ClickHouse/docs/en/functions/string_replace_functions.rst
Andrey Dudin e3f8647a75 Functions
2017-04-27 23:16:22 +03:00

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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.
The substitutions \1-\9 include the subpattern corresponding to the number.
In order to specify the \ symbol in a pattern, you must use a \ symbol to escape it.
Also keep in mind that a string literal requires an extra escape.
Example 1. Converting the date to American format:
.. code-block:: sql
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. Copy the string ten times:
.. code-block:: sql
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:
.. code-block:: sql
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:
.. code-block:: sql
SELECT replaceRegexpAll('Hello, World!', '^', 'here: ') AS res
┌─res─────────────────┐
│ here: Hello, World! │
└─────────────────────┘