thevar1able/ClickHouse
1
0
Fork 0
mirror of https://github.com/ClickHouse/ClickHouse.git synced 2024-11-27 18:12:02 +00:00
Code Issues Packages Projects Releases Wiki Activity
6273176dca
ClickHouse/docs/en/sql-reference/functions/string-search-functions.md
Robert Schulze 74937cf27b
Reject DoS-prone hyperscan regexes
2023-02-09 17:17:35 +00:00

866 lines
32 KiB
Markdown
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

---
slug: /en/sql-reference/functions/string-search-functions
sidebar_position: 41
sidebar_label: For 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](../../sql-reference/functions/string-replace-functions.md) and [other manipulations with strings](../../sql-reference/functions/string-functions.md) 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](#positioncaseinsensitive).
**Syntax**
``` sql
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)`.
:::
**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` – Position of the first character in the string to start search. [UInt](../../sql-reference/data-types/int-uint.md). 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:
``` sql
SELECT position('Hello, world!', '!');
```
Result:
``` text
┌─position('Hello, world!', '!')─┐
│ 13 │
└────────────────────────────────┘
```
``` sql
SELECT
position('Hello, world!', 'o', 1),
position('Hello, world!', 'o', 7)
```
``` text
┌─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](#positionutf8) function for multi-byte encoded text):
Query:
``` sql
SELECT position('Привет, мир!', '!');
```
Result:
``` text
┌─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`
``` sql
SELECT
position('abc', ''),
position('abc', '', 0),
position('abc', '', 1),
position('abc', '', 2),
position('abc', '', 3),
position('abc', '', 4),
position('abc', '', 5)
```
``` text
┌─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:
```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 │
└───────────────────────────────────────────────────┘
```
## 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`.
**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:
``` sql
SELECT positionUTF8('Привет, мир!', '!');
```
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 │
└────────────────────────────────────────┘
```
## 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 │
└────────────────────────────────────────────────────┘
```
## 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.
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.
**Syntax**
``` sql
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).
**Returned values**
- Array of starting positions in bytes (counting from 1), if the corresponding substring was found and 0 if not found.
**Example**
Query:
``` sql
SELECT multiSearchAllPositions('Hello, World!', ['hello', '!', 'world']);
```
Result:
``` text
┌─multiSearchAllPositions('Hello, World!', ['hello', '!', 'world'])─┐
│ [0,13,0] │
└───────────────────────────────────────────────────────────────────┘
```
## multiSearchAllPositionsUTF8
See `multiSearchAllPositions`.
## multiSearchFirstPosition(haystack, \[needle<sub>1</sub>, needle<sub>2</sub>, …, needle<sub>n</sub>\])
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, \[needle<sub>1</sub>, needle<sub>2</sub>, …, needle<sub>n</sub>\])
Returns the index `i` (starting from 1) of the leftmost found needle<sub>i</sub> 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, \[needle<sub>1</sub>, needle<sub>2</sub>, …, needle<sub>n</sub>\])
Returns 1, if at least one string needle<sub>i</sub> 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 2<sup>8</sup> because of implementation specification.
:::
## match(haystack, pattern)
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.
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 pattern contain a sequence of bytes that are not valid UTF-8, the behavior is undefined.
No automatic Unicode normalization is performed, if you need it you can use the [normalizeUTF8*()](https://clickhouse.com/docs/en/sql-reference/functions/string-functions/) 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 LIKE or ‘position’, since they work much faster.
## multiMatchAny(haystack, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
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 2<sup>32</sup> 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, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
The same as `multiMatchAny`, but returns any index that matches the haystack.
## multiMatchAllIndices(haystack, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
The same as `multiMatchAny`, but returns the array of all indices that match the haystack in any order.
## multiFuzzyMatchAny(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
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.
## multiFuzzyMatchAnyIndex(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
The same as `multiFuzzyMatchAny`, but returns any index that matches the haystack within a constant edit distance.
## multiFuzzyMatchAllIndices(haystack, distance, \[pattern<sub>1</sub>, pattern<sub>2</sub>, …, pattern<sub>n</sub>\])
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](#extractallgroups-vertical).
:::
**Syntax**
``` sql
extractAllGroupsHorizontal(haystack, pattern)
```
**Arguments**
- `haystack` — Input string. Type: [String](../../sql-reference/data-types/string.md).
