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

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/en/sql-reference/functions/string-search-functions	41	Searching in Strings

Functions for Searching in Strings

The search is case-sensitive by default in all these functions. There are separate variants for case insensitive search.

:::note Functions for replacing and other manipulations with strings are described separately. :::

position(haystack, needle), locate(haystack, needle)

Searches for the substring needle in the string haystack.

Returns the position (in bytes) of the found substring in the string, starting from 1.

For a case-insensitive search, use the function positionCaseInsensitive.

Syntax

position(haystack, needle[, start_pos])

position(needle IN haystack)

Alias: locate(haystack, needle[, start_pos]).

:::note Syntax of position(needle IN haystack) provides SQL-compatibility, the function works the same way as to position(haystack, needle). :::

Arguments

• haystack — String, in which substring will to be searched. String.
• needle — Substring to be searched. String.
• start_pos – Position of the first character in the string to start search. UInt. Optional.

Returned values

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

Type: Integer.

Examples

The phrase “Hello, world!” contains a set of bytes representing a single-byte encoded text. The function returns some expected result:

Query:

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

Result:

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

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

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

The same phrase in Russian contains characters which can’t be represented using a single byte. The function returns some unexpected result (use positionUTF8 function for multi-byte encoded text):

Query:

SELECT position('Привет, мир!', '!');

Result:

┌─position('Привет, мир!', '!')─┐
│                            21 │
└───────────────────────────────┘

If argument needle is empty the following 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 positionCaseInsensitive, positionUTF8 and positionCaseInsensitiveUTF8

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

┌─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 │
└─────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┘

Examples for POSITION(needle IN haystack) syntax

Query:

SELECT 3 = position('c' IN 'abc');

Result:

┌─equals(3, position('abc', 'c'))─┐
│                               1 │
└─────────────────────────────────┘

Query:

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

Result:

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

positionCaseInsensitive

The same as position returns the position (in bytes) of the found substring in the string, starting from 1. Use the function for a case-insensitive search.

Works under the assumption that the string contains a set of bytes representing a single-byte encoded text. If this assumption is not met and a character can’t be represented using a single byte, the function does not throw an exception and returns some unexpected result. If character can be represented using two bytes, it will use two bytes and so on.

Syntax

positionCaseInsensitive(haystack, needle[, start_pos])

Arguments

• haystack — String, in which substring will to be searched. String.
• needle — Substring to be searched. String.
• start_pos — Optional parameter, position of the first character in the string to start search. UInt.

Returned values

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

Type: Integer.

Example

Query:

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

Result:

┌─positionCaseInsensitive('Hello, world!', 'hello')─┐
│                                                 1 │
└───────────────────────────────────────────────────┘

positionUTF8

Returns the position (in Unicode points) of the found substring in the string, starting from 1.

Works under the assumption that the string contains a set of bytes representing a UTF-8 encoded text. If this assumption is not met, the function does not throw an exception and returns some unexpected result. If character can be represented using two Unicode points, it will use two and so on.

For a case-insensitive search, use the function positionCaseInsensitiveUTF8.

Syntax

positionUTF8(haystack, needle[, start_pos])

Arguments

• haystack — String, in which substring will to be searched. String.
• needle — Substring to be searched. String.
• start_pos — Optional parameter, position of the first character in the string to start search. UInt

Returned values

• Starting position in Unicode points (counting from 1), if substring was found.
• 0, if the substring was not found.

Type: Integer.

Examples

The phrase “Hello, world!” in Russian contains a set of Unicode points representing a single-point encoded text. The function returns some expected result:

Query:

SELECT positionUTF8('Привет, мир!', '!');

Result:

┌─positionUTF8('Привет, мир!', '!')─┐
│                                12 │
└───────────────────────────────────┘

The phrase “Salut, étudiante!”, where character é can be represented using a one point (U+00E9) or two points (U+0065U+0301) the function can be returned some unexpected result:

Query for the letter é, which is represented one Unicode point U+00E9:

SELECT positionUTF8('Salut, étudiante!', '!');

Result:

┌─positionUTF8('Salut, étudiante!', '!')─┐
│                                     17 │
└────────────────────────────────────────┘

Query for the letter é, which is represented two Unicode points U+0065U+0301:

SELECT positionUTF8('Salut, étudiante!', '!');

Result:

┌─positionUTF8('Salut, étudiante!', '!')─┐
│                                     18 │
└────────────────────────────────────────┘

positionCaseInsensitiveUTF8

The same as positionUTF8, but is case-insensitive. Returns the position (in Unicode points) of the found substring in the string, starting from 1.

