• start_pos – Position (1-based) in haystack at which the search starts. UInt. Optional.

Returned values

• Starting position in bytes and counting from 1, if the substring was found.
• 0, if the substring was not found.

If substring needle is empty, these rules apply:

• if no start_pos was specified: return 1
• if start_pos = 0: return 1
• if start_pos >= 1 and start_pos <= length(haystack) + 1: return start_pos
• otherwise: return 0

The same rules also apply to functions locate, positionCaseInsensitive, positionUTF8 and positionCaseInsensitiveUTF8.

Type: Integer.

Examples

Query:

SELECT position('Hello, world!', '!');

Result:

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

Example with start_pos argument:

Query:

SELECT
    position('Hello, world!', 'o', 1),
    position('Hello, world!', 'o', 7)

Result:

┌─position('Hello, world!', 'o', 1)─┬─position('Hello, world!', 'o', 7)─┐
│                                 5 │                                 9 │
└───────────────────────────────────┴───────────────────────────────────┘

Example for needle IN haystack syntax:

Query:

SELECT 6 = position('/' IN s) FROM (SELECT 'Hello/World' AS s);

Result:

┌─equals(6, position(s, '/'))─┐
│                           1 │
└─────────────────────────────┘

Examples with empty needle substring:

Query:

SELECT
    position('abc', ''),
    position('abc', '', 0),
    position('abc', '', 1),
    position('abc', '', 2),
    position('abc', '', 3),
    position('abc', '', 4),
    position('abc', '', 5)

Result:

┌─position('abc', '')─┬─position('abc', '', 0)─┬─position('abc', '', 1)─┬─position('abc', '', 2)─┬─position('abc', '', 3)─┬─position('abc', '', 4)─┬─position('abc', '', 5)─┐
│                   1 │                      1 │                      1 │                      2 │                      3 │                      4 │                      0 │
└─────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┘

locate

Like position but with arguments haystack and locate switched.

The behavior of this function depends on the ClickHouse version:

• in versions < v24.3, locate was an alias of function position and accepted arguments (haystack, needle[, start_pos]).
• in versions >= 24.3,, locate is an individual function (for better compatibility with MySQL) and accepts arguments (needle, haystack[, start_pos]). The previous behavior can be restored using setting function_locate_has_mysql_compatible_argument_order = false;

Syntax

locate(needle, haystack[, start_pos])

positionCaseInsensitive

A case insensitive invariant of position.

Example

Query:

SELECT position('Hello, world!', 'hello');

Result:

┌─position('Hello, world!', 'hello')─┐
│                                  0 │
└────────────────────────────────────┘

positionUTF8

Like position but assumes haystack and needle are UTF-8 encoded strings.

Examples

Function positionUTF8 correctly counts character ö (represented by two points) as a single Unicode codepoint:

Query:

SELECT positionUTF8('Motörhead', 'r');

Result:

┌─position('Motörhead', 'r')─┐
│                          5 │
└────────────────────────────┘

positionCaseInsensitiveUTF8

Like positionUTF8 but searches case-insensitively.

multiSearchAllPositions

Like position but returns an array of positions (in bytes, starting at 1) for multiple needle substrings in a haystack string.

:::note All multiSearch*() functions only support up to 2⁸ needles. :::

Syntax

multiSearchAllPositions(haystack, [needle1, needle2, ..., needleN])

Arguments

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned values

• Array of the starting position in bytes and counting from 1, if the substring was found.
• 0, if the substring was not found.

Example

Query:

SELECT multiSearchAllPositions('Hello, World!', ['hello', '!', 'world']);

Result:

┌─multiSearchAllPositions('Hello, World!', ['hello', '!', 'world'])─┐
│ [0,13,0]                                                          │
└───────────────────────────────────────────────────────────────────┘

multiSearchAllPositionsCaseInsensitive

Like multiSearchAllPositions but ignores case.

Syntax

multiSearchAllPositionsCaseInsensitive(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned value

• Array of the starting position in bytes and counting from 1 (if the substring was found).
• 0 if the substring was not found.

Example

Query:

SELECT multiSearchAllPositionsCaseInsensitive('ClickHouse',['c','h']);

Result:

["1","6"]

multiSearchAllPositionsUTF8

Like multiSearchAllPositions but assumes haystack and the needle substrings are UTF-8 encoded strings.

