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* Update of english version of descriprion of the table function `file`. * New syntax for ReplacingMergeTree. Some improvements in text. * Significantly change article about SummingMergeTree. Article is restructured, text is changed in many places of the document. New syntax for table creation is described. * Descriptions of AggregateFunction and AggregatingMergeTree are updated. Russian version. * New syntax for new syntax of CREATE TABLE * Added english docs on Aggregating, Replacing and SummingMergeTree. * CollapsingMergeTree docs. English version. * 1. Update of CollapsingMergeTree. 2. Minor changes in markup * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatingmergetree.md * GraphiteMergeTree docs update. New syntax for creation of Replicated* tables. Minor changes in *MergeTree tables creation syntax. * Markup fix * Markup and language fixes * Clarification in the CollapsingMergeTree article * DOCAPI-4821. Sync between ru and en versions of docs. * Fixed the ambiguity in geo functions description. * Example of JOIN in ru docs * Deleted misinforming example.
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Functions for searching strings
The search is case-sensitive in all these functions. The search substring or regular expression must be a constant in all these functions.
position(haystack, needle)
Search for the substring needle in the string haystack.
Returns the position (in bytes) of the found substring, starting from 1, or returns 0 if the substring was not found.
For a case-insensitive search, use the function positionCaseInsensitive.
positionUTF8(haystack, needle)
The same as position, but the position is returned in Unicode code points. Works under the assumption that the string contains a set of bytes representing a UTF-8 encoded text. If this assumption is not met, it returns some result (it doesn't throw an exception).
For a case-insensitive search, use the function positionCaseInsensitiveUTF8.
match(haystack, pattern)
Checks whether the string matches the pattern regular expression. A re2 regular expression. The syntax of the re2 regular expressions is more limited than the syntax of the Perl regular expressions.
Returns 0 if it doesn't match, or 1 if it matches.
Note that the backslash symbol (\) is used for escaping in the regular expression. The same symbol is used for escaping in string literals. So in order to escape the symbol in a regular expression, you must write two backslashes (\) in a string literal.
The regular expression works with the string as if it is a set of bytes. The regular expression can't contain null bytes. For patterns to search for substrings in a string, it is better to use LIKE or 'position', since they work much faster.
extract(haystack, pattern)
Extracts a fragment of a string using a regular expression. If 'haystack' doesn't match the 'pattern' regex, an empty string is returned. If the regex doesn't contain subpatterns, it takes the fragment that matches the entire regex. Otherwise, it takes the fragment that matches the first subpattern.
extractAll(haystack, pattern)
Extracts all the fragments of a string using a regular expression. If 'haystack' doesn't match the 'pattern' regex, an empty string is returned. Returns an array of strings consisting of all matches to the regex. In general, the behavior is the same as the 'extract' function (it takes the first subpattern, or the entire expression if there isn't a subpattern).
like(haystack, pattern), haystack LIKE pattern operator
Checks whether a string matches a simple regular expression.
The regular expression can contain the metasymbols % and _.
``% indicates any quantity of any bytes (including zero characters).
_ indicates any one byte.
Use the backslash (\) for escaping metasymbols. See the note on escaping in the description of the 'match' function.
For regular expressions like %needle%, the code is more optimal and works as fast as the position function.
For other regular expressions, the code is the same as for the 'match' function.
notLike(haystack, pattern), haystack NOT LIKE pattern operator
The same thing as 'like', but negative.