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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 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 needle substring in the haystack string.
Returns the position (in bytes) of the found substring, starting from 1, or returns 0 if the substring was not found.
For case-insensitive search use positionCaseInsensitive function.
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 case-insensitive search use positionCaseInsensitiveUTF8 function.
match(haystack, pattern)
Checks whether the string matches the 'pattern' regular expression. A re2 regular expression. 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.