Syntax

multiSearchAllPositionsUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 encoded string in which the search is performed. String.
• needle — UTF-8 encoded substrings to be searched. Array.

Returned value

• Array of the starting position in bytes and counting from 1 (if the substring was found).
• 0 if the substring was not found.

Example

Given ClickHouse as a UTF-8 string, find the positions of C (\x43) and H (\x48).

Query:

SELECT multiSearchAllPositionsUTF8('\x43\x6c\x69\x63\x6b\x48\x6f\x75\x73\x65',['\x43','\x48']);

Result:

["1","6"]

multiSearchAllPositionsCaseInsensitiveUTF8

Like multiSearchAllPositionsUTF8 but ignores case.

Syntax

multiSearchAllPositionsCaseInsensitiveUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 encoded string in which the search is performed. String.
• needle — UTF-8 encoded substrings to be searched. Array.

Returned value

• Array of the starting position in bytes and counting from 1 (if the substring was found).
• 0 if the substring was not found.

Example

Given ClickHouse as a UTF-8 string, find the positions of c (\x63) and h (\x68).

Query:

SELECT multiSearchAllPositionsCaseInsensitiveUTF8('\x43\x6c\x69\x63\x6b\x48\x6f\x75\x73\x65',['\x63','\x68']);

Result:

["1","6"]

multiSearchFirstPosition

Like position but returns the leftmost offset in a haystack string which matches any of multiple needle strings.

Functions multiSearchFirstPositionCaseInsensitive, multiSearchFirstPositionUTF8 and multiSearchFirstPositionCaseInsensitiveUTF8 provide case-insensitive and/or UTF-8 variants of this function.

Syntax

multiSearchFirstPosition(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned value

• Leftmost offset in a haystack string which matches any of multiple needle strings.
• 0, if there was no match.

Example

Query:

SELECT multiSearchFirstPosition('Hello World',['llo', 'Wor', 'ld']);

Result:

3

multiSearchFirstPositionCaseInsensitive

Like multiSearchFirstPosition but ignores case.

Syntax

multiSearchFirstPositionCaseInsensitive(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Array of substrings to be searched. Array.

Returned value

• Leftmost offset in a haystack string which matches any of multiple needle strings.
• 0, if there was no match.

Example

Query:

SELECT multiSearchFirstPositionCaseInsensitive('HELLO WORLD',['wor', 'ld', 'ello']);

Result:

2

multiSearchFirstPositionUTF8

Like multiSearchFirstPosition but assumes haystack and needle to be UTF-8 strings.

Syntax

multiSearchFirstPositionUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — Array of UTF-8 substrings to be searched. Array.

Returned value

• Leftmost offset in a haystack string which matches any of multiple needle strings.
• 0, if there was no match.

Example

Find the leftmost offset in UTF-8 string hello world which matches any of the given needles.

Query:

SELECT multiSearchFirstPositionUTF8('\x68\x65\x6c\x6c\x6f\x20\x77\x6f\x72\x6c\x64',['wor', 'ld', 'ello']);

Result:

2

multiSearchFirstPositionCaseInsensitiveUTF8

Like multiSearchFirstPosition but assumes haystack and needle to be UTF-8 strings and ignores case.

Syntax

multiSearchFirstPositionCaseInsensitiveUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — Array of UTF-8 substrings to be searched. Array

Returned value

• Leftmost offset in a haystack string which matches any of multiple needle strings, ignoring case.
• 0, if there was no match.

Example

Find the leftmost offset in UTF-8 string HELLO WORLD which matches any of the given needles.

Query:

SELECT multiSearchFirstPositionCaseInsensitiveUTF8('\x48\x45\x4c\x4c\x4f\x20\x57\x4f\x52\x4c\x44',['wor', 'ld', 'ello']);

Result:

2

multiSearchFirstIndex

Returns the index i (starting from 1) of the leftmost found needle_i in the string haystack and 0 otherwise.

Functions multiSearchFirstIndexCaseInsensitive, multiSearchFirstIndexUTF8 and multiSearchFirstIndexCaseInsensitiveUTF8 provide case-insensitive and/or UTF-8 variants of this function.

Syntax

multiSearchFirstIndex(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned value

• index (starting from 1) of the leftmost found needle.
• 0, if there was no match.