Works under the assumption that the string contains a set of bytes representing a UTF-8 encoded text. If this assumption is not met, the function does not throw an exception and returns some unexpected result. If character can be represented using two Unicode points, it will use two and so on.

Syntax

positionCaseInsensitiveUTF8(haystack, needle[, start_pos])

Arguments

• haystack — String, in which substring will to be searched. String.
• needle — Substring to be searched. String.
• start_pos — Optional parameter, position of the first character in the string to start search. UInt

Returned value

• Starting position in Unicode points (counting from 1), if substring was found.
• 0, if the substring was not found.

Type: Integer.

Example

Query:

SELECT positionCaseInsensitiveUTF8('Привет, мир!', 'Мир');

Result:

┌─positionCaseInsensitiveUTF8('Привет, мир!', 'Мир')─┐
│                                                  9 │
└────────────────────────────────────────────────────┘

multiSearchAllPositions

The same as position but returns Array of positions (in bytes) of the found corresponding substrings in the string. Positions are indexed starting from 1.

The search is performed on sequences of bytes without respect to string encoding and collation.

• For case-insensitive ASCII search, use the function multiSearchAllPositionsCaseInsensitive.
• For search in UTF-8, use the function multiSearchAllPositionsUTF8.
• For case-insensitive UTF-8 search, use the function multiSearchAllPositionsCaseInsensitiveUTF8.

Syntax

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

Arguments

• haystack — String, in which substring will to be searched. String.
• needle — Substring to be searched. String.

Returned values

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

Example

Query:

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

Result:

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

multiSearchAllPositionsUTF8

See multiSearchAllPositions.

multiSearchFirstPosition(haystack, [needle₁, needle₂, …, needle_n])

The same as position but returns the leftmost offset of the string haystack that is matched to some of the needles.

For a case-insensitive search or/and in UTF-8 format use functions multiSearchFirstPositionCaseInsensitive, multiSearchFirstPositionUTF8, multiSearchFirstPositionCaseInsensitiveUTF8.

multiSearchFirstIndex(haystack, [needle₁, needle₂, …, needle_n])

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

For a case-insensitive search or/and in UTF-8 format use functions multiSearchFirstIndexCaseInsensitive, multiSearchFirstIndexUTF8, multiSearchFirstIndexCaseInsensitiveUTF8.

multiSearchAny(haystack, [needle₁, needle₂, …, needle_n])

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

For a case-insensitive search or/and in UTF-8 format use functions multiSearchAnyCaseInsensitive, multiSearchAnyUTF8, multiSearchAnyCaseInsensitiveUTF8.

:::note In all multiSearch* functions the number of needles should be less than 2⁸ because of implementation specification. :::

match(haystack, pattern)

Checks whether string haystack matches the regular expression pattern. The pattern is an re2 regular expression which has a more limited syntax than Perl regular expressions.

Returns 1 in case of a match, and 0 otherwise.

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

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

For patterns to search for substrings in a string, it is better to use functions like or position since they work much faster.

multiMatchAny(haystack, [pattern₁, pattern₂, …, pattern_n])

The same as match, but returns 0 if none of the regular expressions are matched and 1 if any of the patterns matches. For patterns to search substrings in a string, it is better to use multiSearchAny since it works much faster.

:::note Functions multiMatchAny, multiMatchAnyIndex, multiMatchAllIndices and their fuzzy equivalents (multiFuzzyMatchAny, multiFuzzyMatchAnyIndex, multiFuzzyMatchAllIndices) use the (Vectorscan)[https://github.com/VectorCamp/vectorscan] library. As such, they are only enabled if ClickHouse is compiled with support for vectorscan.

