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130 lines
5.1 KiB
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130 lines
5.1 KiB
Markdown
---
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slug: /en/sql-reference/functions/string-replace-functions
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sidebar_position: 42
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sidebar_label: For Replacing in Strings
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---
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# Functions for Searching and Replacing in Strings
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:::note
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Functions for [searching](../../sql-reference/functions/string-search-functions.md) and [other manipulations with strings](../../sql-reference/functions/string-functions.md) are described separately.
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:::
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## replaceOne(haystack, pattern, replacement)
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Replaces the first occurrence of the substring ‘pattern’ (if it exists) in ‘haystack’ by the ‘replacement’ string.
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‘pattern’ and ‘replacement’ must be constants.
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## replaceAll(haystack, pattern, replacement), replace(haystack, pattern, replacement)
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Replaces all occurrences of the substring ‘pattern’ in ‘haystack’ by the ‘replacement’ string.
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## replaceRegexpOne(haystack, pattern, replacement)
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Replaces the first occurrence of the substring matching the regular expression ‘pattern’ in ‘haystack‘ by the ‘replacement‘ string.
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‘pattern‘ must be a constant [re2 regular expression](https://github.com/google/re2/wiki/Syntax).
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‘replacement’ must be a plain constant string or a constant string containing substitutions `\0-\9`.
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Substitutions `\1-\9` correspond to the 1st to 9th capturing group (submatch), substitution `\0` corresponds to the entire match.
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To use a verbatim `\` character in the ‘pattern‘ or ‘replacement‘ string, escape it using `\`.
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Also keep in mind that string literals require an extra escaping.
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Example 1. Converting ISO dates to American format:
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``` sql
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SELECT DISTINCT
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EventDate,
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replaceRegexpOne(toString(EventDate), '(\\d{4})-(\\d{2})-(\\d{2})', '\\2/\\3/\\1') AS res
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FROM test.hits
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LIMIT 7
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FORMAT TabSeparated
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```
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``` text
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2014-03-17 03/17/2014
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2014-03-18 03/18/2014
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2014-03-19 03/19/2014
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2014-03-20 03/20/2014
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2014-03-21 03/21/2014
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2014-03-22 03/22/2014
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2014-03-23 03/23/2014
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```
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Example 2. Copying a string ten times:
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``` sql
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SELECT replaceRegexpOne('Hello, World!', '.*', '\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0') AS res
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```
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``` text
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┌─res────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
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│ Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World! │
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└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
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```
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## replaceRegexpAll(haystack, pattern, replacement)
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Like ‘replaceRegexpOne‘, but replaces all occurrences of the pattern. Example:
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``` sql
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SELECT replaceRegexpAll('Hello, World!', '.', '\\0\\0') AS res
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```
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``` text
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┌─res────────────────────────┐
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│ HHeelllloo,, WWoorrlldd!! │
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└────────────────────────────┘
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```
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As an exception, if a regular expression worked on an empty substring, the replacement is not made more than once.
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Example:
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``` sql
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SELECT replaceRegexpAll('Hello, World!', '^', 'here: ') AS res
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```
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``` text
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┌─res─────────────────┐
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│ here: Hello, World! │
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└─────────────────────┘
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```
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## regexpQuoteMeta(s)
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The function adds a backslash before some predefined characters in the string.
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Predefined characters: `\0`, `\\`, `|`, `(`, `)`, `^`, `$`, `.`, `[`, `]`, `?`, `*`, `+`, `{`, `:`, `-`.
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This implementation slightly differs from re2::RE2::QuoteMeta. It escapes zero byte as `\0` instead of `\x00` and it escapes only required characters.
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For more information, see the link: [RE2](https://github.com/google/re2/blob/master/re2/re2.cc#L473)
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## translate(s, from, to)
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The function replaces characters in the string ‘s’ in accordance with one-to-one character mapping defined by ‘from’ and ‘to’ strings. ‘from’ and ‘to’ must be constant ASCII strings of the same size. Non-ASCII characters in the original string are not modified.
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Example:
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``` sql
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SELECT translate('Hello, World!', 'delor', 'DELOR') AS res
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```
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``` text
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┌─res───────────┐
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│ HELLO, WORLD! │
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└───────────────┘
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```
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## translateUTF8(string, from, to)
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Similar to previous function, but works with UTF-8 arguments. ‘from’ and ‘to’ must be valid constant UTF-8 strings of the same size.
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Example:
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``` sql
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SELECT translateUTF8('Hélló, Wórld¡', 'óé¡', 'oe!') AS res
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```
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``` text
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┌─res───────────┐
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│ Hello, World! │
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└───────────────┘
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```
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