diff --git a/docs/en/sql-reference/functions/string-functions.md b/docs/en/sql-reference/functions/string-functions.md index 555234089e6..37135811cd7 100644 --- a/docs/en/sql-reference/functions/string-functions.md +++ b/docs/en/sql-reference/functions/string-functions.md @@ -6,9 +6,7 @@ sidebar_label: Strings # Functions for Working with Strings -:::note Functions for [searching](../../sql-reference/functions/string-search-functions.md) in strings and for [replacing](../../sql-reference/functions/string-replace-functions.md) in strings are described separately. -::: ## empty diff --git a/docs/en/sql-reference/functions/string-replace-functions.md b/docs/en/sql-reference/functions/string-replace-functions.md index 084b20bb3eb..f80e435c82f 100644 --- a/docs/en/sql-reference/functions/string-replace-functions.md +++ b/docs/en/sql-reference/functions/string-replace-functions.md @@ -6,9 +6,7 @@ sidebar_label: Replacing in Strings # Functions for Searching and Replacing in Strings -:::note Functions for [searching](../../sql-reference/functions/string-search-functions.md) and [other manipulations with strings](../../sql-reference/functions/string-functions.md) are described separately. -::: ## replaceOne(haystack, pattern, replacement) diff --git a/docs/en/sql-reference/functions/string-search-functions.md b/docs/en/sql-reference/functions/string-search-functions.md index 587636376f9..49296dc7239 100644 --- a/docs/en/sql-reference/functions/string-search-functions.md +++ b/docs/en/sql-reference/functions/string-search-functions.md @@ -6,19 +6,22 @@ sidebar_label: 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. +All functions in this section search by default case-sensitively. Case-insensitive search is usually provided by separate function variants. +Note that case-insensitive search follows the lowercase-uppercase rules of the English language. E.g. Uppercased `i` in English language is +`I` whereas in Turkish language it is `İ` - results for languages other than English may be unexpected. -:::note -Functions for [replacing](../../sql-reference/functions/string-replace-functions.md) and [other manipulations with strings](../../sql-reference/functions/string-functions.md) are described separately. -::: +Functions in this section also assume that the searched string and the search string 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, you can use the +[normalizeUTF8*()](https://clickhouse.com/docs/en/sql-reference/functions/string-functions/) functions for that. -## position(haystack, needle), locate(haystack, needle) -Searches for the substring `needle` in the string `haystack`. +[General strings functions](../../sql-reference/functions/string-functions.md) and [functions for replacing in strings](../../sql-reference/functions/string-replace-functions.md) are described separately. -Returns the position (in bytes) of the found substring in the string, starting from 1. +## position -For a case-insensitive search, use the function [positionCaseInsensitive](#positioncaseinsensitive). +Returns the position (in bytes, starting at 1) of a substring `needle` in a string `haystack`. **Syntax** @@ -26,35 +29,33 @@ For a case-insensitive search, use the function [positionCaseInsensitive](#posit position(haystack, needle[, start_pos]) ``` -``` sql -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)`. -::: +Alias: +- `position(needle IN haystack)` +- `locate(haystack, needle[, start_pos])`. **Arguments** -- `haystack` — String, in which substring will to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). +- `haystack` — String in which the search is performed. [String](../../sql-reference/syntax.md#syntax-string-literal). - `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` – Position of the first character in the string to start search. [UInt](../../sql-reference/data-types/int-uint.md). Optional. +- `start_pos` – Position (1-based) in `haystack` at which the search starts. [UInt](../../sql-reference/data-types/int-uint.md). Optional. **Returned values** -- Starting position in bytes (counting from 1), if substring was found. +- 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 `positionCaseInsensitive`, `positionUTF8` and `positionCaseInsensitiveUTF8` + 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: - ``` sql SELECT position('Hello, world!', '!'); ``` @@ -67,6 +68,8 @@ Result: └────────────────────────────────┘ ``` +Example with `start_pos` argument: + ``` sql SELECT position('Hello, world!', 'o', 1), @@ -79,29 +82,21 @@ SELECT └───────────────────────────────────┴───────────────────────────────────┘ ``` -The same phrase in Russian contains characters which can’t be represented using a single byte. The function returns some unexpected result (use [positionUTF8](#positionutf8) function for multi-byte encoded text): +Example for `needle IN haystack` syntax: -Query: - -``` sql -SELECT position('Привет, мир!', '!'); +```sql +SELECT 6 = position('/' IN s) FROM (SELECT 'Hello/World' AS s); ``` Result: -``` text -┌─position('Привет, мир!', '!')