4.9 KiB
| sidebar_position | sidebar_label |
|---|---|
| 42 | For Replacing in Strings |
Functions for Searching and Replacing in Strings
:::note
Functions for searching and other manipulations with strings are described separately.
:::
replaceOne(haystack, pattern, replacement)
Replaces the first occurrence, if it exists, of the ‘pattern’ substring in ‘haystack’ with the ‘replacement’ substring. Hereafter, ‘pattern’ and ‘replacement’ must be constants.
replaceAll(haystack, pattern, replacement), replace(haystack, pattern, replacement)
Replaces all occurrences of the ‘pattern’ substring in ‘haystack’ with the ‘replacement’ substring.
replaceRegexpOne(haystack, pattern, replacement)
Replacement using the ‘pattern’ regular expression. A re2 regular expression.
Replaces only the first occurrence, if it exists.
A pattern can be specified as ‘replacement’. This pattern can include substitutions \0-\9.
The substitution \0 includes the entire regular expression. Substitutions \1-\9 correspond to the subpattern numbers.To use the \ character in a template, escape it using \.
Also keep in mind that a string literal requires an extra escape.
Example 1. Converting the date to American format:
SELECT DISTINCT
EventDate,
replaceRegexpOne(toString(EventDate), '(\\d{4})-(\\d{2})-(\\d{2})', '\\2/\\3/\\1') AS res
FROM test.hits
LIMIT 7
FORMAT TabSeparated
2014-03-17 03/17/2014
2014-03-18 03/18/2014
2014-03-19 03/19/2014
2014-03-20 03/20/2014
2014-03-21 03/21/2014
2014-03-22 03/22/2014
2014-03-23 03/23/2014
Example 2. Copying a string ten times:
SELECT replaceRegexpOne('Hello, World!', '.*', '\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0') AS res
┌─res────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World! │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
replaceRegexpAll(haystack, pattern, replacement)
This does the same thing, but replaces all the occurrences. Example:
SELECT replaceRegexpAll('Hello, World!', '.', '\\0\\0') AS res
┌─res────────────────────────┐
│ HHeelllloo,, WWoorrlldd!! │
└────────────────────────────┘
As an exception, if a regular expression worked on an empty substring, the replacement is not made more than once. Example:
SELECT replaceRegexpAll('Hello, World!', '^', 'here: ') AS res
┌─res─────────────────┐
│ here: Hello, World! │
└─────────────────────┘
regexpQuoteMeta(s)
The function adds a backslash before some predefined characters in the string.
Predefined characters: \0, \\, |, (, ), ^, $, ., [, ], ?, *, +, {, :, -.
This implementation slightly differs from re2::RE2::QuoteMeta. It escapes zero byte as \0 instead of \x00 and it escapes only required characters.
For more information, see the link: RE2
translate(s, from, to)
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.
Example:
SELECT translate('Hello, World!', 'delor', 'DELOR') AS res
┌─res───────────┐
│ HELLO, WORLD! │
└───────────────┘
translateUTF8(string, from, to)
Similar to previous function, but works with UTF-8 arguments. ‘from’ and ‘to’ must be valid constant UTF-8 strings of the same size.
Example:
SELECT translateUTF8('Hélló, Wórld¡', 'óé¡', 'oe!') AS res
┌─res───────────┐
│ Hello, World! │
└───────────────┘