Example

Query:

SELECT multiSearchFirstIndex('Hello World',['World','Hello']);

Result:

1

multiSearchFirstIndexCaseInsensitive

Returns the index i (starting from 1) of the leftmost found needle_i in the string haystack and 0 otherwise. Ignores case.

Syntax

multiSearchFirstIndexCaseInsensitive(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned value

• index (starting from 1) of the leftmost found needle.
• 0, if there was no match.

Example

Query:

SELECT multiSearchFirstIndexCaseInsensitive('hElLo WoRlD',['World','Hello']);

Result:

1

multiSearchFirstIndexUTF8

Returns the index i (starting from 1) of the leftmost found needle_i in the string haystack and 0 otherwise. Assumes haystack and needle are UTF-8 encoded strings.

Syntax

multiSearchFirstIndexUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — Array of UTF-8 substrings to be searched. Array

Returned value

• index (starting from 1) of the leftmost found needle.
• 0, if there was no match.

Example

Given Hello World as a UTF-8 string, find the first index of UTF-8 strings Hello and World.

Query:

SELECT multiSearchFirstIndexUTF8('\x48\x65\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64',['\x57\x6f\x72\x6c\x64','\x48\x65\x6c\x6c\x6f']);

Result:

1

multiSearchFirstIndexCaseInsensitiveUTF8

Returns the index i (starting from 1) of the leftmost found needle_i in the string haystack and 0 otherwise. Assumes haystack and needle are UTF-8 encoded strings. Ignores case.

Syntax

multiSearchFirstIndexCaseInsensitiveUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — Array of UTF-8 substrings to be searched. Array.

Returned value

• index (starting from 1) of the leftmost found needle.
• 0, if there was no match.

Example

Given HELLO WORLD as a UTF-8 string, find the first index of UTF-8 strings hello and world.

Query:

SELECT multiSearchFirstIndexCaseInsensitiveUTF8('\x48\x45\x4c\x4c\x4f\x20\x57\x4f\x52\x4c\x44',['\x68\x65\x6c\x6c\x6f','\x77\x6f\x72\x6c\x64']);

Result:

1

multiSearchAny

Returns 1, if at least one string needle_i matches the string haystack and 0 otherwise.

Functions multiSearchAnyCaseInsensitive, multiSearchAnyUTF8 and []multiSearchAnyCaseInsensitiveUTF8](#multiSearchAnyCaseInsensitiveUTF8) provide case-insensitive and/or UTF-8 variants of this function.

Syntax

multiSearchAny(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array.

Returned value

• 1, if there was at least one match.
• 0, if there was not at least one match.

Example

Query:

SELECT multiSearchAny('ClickHouse',['C','H']);

Result:

1

multiSearchAnyCaseInsensitive

Like multiSearchAny but ignores case.

Syntax

multiSearchAnyCaseInsensitive(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — String in which the search is performed. String.
• needle — Substrings to be searched. Array

Returned value

• 1, if there was at least one case-insensitive match.
• 0, if there was not at least one case-insensitive match.

Example

Query:

SELECT multiSearchAnyCaseInsensitive('ClickHouse',['c','h']);

Result:

1

multiSearchAnyUTF8

Like multiSearchAny but assumes haystack and the needle substrings are UTF-8 encoded strings.

Syntax*

multiSearchAnyUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — UTF-8 substrings to be searched. Array.

Returned value

• 1, if there was at least one match.
• 0, if there was not at least one match.

Example

Given ClickHouse as a UTF-8 string, check if there are any C ('\x43') or H ('\x48') letters in the word.

Query:

SELECT multiSearchAnyUTF8('\x43\x6c\x69\x63\x6b\x48\x6f\x75\x73\x65',['\x43','\x48']);

Result:

1

multiSearchAnyCaseInsensitiveUTF8

Like multiSearchAnyUTF8 but ignores case.

Syntax*

multiSearchAnyCaseInsensitiveUTF8(haystack, [needle1, needle2, ..., needleN])

Parameters

• haystack — UTF-8 string in which the search is performed. String.
• needle — UTF-8 substrings to be searched. Array

Returned value

• 1, if there was at least one case-insensitive match.
• 0, if there was not at least one case-insensitive match.

Example

Given ClickHouse as a UTF-8 string, check if there is any letter h(\x68) in the word, ignoring case.