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. :::

multiMatchAnyIndex(haystack, [pattern₁, pattern₂, …, pattern_n])

The same as multiMatchAny, but returns any index that matches the haystack.

multiMatchAllIndices(haystack, [pattern₁, pattern₂, …, pattern_n])

The same as multiMatchAny, but returns the array of all indices that match the haystack in any order.

multiFuzzyMatchAny(haystack, distance, [pattern₁, pattern₂, …, pattern_n])

The same as 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.

multiFuzzyMatchAnyIndex(haystack, distance, [pattern₁, pattern₂, …, pattern_n])

The same as multiFuzzyMatchAny, but returns any index that matches the haystack within a constant edit distance.

multiFuzzyMatchAllIndices(haystack, distance, [pattern₁, pattern₂, …, pattern_n])

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

:::note multiFuzzyMatch* functions do not support UTF-8 regular expressions, and such expressions are treated as bytes because of hyperscan restriction. :::

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

extract(haystack, pattern)

Extracts a fragment of a string using a regular expression. If ‘haystack’ does not match the ‘pattern’ regex, an empty string is returned. If the regex does not contain subpatterns, it takes the fragment that matches the entire regex. Otherwise, it takes the fragment that matches the first subpattern.

extractAll(haystack, pattern)

Extracts all the 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 to the regex. In general, the behavior is the same as the ‘extract’ function (it takes the first subpattern, or the entire expression if there isn’t a subpattern).

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.

:::note extractAllGroupsHorizontal 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

Query:

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']]                                                │
└──────────────────────────────────────────────────────────────────────────────────────────┘

See Also

• extractAllGroupsVertical

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

Query:

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']]                                            │
└────────────────────────────────────────────────────────────────────────────────────────┘

See Also

• extractAllGroupsHorizontal

like(haystack, pattern), haystack LIKE pattern operator

Checks whether a string matches a LIKE expression. A LIKE expression contains a mix of 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 pattern are not valid UTF-8, then the behavior is undefined. No automatic Unicode normalization is performed, you can use the normalizeUTF8*() functions for that.

To match against literals %, _ and / (which are LIKE metacharacters), prepend them with a backslash, i.e. \%, \_ 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 patterns of the form %needle%, the function is as fast as the position function. Other LIKE expressions are internally converted to a regular expression and executed with a performance similar to function match.

notLike(haystack, pattern), haystack NOT LIKE pattern operator

The same thing as ‘like’, but negative.

ilike

Case insensitive variant of like function. You can use ILIKE operator instead of the ilike function.

The function ignores the language, e.g. for Turkish (i/İ), the result might be incorrect.

Syntax

ilike(haystack, pattern)

Arguments

• haystack — Input string. String.
• pattern — If pattern does not contain percent signs or underscores, then the pattern only represents the string itself. An underscore (_) in pattern stands for (matches) any single character. A percent sign (%) matches any sequence of zero or more characters.

Some pattern examples:

'abc' ILIKE 'abc'    true
'abc' ILIKE 'a%'     true
'abc' ILIKE '_b_'    true
'abc' ILIKE 'c'      false

Returned values

• True, if the string matches pattern.
• False, if the string does not match pattern.

Example

Input table:

┌─id─┬─name─────┬─days─┐
│  1 │ January  │   31 │
│  2 │ February │   29 │
│  3 │ March    │   31 │
│  4 │ April    │   30 │
└────┴──────────┴──────┘

Query:

SELECT * FROM Months WHERE ilike(name, '%j%');

Result:

┌─id─┬─name────┬─days─┐
│  1 │ January │   31 │
└────┴─────────┴──────┘

notILike(haystack, pattern), haystack NOT ILIKE pattern operator

The same thing as ‘ilike’, but negative.

ngramDistance(haystack, needle)

Calculates the 4-gram distance between haystack and needle: counts the symmetric difference between two multisets of 4-grams and normalizes it by the sum of their cardinalities. Returns float number from 0 to 1 – the closer to zero, the more strings are similar to each other. If the constant needle or haystack is more than 32Kb, throws an exception. If some of the non-constant haystack or needle strings are more than 32Kb, the distance is always one.