─┐ -│ 21 │ -└───────────────────────────────┘ +```text +┌─equals(6, position(s, '/'))─┐ +│ 1 │ +└─────────────────────────────┘ ``` -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` +Examples with empty `needle` substring: ``` sql SELECT @@ -120,223 +115,59 @@ SELECT └─────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┴────────────────────────┘ ``` - -**Examples for POSITION(needle IN haystack) syntax** - -Query: - -```sql -SELECT 3 = position('c' IN 'abc'); -``` - -Result: - -```text -┌─equals(3, position('abc', 'c'))─┐ -│ 1 │ -└─────────────────────────────────┘ -``` - -Query: - -```sql -SELECT 6 = position('/' IN s) FROM (SELECT 'Hello/World' AS s); -``` - -Result: - -```text -┌─equals(6, position(s, '/'))─┐ -│ 1 │ -└─────────────────────────────┘ -``` - ## positionCaseInsensitive -The same as [position](#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** - -``` sql -positionCaseInsensitive(haystack, needle[, start_pos]) -``` - -**Arguments** - -- `haystack` — String, in which substring will to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` — Optional parameter, position of the first character in the string to start search. [UInt](../../sql-reference/data-types/int-uint.md). - -**Returned values** - -- Starting position in bytes (counting from 1), if substring was found. -- 0, if the substring was not found. - -Type: `Integer`. - -**Example** - -Query: - -``` sql -SELECT positionCaseInsensitive('Hello, world!', 'hello'); -``` - -Result: - -``` text -┌─positionCaseInsensitive('Hello, world!', 'hello')─┐ -│ 1 │ -└───────────────────────────────────────────────────┘ -``` +Like [position](#position) but searches case-insensitively. ## 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](#positioncaseinsensitiveutf8). - -**Syntax** - -``` sql -positionUTF8(haystack, needle[, start_pos]) -``` - -**Arguments** - -- `haystack` — String, in which substring will to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` — Optional parameter, position of the first character in the string to start search. [UInt](../../sql-reference/data-types/int-uint.md) - -**Returned values** - -- Starting position in Unicode points (counting from 1), if substring was found. -- 0, if the substring was not found. - -Type: `Integer`. +Like [position](#position) but assumes `haystack` and `needle` are UTF-8 encoded strings. **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: +Function `positionUTF8` correctly counts character `ö` (represented by two points) as a single Unicode codepoint: ``` sql -SELECT positionUTF8('Привет, мир!', '!'); +SELECT positionUTF8('Motörhead', 'r'); ``` Result: ``` text -┌─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`: - -``` sql -SELECT positionUTF8('Salut, étudiante!', '!'); -``` - -Result: - -``` text -┌─positionUTF8('Salut, étudiante!', '!')─┐ -│ 17 │ -└────────────────────────────────────────┘ -``` - -Query for the letter `é`, which is represented two Unicode points `U+0065U+0301`: - -``` sql -SELECT positionUTF8('Salut, étudiante!', '!'); -``` - -Result: - -``` text -┌─positionUTF8('Salut, étudiante!', '!')─┐ -│ 18 │ -└────────────────────────────────────────┘ +┌─position('Motörhead', 'r')─┐ +│ 5 │ +└────────────────────────────┘ ``` ## positionCaseInsensitiveUTF8 -The same as [positionUTF8](#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** - -``` sql -positionCaseInsensitiveUTF8(haystack, needle[, start_pos]) -``` - -**Arguments** - -- `haystack` — String, in which substring will to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` — Optional parameter, position of the first character in the string to start search. [UInt](../../sql-reference/data-types/int-uint.md) - -**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: - -``` sql -SELECT positionCaseInsensitiveUTF8('Привет, мир!', 'Мир'); -``` - -Result: - -``` text -┌─positionCaseInsensitiveUTF8('Привет, мир!', 'Мир')─┐ -│ 9 │ -└────────────────────────────────────────────────────┘ -``` +Like [positionUTF8](#positionutf8) but searches case-insensitively. ## multiSearchAllPositions -The same as [position](../../sql-reference/functions/string-search-functions.md#position) but