Query:

SELECT multiSearchAnyCaseInsensitiveUTF8('\x43\x6c\x69\x63\x6b\x48\x6f\x75\x73\x65',['\x68']);

Result:

1

match

Returns whether string haystack matches the regular expression pattern in re2 regular syntax.

Matching is based on UTF-8, e.g. . matches the Unicode code point ¥ which is represented in UTF-8 using two bytes. The regular expression must not contain null bytes. If the haystack or the pattern are not valid UTF-8, then the behavior is undefined.

Unlike re2's default behavior, . matches line breaks. To disable this, prepend the pattern with (?-s).

If you only want to search substrings in a string, you can use functions like or position instead - they work much faster than this function.

Syntax

match(haystack, pattern)

Alias: haystack REGEXP pattern operator

multiMatchAny

Like match but returns 1 if at least one of the patterns match and 0 otherwise.

:::note Functions in the multi[Fuzzy]Match*() family use the the (Vectorscan)[https://github.com/VectorCamp/vectorscan] library. As such, they are only enabled if ClickHouse is compiled with support for vectorscan.

To turn off all functions that use hyperscan, use setting SET allow_hyperscan = 0;.

Due to restrictions of vectorscan, the length of the haystack string must be less than 2³² bytes.

Hyperscan is generally vulnerable to regular expression denial of service (ReDoS) attacks (e.g. see (here)[https://www.usenix.org/conference/usenixsecurity22/presentation/turonova], (here)[https://doi.org/10.1007/s10664-021-10033-1] and (here)[https://doi.org/10.1145/3236024.3236027]. Users are adviced to check the provided patterns carefully. :::

If you only want to search multiple substrings in a string, you can use function multiSearchAny instead - it works much faster than this function.

Syntax

multiMatchAny(haystack, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

multiMatchAnyIndex

Like multiMatchAny but returns any index that matches the haystack.

Syntax

multiMatchAnyIndex(haystack, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

multiMatchAllIndices

Like multiMatchAny but returns the array of all indices that match the haystack in any order.

Syntax

multiMatchAllIndices(haystack, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

multiFuzzyMatchAny

Like multiMatchAny but returns 1 if any pattern matches the haystack within a constant edit distance. This function relies on the experimental feature of hyperscan library, and can be slow for some corner cases. The performance depends on the edit distance value and patterns used, but it's always more expensive compared to a non-fuzzy variants.

:::note multiFuzzyMatch*() function family do not support UTF-8 regular expressions (it threats them as a sequence of bytes) due to restrictions of hyperscan. :::

Syntax

multiFuzzyMatchAny(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

multiFuzzyMatchAnyIndex

Like multiFuzzyMatchAny but returns any index that matches the haystack within a constant edit distance.

Syntax

multiFuzzyMatchAnyIndex(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

multiFuzzyMatchAllIndices

Like multiFuzzyMatchAny but returns the array of all indices in any order that match the haystack within a constant edit distance.

Syntax

multiFuzzyMatchAllIndices(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])

extract

Extracts a fragment of a string using a regular expression. If haystack does not match the pattern regex, an empty string is returned.

For regex without subpatterns, the function uses the fragment that matches the entire regex. Otherwise, it uses the fragment that matches the first subpattern.

Syntax

extract(haystack, pattern)

extractAll

Extracts all fragments of a string using a regular expression. If haystack does not match the pattern regex, an empty string is returned.

Returns an array of strings consisting of all matches of the regex.

The behavior with respect to subpatterns is the same as in function extract.

Syntax

extractAll(haystack, pattern)

extractAllGroupsHorizontal

Matches all groups of the haystack string using the pattern regular expression. Returns an array of arrays, where the first array includes all fragments matching the first group, the second array - matching the second group, etc.

This function is slower than extractAllGroupsVertical.

Syntax

extractAllGroupsHorizontal(haystack, pattern)

Arguments

• haystack — Input string. Type: String.
• pattern — Regular expression with re2 syntax. Must contain groups, each group enclosed in parentheses. If pattern contains no groups, an exception is thrown. Type: String.

Returned value

• Type: Array.

If haystack does not match the pattern regex, an array of empty arrays is returned.

