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* Additional .gitignore entries * Merge a bunch of small articles about system tables into single one * Merge a bunch of small articles about formats into single one * Adapt table with formats to English docs too * Add SPb meetup link to main page * Move Utilities out of top level of docs (the location is probably not yet final) + translate couple articles * Merge MacOS.md into build_osx.md * Move Data types higher in ToC * Publish changelog on website alongside documentation * Few fixes for en/table_engines/file.md * Use smaller header sizes in changelogs * Group up table engines inside ToC * Move table engines out of top level too * Specificy in ToC that query language is SQL based. Thats a bit excessive, but catches eye. * Move stuff that is part of query language into respective folder * Move table functions lower in ToC * Lost redirects.txt update * Do not rely on comments in yaml + fix few ru titles * Extract major parts of queries.md into separate articles * queries.md has been supposed to be removed * Fix weird translation * Fix a bunch of links * There is only table of contents left * "Query language" is actually part of SQL abbreviation * Change filename in README.md too * fix mistype
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Functions for searching and replacing in strings
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)
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! │
└─────────────────────┘