returns `Array` of positions (in bytes) of the found corresponding substrings in the string. Positions are indexed starting from 1. +Like [position](#position) but returns an array of positions (in bytes, starting at 1) for multiple `needle` substrings in a `haystack` string. -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](#multiSearchAllPositionsUTF8). -- For case-insensitive UTF-8 search, use the function multiSearchAllPositionsCaseInsensitiveUTF8. +:::note +All `multiSearch*()` functions only support up to 28 needles. +::: **Syntax** ``` sql -multiSearchAllPositions(haystack, [needle1, needle2, ..., needlen]) +multiSearchAllPositions(haystack, [needle1, needle2, ..., needleN]) ``` **Arguments** -- `haystack` — String, in which substring will to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). +- `haystack` — String in which the search is performed. [String](../../sql-reference/syntax.md#syntax-string-literal). +- `needle` — Substrings to be searched. Array **Returned values** -- Array of starting positions in bytes (counting from 1), if the corresponding substring was found and 0 if not found. +- Array of the starting position in bytes and counting from 1 (if the substring was found) or 0 (if the substring was not found) **Example** -Query: - ``` sql SELECT multiSearchAllPositions('Hello, World!', ['hello', '!', 'world']); ``` @@ -351,103 +182,172 @@ Result: ## multiSearchAllPositionsUTF8 -See `multiSearchAllPositions`. +Like [multiSearchAllPositions](#multiSearchAllPositions) but assumes `haystack` and the `needle`-s are UTF-8 encoded strings. -## multiSearchFirstPosition(haystack, \[needle1, needle2, …, needlen\]) +## multiSearchFirstPosition -The same as `position` but returns the leftmost offset of the string `haystack` that is matched to some of the needles. +Like `position` but returns the leftmost offset in a `haystack` string which matches any of multiple `needle` strings. -For a case-insensitive search or/and in UTF-8 format use functions `multiSearchFirstPositionCaseInsensitive, multiSearchFirstPositionUTF8, multiSearchFirstPositionCaseInsensitiveUTF8`. +Functions `multiSearchFirstPositionCaseInsensitive`, `multiSearchFirstPositionUTF8` and `multiSearchFirstPositionCaseInsensitiveUTF8` provide case-insensitive and/or UTF-8 variants of this function. -## multiSearchFirstIndex(haystack, \[needle1, needle2, …, needlen\]) +**Syntax** + +```sql +multiSearchFirstPosition(haystack, \[needle1, needle2, …, needlen\]) +``` + +## multiSearchFirstIndex Returns the index `i` (starting from 1) of the leftmost found needlei in the string `haystack` and 0 otherwise. -For a case-insensitive search or/and in UTF-8 format use functions `multiSearchFirstIndexCaseInsensitive, multiSearchFirstIndexUTF8, multiSearchFirstIndexCaseInsensitiveUTF8`. +Functions `multiSearchFirstIndexCaseInsensitive`, `multiSearchFirstIndexUTF8` and `multiSearchFirstIndexCaseInsensitiveUTF8` provide case-insensitive and/or UTF-8 variants of this function. -## multiSearchAny(haystack, \[needle1, needle2, …, needlen\]) +**Syntax** + +```sql +multiSearchFirstIndex(haystack, \[needle1, needle2, …, needlen\]) +``` + +## multiSearchAny Returns 1, if at least one string needlei matches the string `haystack` and 0 otherwise. -For a case-insensitive search or/and in UTF-8 format use functions `multiSearchAnyCaseInsensitive, multiSearchAnyUTF8, multiSearchAnyCaseInsensitiveUTF8`. +Functions `multiSearchAnyCaseInsensitive`, `multiSearchAnyUTF8` and `multiSearchAnyCaseInsensitiveUTF8` provide case-insensitive and/or UTF-8 variants of this function. -:::note -In all `multiSearch*` functions the number of needles should be less than 28 because of implementation specification. -::: +**Syntax** -## match(haystack, pattern), haystack REGEXP pattern operator +```sql +multiSearchAny(haystack, \[needle1, needle2, …, needlen\]) +``` -Checks whether string `haystack` matches the regular expression `pattern`. The pattern is an [re2 regular expression](https://github.com/google/re2/wiki/Syntax) which has a more limited syntax than Perl regular expressions. +## match -Returns 1 in case of a match, and 0 otherwise. +Returns whether string `haystack` matches the regular expression `pattern` in [re2 regular syntax](https://github.com/google/re2/wiki/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. -No automatic Unicode normalization is performed, you can use the [normalizeUTF8*()](https://clickhouse.com/docs/en/sql-reference/functions/string-functions/) functions for that. +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)`. -For patterns to search for