0a4a5b36cc
* 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 working with strings
empty
Returns 1 for an empty string or 0 for a non-empty string. The result type is UInt8. A string is considered non-empty if it contains at least one byte, even if this is a space or a null byte. The function also works for arrays.
notEmpty
Returns 0 for an empty string or 1 for a non-empty string. The result type is UInt8. The function also works for arrays.
length
Returns the length of a string in bytes (not in characters, and not in code points). The result type is UInt64. The function also works for arrays.
lengthUTF8
Returns the length of a string in Unicode code points (not in characters), assuming that the string contains a set of bytes that make up UTF-8 encoded text. If this assumption is not met, it returns some result (it doesn't throw an exception). The result type is UInt64.
lower
Converts ASCII Latin symbols in a string to lowercase.
upper
Converts ASCII Latin symbols in a string to uppercase.
lowerUTF8
Converts a string to lowercase, assuming the string contains a set of bytes that make up a UTF-8 encoded text. It doesn't detect the language. So for Turkish the result might not be exactly correct. If the length of the UTF-8 byte sequence is different for upper and lower case of a code point, the result may be incorrect for this code point. If the string contains a set of bytes that is not UTF-8, then the behavior is undefined.
upperUTF8
Converts a string to uppercase, assuming the string contains a set of bytes that make up a UTF-8 encoded text. It doesn't detect the language. So for Turkish the result might not be exactly correct. If the length of the UTF-8 byte sequence is different for upper and lower case of a code point, the result may be incorrect for this code point. If the string contains a set of bytes that is not UTF-8, then the behavior is undefined.
reverse
Reverses the string (as a sequence of bytes).
reverseUTF8
Reverses a sequence of Unicode code points, assuming that the string contains a set of bytes representing a UTF-8 text. Otherwise, it does something else (it doesn't throw an exception).
concat(s1, s2, ...)
Concatenates the strings listed in the arguments, without a separator.
substring(s, offset, length)
Returns a substring starting with the byte from the 'offset' index that is 'length' bytes long. Character indexing starts from one (as in standard SQL). The 'offset' and 'length' arguments must be constants.
substringUTF8(s, offset, length)
The same as 'substring', but for 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).
appendTrailingCharIfAbsent(s, c)
If the 's' string is non-empty and does not contain the 'c' character at the end, it appends the 'c' character to the end.
convertCharset(s, from, to)
Returns the string 's' that was converted from the encoding in 'from' to the encoding in 'to'.