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81 lines
3.6 KiB
ReStructuredText
81 lines
3.6 KiB
ReStructuredText
Functions for searching and replacing in strings
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------------------------------------------------
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replaceOne(haystack, pattern, replacement)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Replaces the first occurrence, if it exists, of the 'pattern' substring in 'haystack' with the 'replacement' substring.
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Hereafter, 'pattern' and 'replacement' must be constants.
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replaceAll(haystack, pattern, replacement)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Replaces all occurrences of the 'pattern' substring in 'haystack' with the 'replacement' substring.
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replaceRegexpOne(haystack, pattern, replacement)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Replacement using the 'pattern' regular expression. A re2 regular expression. Replaces only the first occurrence, if it exists.
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A pattern can be specified as 'replacement'. This pattern can include substitutions \0-\9\.
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The substitution \0 includes the entire regular expression.
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The substitutions \1-\9 include the subpattern corresponding to the number.
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In order to specify the \ symbol in a pattern, you must use a \ symbol to escape it.
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Also keep in mind that a string literal requires an extra escape.
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Example 1. Converting the date to American format:
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.. code-block:: 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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.. code-block:: 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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Example 2. Copy the string ten times:
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.. code-block:: 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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.. code-block:: 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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replaceRegexpAll(haystack, pattern, replacement)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This does the same thing, but replaces all the occurrences. Example:
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.. code-block:: sql
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SELECT replaceRegexpAll('Hello, World!', '.', '\\0\\0') AS res
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.. code-block:: text
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┌─res────────────────────────┐
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│ HHeelllloo,, WWoorrlldd!! │
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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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.. code-block:: sql
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SELECT replaceRegexpAll('Hello, World!', '^', 'here: ') AS res
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.. code-block:: text
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┌─res─────────────────┐
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│ here: Hello, World! │
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└─────────────────────┘
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