substrings in a string, it is better to use functions [like](#like) or [position](#position) since they work much faster. +If you only want to search substrings in a string, you can use functions [like](#like) or [position](#position) instead - they work much faster than this function. -## multiMatchAny(haystack, \[pattern1, pattern2, …, patternn\]) +**Syntax** -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. +```sql +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 `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. +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. +(here)[https://doi.org/10.1145/3236024.3236027]. Users are adviced to check the provided patterns carefully. ::: -## multiMatchAnyIndex(haystack, \[pattern1, pattern2, …, patternn\]) +If you only want to search multiple substrings in a string, you can use function [multiSearchAny](#multisearchany) instead - it works much faster than this function. -The same as `multiMatchAny`, but returns any index that matches the haystack. +**Syntax** -## multiMatchAllIndices(haystack, \[pattern1, pattern2, …, patternn\]) +```sql +multiMatchAny(haystack, \[pattern1, pattern2, …, patternn\]) +``` -The same as `multiMatchAny`, but returns the array of all indices that match the haystack in any order. +## multiMatchAnyIndex -## multiFuzzyMatchAny(haystack, distance, \[pattern1, pattern2, …, patternn\]) +Like `multiMatchAny` but returns any index that matches the haystack. -The same as `multiMatchAny`, but returns 1 if any pattern matches the haystack within a constant [edit distance](https://en.wikipedia.org/wiki/Edit_distance). This function relies on the experimental feature of [hyperscan](https://intel.github.io/hyperscan/dev-reference/compilation.html#approximate-matching) 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. +**Syntax** -## multiFuzzyMatchAnyIndex(haystack, distance, \[pattern1, pattern2, …, patternn\]) +```sql +multiMatchAnyIndex(haystack, \[pattern1, pattern2, …, patternn\]) +``` -The same as `multiFuzzyMatchAny`, but returns any index that matches the haystack within a constant edit distance. +## multiMatchAllIndices -## multiFuzzyMatchAllIndices(haystack, distance, \[pattern1, pattern2, …, patternn\]) +Like `multiMatchAny` but returns the array of all indices that match the haystack in any order. -The same as `multiFuzzyMatchAny`, but returns the array of all indices in any order that match the haystack within a constant edit distance. +**Syntax** + +```sql +multiMatchAllIndices(haystack, \[pattern1, pattern2, …, patternn\]) +``` + +## multiFuzzyMatchAny + +Like `multiMatchAny` but returns 1 if any pattern matches the haystack within a constant [edit distance](https://en.wikipedia.org/wiki/Edit_distance). This function relies on the experimental feature of [hyperscan](https://intel.github.io/hyperscan/dev-reference/compilation.html#approximate-matching) 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*` functions do not support UTF-8 regular expressions, and such expressions are treated as bytes because of hyperscan restriction. +`multiFuzzyMatch*()` function family do not support UTF-8 regular expressions (it threats them as a sequence of bytes) due to restrictions of hyperscan. ::: -:::note -To turn off all functions that use hyperscan, use setting `SET allow_hyperscan = 0;`. -::: +**Syntax** -## extract(haystack, pattern) +```sql +multiFuzzyMatchAny(haystack, distance, \[pattern1, pattern2, …, patternn\]) +``` -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. +## multiFuzzyMatchAnyIndex -## extractAll(haystack, pattern) +Like `multiFuzzyMatchAny` but returns any index that matches the haystack within a constant edit distance. -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). +**Syntax** + +```sql +multiFuzzyMatchAnyIndex(haystack, distance, \[pattern1, pattern2, …, patternn\]) +``` + +## multiFuzzyMatchAllIndices + +Like `multiFuzzyMatchAny` but returns the array of all indices in any order that match the haystack within a constant edit distance. + +**Syntax** + +```sql +multiFuzzyMatchAllIndices(haystack, distance, \[pattern1, pattern2, …, patternn\]) +``` + +## 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** + +```sql +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** + +```sql +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. -:::note -`extractAllGroupsHorizontal` function is slower than [extractAllGroupsVertical](#extractallgroups-vertical). -::: +This function is slower than [extractAllGroupsVertical](#extractallgroups-vertical). **Syntax** @@ -468,8 +368,6 @@ If `haystack` does not