Example

SELECT extractAllGroupsHorizontal('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)');

Result:

┌─extractAllGroupsHorizontal('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)')─┐
│ [['abc','def','ghi'],['111','222','333']]                                                │
└──────────────────────────────────────────────────────────────────────────────────────────┘

extractAllGroupsVertical

Matches all groups of the haystack string using the pattern regular expression. Returns an array of arrays, where each array includes matching fragments from every group. Fragments are grouped in order of appearance in the haystack.

Syntax

extractAllGroupsVertical(haystack, pattern)

Arguments

• haystack — Input string. Type: String.
• pattern — Regular expression with re2 syntax. Must contain groups, each group enclosed in parentheses. If pattern contains no groups, an exception is thrown. Type: String.

Returned value

• Type: Array.

If haystack does not match the pattern regex, an empty array is returned.

Example

SELECT extractAllGroupsVertical('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)');

Result:

┌─extractAllGroupsVertical('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)')─┐
│ [['abc','111'],['def','222'],['ghi','333']]                                            │
└────────────────────────────────────────────────────────────────────────────────────────┘

like

Returns whether string haystack matches the LIKE expression pattern.

A LIKE expression can contain normal characters and the following metasymbols:

• % indicates an arbitrary number of arbitrary characters (including zero characters).
• _ indicates a single arbitrary character.
• \ is for escaping literals %, _ and \.

Matching is based on UTF-8, e.g. _ matches the Unicode code point ¥ which is represented in UTF-8 using two bytes.

If the haystack or the LIKE expression are not valid UTF-8, the behavior is undefined.

No automatic Unicode normalization is performed, you can use the normalizeUTF8*() functions for that.

To match against literal %, _ and \ (which are LIKE metacharacters), prepend them with a backslash: \%, \_ and \\. The backslash loses its special meaning (i.e. is interpreted literally) if it prepends a character different than %, _ or \. Note that ClickHouse requires backslashes in strings to be quoted as well, so you would actually need to write \\%, \\_ and \\\\.

For LIKE expressions of the form %needle%, the function is as fast as the position function. All other LIKE expressions are internally converted to a regular expression and executed with a performance similar to function match.

Syntax

like(haystack, pattern)

Alias: haystack LIKE pattern (operator)

notLike

Like like but negates the result.

Alias: haystack NOT LIKE pattern (operator)

ilike

Like like but searches case-insensitively.

Alias: haystack ILIKE pattern (operator)

notILike

Like ilike but negates the result.

Alias: haystack NOT ILIKE pattern (operator)

ngramDistance

Calculates the 4-gram distance between a haystack string and a needle string. For this, it counts the symmetric difference between two multisets of 4-grams and normalizes it by the sum of their cardinalities. Returns a Float32 between 0 and 1. The smaller the result is, the more similar the strings are to each other.

Functions ngramDistanceCaseInsensitive, ngramDistanceUTF8, ngramDistanceCaseInsensitiveUTF8 provide case-insensitive and/or UTF-8 variants of this function.

Syntax

ngramDistance(haystack, needle)

Parameters

• haystack: First comparison string. String literal
• needle: Second comparison string. String literal

Returned value

• Value between 0 and 1 representing the similarity between the two strings. Float32

Implementation details

This function will throw an exception if constant needle or haystack arguments are more than 32Kb in size. If any non-constant haystack or needle arguments are more than 32Kb in size, then the distance is always 1.

Examples

The more similar two strings are to each other, the closer the result will be to 0 (identical).

Query:

SELECT ngramDistance('ClickHouse','ClickHouse!');

Result:

0.06666667

The less similar two strings are to each, the larger the result will be.

Query:

SELECT ngramDistance('ClickHouse','House');

Result:

0.5555556

ngramDistanceCaseInsensitive

Provides a case-insensitive variant of ngramDistance.

Syntax

ngramDistanceCaseInsensitive(haystack, needle)

Parameters

• haystack: First comparison string. String literal
• needle: Second comparison string. String literal

Returned value

• Value between 0 and 1 representing the similarity between the two strings. Float32

Examples

With ngramDistance differences in case will affect the similarity value:

Query:

SELECT ngramDistance('ClickHouse','clickhouse');

Result:

0.71428573

With ngramDistanceCaseInsensitive case is ignored so two identical strings differing only in case will now return a low similarity value:

Query:

SELECT ngramDistanceCaseInsensitive('ClickHouse','clickhouse');

Result:

0

ngramDistanceUTF8

Provides a UTF-8 variant of ngramDistance. Assumes that needle and haystack strings are UTF-8 encoded strings.