- `pattern` — Regular expression with [re2 syntax](https://github.com/google/re2/wiki/Syntax). Must contain groups, each group enclosed in parentheses. If `pattern` contains no groups, an exception is thrown. Type: [String](../../sql-reference/data-types/string.md).
**Returned value**
- Type: [Array](../../sql-reference/data-types/array.md).
If `haystack` does not match the `pattern` regex, an array of empty arrays is returned.
**Example**
Query:
``` sql
SELECT extractAllGroupsHorizontal('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)');
```
Result:
``` text
┌─extractAllGroupsHorizontal('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)')─┐
│ [['abc','def','ghi'],['111','222','333']] │
└──────────────────────────────────────────────────────────────────────────────────────────┘
```
**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`.
**Syntax**
``` sql
extractAllGroupsVertical(haystack, pattern)
```
**Arguments**
- `haystack` — Input string. Type: [String](../../sql-reference/data-types/string.md).
- `pattern` — Regular expression with [re2 syntax](https://github.com/google/re2/wiki/Syntax). Must contain groups, each group enclosed in parentheses. If `pattern` contains no groups, an exception is thrown. Type: [String](../../sql-reference/data-types/string.md).
**Returned value**
- Type: [Array](../../sql-reference/data-types/array.md).
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+)');
```
Result:
``` text
┌─extractAllGroupsVertical('abc=111, def=222, ghi=333', '("[^"]+"|\\w+)=("[^"]+"|\\w+)')─┐
│ [['abc','111'],['def','222'],['ghi','333']] │
└────────────────────────────────────────────────────────────────────────────────────────┘
```
**See Also**
- [extractAllGroupsHorizontal](#extractallgroups-horizontal)
## like(haystack, pattern), haystack LIKE pattern operator
Checks whether a string matches a simple regular expression.
The regular expression can contain the metasymbols `%` and `_`.
`%` indicates any quantity of any bytes (including zero characters).
`_` indicates any one byte.
Use the backslash (`\`) for escaping metasymbols. See the note on escaping in the description of the ‘match’ function.
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 pattern contain a sequence of bytes that are not valid UTF-8, then the behavior is undefined.
No automatic Unicode normalization is performed, if you need it you can use the [normalizeUTF8*()](https://clickhouse.com/docs/en/sql-reference/functions/string-functions/) functions for that.
For regular expressions like `%needle%`, the code is more optimal and works as fast as the `position` function.
For other regular expressions, the code is the same as for the ‘match’ function.
## 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.
**Syntax**
``` sql
ilike(haystack, pattern)
```
**Arguments**
- `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.
Some `pattern` examples:
``` text
'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:
``` 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 │
└────┴─────────┴──────┘
```
**See Also**
## 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](../../sql-reference/functions/string-search-functions.md#countSubstringsCaseInsensitive) or [countSubstringsCaseInsensitiveUTF8](../../sql-reference/functions/string-search-functions.md#countSubstringsCaseInsensitiveUTF8) functions.
**Syntax**
``` sql
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).
**Returned values**
- 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');
```
Result:
``` text
┌─countSubstrings('aaaa', 'aa')─┐
│ 2 │
└───────────────────────────────┘
```
Query:
```sql
SELECT countSubstrings('abc___abc', 'abc', 4);
```
Result:
``` text
┌─countSubstrings('abc___abc', 'abc', 4)─┐
│ 1 │
└────────────────────────────────────────┘
```
## 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)
Returns the number of regular expression matches for a `pattern` in a `haystack`.
**Syntax**
``` sql
countMatches(haystack, pattern)
```
**Arguments**
- `haystack` — The string to search in. [String](../../sql-reference/syntax.md#syntax-string-literal).
- `pattern` — The regular expression with [re2 syntax](https://github.com/google/re2/wiki/Syntax). [String](../../sql-reference/data-types/string.md).
**Returned value**
- The number of matches.
Type: [UInt64](../../sql-reference/data-types/int-uint.md).
**Examples**
Query:
``` sql
SELECT countMatches('foobar.com', 'o+');
```
Result:
``` text
┌─countMatches('foobar.com', 'o+')─┐
│ 2 │
└──────────────────────────────────┘
```
Query:
``` sql
SELECT countMatches('aaaa', 'aa');
```
Result:
``` text
┌─countMatches('aaaa', 'aa')────┐
│ 2 │
└───────────────────────────────┘
```
Reference in New Issue View Git Blame Copy Permalink