match the `pattern` regex, an array of empty arrays is re **Example** -Query: - ``` sql SELECT extractAllGroupsHorizontal('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)'); ``` @@ -482,10 +380,6 @@ Result: └──────────────────────────────────────────────────────────────────────────────────────────┘ ``` -**See Also** - -- [extractAllGroupsVertical](#extractallgroups-vertical) - ## 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`. @@ -509,8 +403,6 @@ If `haystack` does not match the `pattern` regex, an empty array is returned. **Example** -Query: - ``` sql SELECT extractAllGroupsVertical('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)'); ``` @@ -523,119 +415,88 @@ Result: └────────────────────────────────────────────────────────────────────────────────────────┘ ``` -**See Also** +## like -- [extractAllGroupsHorizontal](#extractallgroups-horizontal) +Returns whether string `haystack` matches the LIKE expression `pattern`. -## 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: +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 pattern are not valid UTF-8, then the behavior is undefined. + +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*()](https://clickhouse.com/docs/en/sql-reference/functions/string-functions/) 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 `\`. +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](../syntax.md#string), 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](https://clickhouse.com/docs/en/sql-reference/functions/string-search-functions/#function-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. +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** -``` sql -ilike(haystack, pattern) +```sql +like(haystack, pattern) ``` -**Arguments** +Alias: `haystack LIKE pattern` (operator) -- `haystack` — Input string. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `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. +## notLike -Some `pattern` examples: +Like `like` but negates the result. -``` text -'abc' ILIKE 'abc' true -'abc' ILIKE 'a%' true -'abc' ILIKE '_b_' true -'abc' ILIKE 'c' false +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 that, 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 strings are similar to each other. Throws an exception if constant `needle` or `haystack` arguments are more than 32Kb in size. If any of non-constant `haystack` or `needle` arguments is more than 32Kb in size, the distance is always 1. + +Functions `ngramDistanceCaseInsensitive, ngramDistanceUTF8, ngramDistanceCaseInsensitiveUTF8` provide case-insensitive and/or UTF-8 variants of this function. + +**Syntax** + +```sql +ngramDistance(haystack, needle) ``` -**Returned values** +## ngramSearch -- True, if the string matches `pattern`. -- False, if the string does not match `pattern`. +Like `ngramDistance` but calculates the non-symmetric difference between a `needle` string and a `haystack` string, i.e. the number of n-grams from 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`. -**Example** - -Input table: - -``` text -┌─id─┬─name─────┬─days─┐ -│ 1 │ January │ 31 │ -│ 2 │ February │ 29 │ -│ 3 │ March │ 31 │ -│ 4 │ April │ 30 │ -└────┴──────────┴──────┘ -``` - -Query: - -``` sql -SELECT * FROM Months WHERE ilike(name, '%j%'); -``` - -Result: - -``` text -┌─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`. +Functions `ngramSearchCaseInsensitive, ngramSearchUTF8, ngramSearchCaseInsensitiveUTF8` provide case-insensitive and/or UTF-8 variants of this function. :::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. +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. ::: +**Syntax** + +```sql +ngramSearch(haystack, needle) +``` + ## countSubstrings -Returns the number of substring occurrences. +Returns how often substring `needle` occurs in string `haystack`. -For a case-insensitive search, use [countSubstringsCaseInsensitive](../../sql-reference/functions/string-search-functions.md#countSubstringsCaseInsensitive) or [countSubstringsCaseInsensitiveUTF8](../../sql-reference/functions/string-search-functions.md#countSubstringsCaseInsensitiveUTF8) functions. +Functions `countSubstringsCaseInsensitive` and `countSubstringsCaseInsensitiveUTF8` provide a case-insensitive and case-insensitive + UTF-8 variants of this function. **Syntax** @@ -645,34 +506,18 @@ countSubstrings(haystack, needle[, start_pos]) **Arguments** -- `haystack` — The string to search in. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — The substring to search for. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` – Position of the first character in the string to start search. Optional. [UInt](../../sql-reference/data-types/int-uint.md). +- `haystack` — String in which the search is performed. [String](../../sql-reference/syntax.md#syntax-string-literal). +- `needle` — Substring to be searched. [String](../../sql-reference/syntax.md#syntax-string-literal). +- `start_pos` – Position (1-based) in `haystack` at which the search starts. [UInt](../../sql-reference/data-types/int-uint.md). Optional. **Returned values** -- Number of occurrences. +- The number of occurrences. Type: [UInt64](../../sql-reference/data-types/int-uint.md). **Examples** -Query: - -``` sql -SELECT countSubstrings('foobar.com', '.'); -``` - -Result: - -``` text -┌─countSubstrings('foobar.com', '.')─┐ -│ 1 │ -└────────────────────────────────────┘ -``` - -Query: - ``` sql SELECT countSubstrings('aaaa', 'aa'); ``` @@ -685,7 +530,7 @@ Result: └───────────────────────────────┘ ``` -Query: +Example with `start_pos` argument: ```sql SELECT countSubstrings('abc___abc', 'abc', 4); @@ -699,125 +544,7 @@ Result: └────────────────────────────────────────┘ ``` -## countSubstringsCaseInsensitive - -Returns the number of substring occurrences case-insensitive. - -**Syntax** - -``` sql -countSubstringsCaseInsensitive(haystack, needle[, start_pos]) -``` - -**Arguments** - -- `haystack` — The string to search in. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — The substring to search for. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` — Position of the first character in the string to start search. Optional. [UInt](../../sql-reference/data-types/int-uint.md). - -**Returned values** - -- Number of occurrences. - -Type: [UInt64](../../sql-reference/data-types/int-uint.md). - -**Examples** - -Query: - -``` sql -SELECT countSubstringsCaseInsensitive('aba', 'B'); -``` - -Result: - -``` text -┌─countSubstringsCaseInsensitive('aba', 'B')─┐ -│ 1 │ -└────────────────────────────────────────────┘ -``` - -Query: - -``` sql -SELECT countSubstringsCaseInsensitive('foobar.com', 'CoM'); -``` - -Result: - -``` text -┌─countSubstringsCaseInsensitive('foobar.com', 'CoM')─┐ -│ 1 │ -└─────────────────────────────────────────────────────┘ -``` - -Query: - -``` sql -SELECT countSubstringsCaseInsensitive('abC___abC', 'aBc', 2); -``` - -Result: - -``` text -┌─countSubstringsCaseInsensitive('abC___abC', 'aBc', 2)─┐ -│ 1 │ -└───────────────────────────────────────────────────────┘ -``` - -## countSubstringsCaseInsensitiveUTF8 - -Returns the number of substring occurrences in `UTF-8` case-insensitive. - -**Syntax** - -``` sql -SELECT countSubstringsCaseInsensitiveUTF8(haystack, needle[, start_pos]) -``` - -**Arguments** - -- `haystack` — The string to search in. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `needle` — The substring to search for. [String](../../sql-reference/syntax.md#syntax-string-literal). -- `start_pos` — Position of the first character in the string to start search. Optional. [UInt](../../sql-reference/data-types/int-uint.md). - -**Returned values** - -- Number of occurrences. - -Type: [UInt64](../../sql-reference/data-types/int-uint.md). - -**Examples** - -Query: - -``` sql -SELECT countSubstringsCaseInsensitiveUTF8('абв', 'A'); -``` - -Result: - -``` text -┌─countSubstringsCaseInsensitiveUTF8('абв', 'A')─┐ -│ 1 │ -└────────────────────────────────────────────────┘ -``` - -Query: - -```sql -SELECT countSubstringsCaseInsensitiveUTF8('аБв__АбВ__абв', 'Абв'); -``` - -Result: - -``` text -┌─countSubstringsCaseInsensitiveUTF8('аБв__АбВ__абв', 'Абв')─┐ -│ 3 │ -└────────────────────────────────────────────────────────────┘ -``` - -## countMatches(haystack, pattern) +## countMatches Returns the number of regular expression matches for a `pattern` in a `haystack`. @@ -840,8 +567,6 @@ Type: [UInt64](../../sql-reference/data-types/int-uint.md). **Examples** -Query: - ``` sql SELECT countMatches('foobar.com', 'o+'); ``` @@ -854,8 +579,6 @@ Result: └──────────────────────────────────┘ ``` -Query: - ``` sql SELECT countMatches('aaaa', 'aa'); ``` @@ -868,7 +591,7 @@ Result: └───────────────────────────────┘ ``` -## regexpExtract(haystack, pattern[, index]) +## regexpExtract Extracts the first string in haystack that matches the regexp pattern and corresponds to the regex group index. @@ -899,8 +622,12 @@ 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+)'); +``` +Result: + +``` text ┌─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 │ └──────────────────────────────────────────────┴──────────────────────────────────────────────┴──────────────────────────────────────────────┴───────────────────────────────────────────┘