Syntax

ngramDistanceUTF8(haystack, needle)

Parameters

• haystack: First UTF-8 encoded comparison string. String literal
• needle: Second UTF-8 encoded comparison string. String literal

Returned value

• Value between 0 and 1 representing the similarity between the two strings. Float32

Example

Query:

SELECT ngramDistanceUTF8('abcde','cde');

Result:

0.5

ngramDistanceCaseInsensitiveUTF8

Provides a case-insensitive variant of ngramDistanceUTF8.

Syntax

ngramDistanceCaseInsensitiveUTF8(haystack, needle)

Parameters

• haystack: First UTF-8 encoded comparison string. String literal
• needle: Second UTF-8 encoded comparison string. String literal

Returned value

• Value between 0 and 1 representing the similarity between the two strings. Float32

Example

Query:

SELECT ngramDistanceCaseInsensitiveUTF8('abcde','CDE');

Result:

0.5

ngramSearch

Like ngramDistance but calculates the non-symmetric difference between a needle string and a haystack string, i.e. the number of n-grams from the needle minus the common number of n-grams normalized by the number of needle n-grams. Returns a Float32 between 0 and 1. The bigger the result is, the more likely needle is in the haystack. This function is useful for fuzzy string search. Also see function soundex.

Functions ngramSearchCaseInsensitive, ngramSearchUTF8, ngramSearchCaseInsensitiveUTF8 provide case-insensitive and/or UTF-8 variants of this function.

Syntax

ngramSearch(haystack, needle)

Parameters

• haystack: First comparison string. String literal
• needle: Second comparison string. String literal

Returned value

• Value between 0 and 1 representing the likelihood of the needle being in the haystack. Float32

Implementation details

:::note The UTF-8 variants use the 3-gram distance. These are not perfectly fair n-gram distances. We use 2-byte hashes to hash n-grams and then calculate the (non-)symmetric difference between these hash tables – collisions may occur. With UTF-8 case-insensitive format we do not use fair tolower function – we zero the 5-th bit (starting from zero) of each codepoint byte and first bit of zeroth byte if bytes more than one – this works for Latin and mostly for all Cyrillic letters. :::

Example

Query:

SELECT ngramSearch('Hello World','World Hello');

Result:

0.5

ngramSearchCaseInsensitive

Provides a case-insensitive variant of ngramSearch.

Syntax

ngramSearchCaseInsensitive(haystack, needle)

Parameters

• haystack: First comparison string. String literal
• needle: Second comparison string. String literal

Returned value

• Value between 0 and 1 representing the likelihood of the needle being in the haystack. Float32

The bigger the result is, the more likely needle is in the haystack.

Example

Query:

SELECT ngramSearchCaseInsensitive('Hello World','hello');

Result:

1

ngramSearchUTF8

Provides a UTF-8 variant of ngramSearch in which needle and haystack are assumed to be UTF-8 encoded strings.

Syntax

ngramSearchUTF8(haystack, needle)

Parameters

• haystack: First UTF-8 encoded comparison string. String literal
• needle: Second UTF-8 encoded comparison string. String literal

Returned value

• Value between 0 and 1 representing the likelihood of the needle being in the haystack. Float32

The bigger the result is, the more likely needle is in the haystack.

Example

Query:

SELECT ngramSearchUTF8('абвгдеёжз', 'гдеёзд');

Result:

0.5

ngramSearchCaseInsensitiveUTF8

Provides a case-insensitive variant of ngramSearchUTF8 in which needle and haystack.

Syntax

ngramSearchCaseInsensitiveUTF8(haystack, needle)

Parameters

• haystack: First UTF-8 encoded comparison string. String literal
• needle: Second UTF-8 encoded comparison string. String literal

Returned value

• Value between 0 and 1 representing the likelihood of the needle being in the haystack. Float32

The bigger the result is, the more likely needle is in the haystack.

Example

Query:

SELECT ngramSearchCaseInsensitiveUTF8('абвГДЕёжз', 'АбвгдЕЁжз');

Result:

0.57142854

countSubstrings

Returns how often substring needle occurs in string haystack.

Functions countSubstringsCaseInsensitive and countSubstringsCaseInsensitiveUTF8 provide a case-insensitive and case-insensitive + UTF-8 variants of this function.