For case-insensitive search or/and in UTF-8 format use functions ngramDistanceCaseInsensitive, ngramDistanceUTF8, ngramDistanceCaseInsensitiveUTF8.

ngramSearch(haystack, needle)

Same as ngramDistance but calculates the non-symmetric difference between needle and haystack – the number of n-grams from needle minus the common number of n-grams normalized by the number of needle n-grams. The closer to one, the more likely needle is in the haystack. Can be useful for fuzzy string search.

For case-insensitive search or/and in UTF-8 format use functions ngramSearchCaseInsensitive, ngramSearchUTF8, ngramSearchCaseInsensitiveUTF8.

:::note For UTF-8 case we use 3-gram distance. All 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. :::

countSubstrings

Returns the number of substring occurrences.

For a case-insensitive search, use countSubstringsCaseInsensitive or countSubstringsCaseInsensitiveUTF8 functions.

Syntax

countSubstrings(haystack, needle[, start_pos])

Arguments

• haystack — The string to search in. String.
• needle — The substring to search for. String.
• start_pos – Position of the first character in the string to start search. Optional. UInt.

Returned values

• Number of occurrences.

Type: UInt64.

Examples

Query:

SELECT countSubstrings('foobar.com', '.');

Result:

┌─countSubstrings('foobar.com', '.')─┐
│                                  1 │
└────────────────────────────────────┘

Query:

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

Result:

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

Query:

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

Result:

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

countSubstringsCaseInsensitive

Returns the number of substring occurrences case-insensitive.

Syntax

countSubstringsCaseInsensitive(haystack, needle[, start_pos])

Arguments

• haystack — The string to search in. String.
• needle — The substring to search for. String.
• start_pos — Position of the first character in the string to start search. Optional. UInt.

Returned values

• Number of occurrences.

Type: UInt64.

Examples

Query:

SELECT countSubstringsCaseInsensitive('aba', 'B');

Result:

┌─countSubstringsCaseInsensitive('aba', 'B')─┐
│                                          1 │
└────────────────────────────────────────────┘

Query:

SELECT countSubstringsCaseInsensitive('foobar.com', 'CoM');

Result:

┌─countSubstringsCaseInsensitive('foobar.com', 'CoM')─┐
│                                                   1 │
└─────────────────────────────────────────────────────┘

Query:

SELECT countSubstringsCaseInsensitive('abC___abC', 'aBc', 2);

Result:

┌─countSubstringsCaseInsensitive('abC___abC', 'aBc', 2)─┐
│                                                     1 │
└───────────────────────────────────────────────────────┘

countSubstringsCaseInsensitiveUTF8

Returns the number of substring occurrences in UTF-8 case-insensitive.

Syntax

SELECT countSubstringsCaseInsensitiveUTF8(haystack, needle[, start_pos])

Arguments

• haystack — The string to search in. String.
• needle — The substring to search for. String.
• start_pos — Position of the first character in the string to start search. Optional. UInt.

Returned values

• Number of occurrences.

Type: UInt64.

Examples

Query:

SELECT countSubstringsCaseInsensitiveUTF8('абв', 'A');

Result:

┌─countSubstringsCaseInsensitiveUTF8('абв', 'A')─┐
│                                              1 │
└────────────────────────────────────────────────┘

Query:

SELECT countSubstringsCaseInsensitiveUTF8('аБв__АбВ__абв', 'Абв');

Result:

┌─countSubstringsCaseInsensitiveUTF8('аБв__АбВ__абв', 'Абв')─┐
│                                                          3 │
└────────────────────────────────────────────────────────────┘

countMatches(haystack, pattern)

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

Query:

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

Result:

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

Query:

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

Result:

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

regexpExtract(haystack, pattern[, index])

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+)')

┌─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                                       │
└──────────────────────────────────────────────┴──────────────────────────────────────────────┴──────────────────────────────────────────────┴───────────────────────────────────────────┘