Syntax

countSubstrings(haystack, needle[, start_pos])

Arguments

• haystack — String in which the search is performed. String.
• needle — Substring to be searched. String.
• start_pos – Position (1-based) in haystack at which the search starts. UInt. Optional.

Returned values

• The number of occurrences.

Type: UInt64.

Examples

SELECT countSubstrings('aaaa', 'aa');

Result:

┌─countSubstrings('aaaa', 'aa')─┐
│                             2 │
└───────────────────────────────┘

Example with start_pos argument:

SELECT countSubstrings('abc___abc', 'abc', 4);

Result:

┌─countSubstrings('abc___abc', 'abc', 4)─┐
│                                      1 │
└────────────────────────────────────────┘

countMatches

Returns the number of regular expression matches for a pattern in a haystack.

Syntax

countMatches(haystack, pattern)

Arguments

• haystack — The string to search in. String.
• pattern — The regular expression with re2 syntax. String.

Returned value

• The number of matches.

Type: UInt64.

Examples

SELECT countMatches('foobar.com', 'o+');

Result:

┌─countMatches('foobar.com', 'o+')─┐
│                                2 │
└──────────────────────────────────┘

SELECT countMatches('aaaa', 'aa');

Result:

┌─countMatches('aaaa', 'aa')────┐
│                             2 │
└───────────────────────────────┘

countMatchesCaseInsensitive

Like countMatches(haystack, pattern) but matching ignores the case.

regexpExtract

Extracts the first string in haystack that matches the regexp pattern and corresponds to the regex group index.

Syntax

regexpExtract(haystack, pattern[, index])

Alias: REGEXP_EXTRACT(haystack, pattern[, index]).

Arguments

• haystack — String, in which regexp pattern will to be matched. String.
• pattern — String, regexp expression, must be constant. String.
• index – An integer number greater or equal 0 with default 1. It represents which regex group to extract. UInt or Int. Optional.

Returned values

pattern may contain multiple regexp groups, index indicates which regex group to extract. An index of 0 means matching the entire regular expression.

Type: String.

Examples

SELECT
    regexpExtract('100-200', '(\\d+)-(\\d+)', 1),
    regexpExtract('100-200', '(\\d+)-(\\d+)', 2),
    regexpExtract('100-200', '(\\d+)-(\\d+)', 0),
    regexpExtract('100-200', '(\\d+)-(\\d+)');

Result:

┌─regexpExtract('100-200', '(\\d+)-(\\d+)', 1)─┬─regexpExtract('100-200', '(\\d+)-(\\d+)', 2)─┬─regexpExtract('100-200', '(\\d+)-(\\d+)', 0)─┬─regexpExtract('100-200', '(\\d+)-(\\d+)')─┐
│ 100                                          │ 200                                          │ 100-200                                      │ 100                                       │
└──────────────────────────────────────────────┴──────────────────────────────────────────────┴──────────────────────────────────────────────┴───────────────────────────────────────────┘

hasSubsequence

Returns 1 if needle is a subsequence of haystack, or 0 otherwise. A subsequence of a string is a sequence that can be derived from the given string by deleting zero or more elements without changing the order of the remaining elements.

Syntax

hasSubsequence(haystack, needle)

Arguments

• haystack — String in which the search is performed. String.
• needle — Subsequence to be searched. String.

Returned values

• 1, if needle is a subsequence of haystack.
• 0, otherwise.

Type: UInt8.

Examples

Query:

SELECT hasSubsequence('garbage', 'arg');

Result:

┌─hasSubsequence('garbage', 'arg')─┐
│                                1 │
└──────────────────────────────────┘

hasSubsequenceCaseInsensitive

Like hasSubsequence but searches case-insensitively.

Syntax

hasSubsequenceCaseInsensitive(haystack, needle)

Arguments

• haystack — String in which the search is performed. String.
• needle — Subsequence to be searched. String.

Returned values

• 1, if needle is a subsequence of haystack.
• 0, otherwise.

Type: UInt8.

Examples

Query:

SELECT hasSubsequenceCaseInsensitive('garbage', 'ARG');

Result:

┌─hasSubsequenceCaseInsensitive('garbage', 'ARG')─┐
│                                               1 │
└─────────────────────────────────────────────────┘

hasSubsequenceUTF8

Like hasSubsequence but assumes haystack and needle are UTF-8 encoded strings.

Syntax

hasSubsequenceUTF8(haystack, needle)

Arguments

• haystack — String in which the search is performed. UTF-8 encoded String.
• needle — Subsequence to be searched. UTF-8 encoded String.

Returned values

• 1, if needle is a subsequence of haystack.
• 0, otherwise.

Type: UInt8.

Query:

Examples

select hasSubsequenceUTF8('ClickHouse - столбцовая система управления базами данных', 'система');

Result:

┌─hasSubsequenceUTF8('ClickHouse - столбцовая система управления базами данных', 'система')─┐
│                                                                                         1 │
└───────────────────────────────────────────────────────────────────────────────────────────┘

hasSubsequenceCaseInsensitiveUTF8

Like hasSubsequenceUTF8 but searches case-insensitively.

Syntax

hasSubsequenceCaseInsensitiveUTF8(haystack, needle)

Arguments

• haystack — String in which the search is performed. UTF-8 encoded String.
• needle — Subsequence to be searched. UTF-8 encoded String.

Returned values

• 1, if needle is a subsequence of haystack.
• 0, otherwise.

Type: UInt8.

Examples

Query:

select hasSubsequenceCaseInsensitiveUTF8('ClickHouse - столбцовая система управления базами данных', 'СИСТЕМА');

Result:

┌─hasSubsequenceCaseInsensitiveUTF8('ClickHouse - столбцовая система управления базами данных', 'СИСТЕМА')─┐
│                                                                                                        1 │
└──────────────────────────────────────────────────────────────────────────────────────────────────────────┘

hasToken

Returns 1 if a given token is present in a haystack, or 0 otherwise.

Syntax

hasToken(haystack, token)

Parameters

• haystack: String in which the search is performed. String.
• token: Maximal length substring between two non alphanumeric ASCII characters (or boundaries of haystack).

Returned value

• 1, if the token is present in the haystack.
• 0, if the token is not present.

Implementation details

Token must be a constant string. Supported by tokenbf_v1 index specialization.

Example

Query:

SELECT hasToken('Hello World','Hello');

1

hasTokenOrNull

Returns 1 if a given token is present, 0 if not present, and null if the token is ill-formed.

Syntax

hasTokenOrNull(haystack, token)

Parameters

• haystack: String in which the search is performed. String.
• token: Maximal length substring between two non alphanumeric ASCII characters (or boundaries of haystack).

Returned value

• 1, if the token is present in the haystack.
• 0, if the token is not present in the haystack.
• null, if the token is ill-formed.

Implementation details

Token must be a constant string. Supported by tokenbf_v1 index specialization.

Example

Where hasToken would throw an error for an ill-formed token, hasTokenOrNull returns null for an ill-formed token.

Query:

SELECT hasTokenOrNull('Hello World','Hello,World');

null

hasTokenCaseInsensitive

Returns 1 if a given token is present in a haystack, 0 otherwise. Ignores case.

Syntax

hasTokenCaseInsensitive(haystack, token)

Parameters

• haystack: String in which the search is performed. String.
• token: Maximal length substring between two non alphanumeric ASCII characters (or boundaries of haystack).

Returned value

• 1, if the token is present in the haystack.
• 0, otherwise.

Implementation details

Token must be a constant string. Supported by tokenbf_v1 index specialization.

Example

Query:

SELECT hasTokenCaseInsensitive('Hello World','hello');

1

hasTokenCaseInsensitiveOrNull

Returns 1 if a given token is present in a haystack, 0 otherwise. Ignores case and returns null if the token is ill-formed.

Syntax

hasTokenCaseInsensitiveOrNull(haystack, token)

Parameters

• haystack: String in which the search is performed. String.
• token: Maximal length substring between two non alphanumeric ASCII characters (or boundaries of haystack).

Returned value

• 1, if the token is present in the haystack.
• 0, if token is not present.
• null, if the token is ill-formed.

Implementation details

Token must be a constant string. Supported by tokenbf_v1 index specialization.

Example

Where hasTokenCaseInsensitive would throw an error for an ill-formed token, hasTokenCaseInsensitiveOrNull returns null for an ill-formed token.

Query:

SELECT hasTokenCaseInsensitiveOrNull('Hello World','hello,world');

null