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Posted to github@arrow.apache.org by "alamb (via GitHub)" <gi...@apache.org> on 2023/04/12 19:43:15 UTC
[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #5978: docs: improve expressions.md
alamb commented on code in PR #5978:
URL: https://github.com/apache/arrow-datafusion/pull/5978#discussion_r1164565331
##########
docs/source/user-guide/expressions.md:
##########
@@ -125,105 +135,105 @@ Unlike to some databases the math functions in Datafusion works the same way as
## String Expressions
-| Function | Notes |
-| ---------------- | ----- |
-| ascii | |
-| bit_length | |
-| btrim | |
-| char_length | |
-| character_length | |
-| concat | |
-| concat_ws | |
-| chr | |
-| initcap | |
-| left | |
-| length | |
-| lower | |
-| lpad | |
-| ltrim | |
-| md5 | |
-| octet_length | |
-| repeat | |
-| replace | |
-| reverse | |
-| right | |
-| rpad | |
-| rtrim | |
-| digest | |
-| split_part | |
-| starts_with | |
-| strpos | |
-| substr | |
-| translate | |
-| trim | |
-| upper | |
+| Function | Notes |
+| ---------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| ascii(character) | Returns a numeric representation of the character (`character`). Example: `ascii('a') -> 97` |
+| bit_length(text) | Returns the length of the string (`text`) in bits. Example: `bit_length('spider') -> 48` |
+| btrim(text, characters) | Removes all specified characters (`characters`) from both the beginning and the end of the string (`text`). Example: `btrim('aabchelloccb', 'abc') -> hello` |
+| char_length(text) | Returns number of characters in the string (`text`). The same as `character_length` and `length`. Example: `character_length('lion') -> 4` |
+| character_length(text) | Returns number of characters in the string (`text`). The same as `char_length` and `length`. Example: `char_length('lion') -> 4` |
+| concat(value1, [value2 [, ...]]) | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments. NULL arguments are ignored. Example: `concat('aaa', 'bbc', NULL, 321) -> aaabbc321` |
+| concat_ws(separator, value1, [value2 [, ...]]) | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments with the separator (`separator`). NULL arguments are ignored. `concat_ws('/', 'path', 'to', NULL, 'my', 'folder', 123) -> path/to/my/folder/123` |
+| chr(integer) | Returns a character by its numeric representation (`integer`). Example: `chr(90) -> 8` |
+| initcap | Converts the first letter of each word to upper case and the rest to lower case. Example: `initcap('hi TOM') -> Hi Tom` |
+| left(text, number) | Returns a certain number (`number`) of first characters (`text`). Example: `left('like', 2) -> li` |
+| length(text) | Returns number of characters in the string (`text`). The same as `character_length` and `char_length`. Example: `length('lion') -> 4` |
+| lower(text) | Converts all characters in the string (`text`) into lower case. Example: `lower('HELLO') -> hello` |
+| lpad(text, length, [, fill]) | Extends the string to length (`lenght`) by prepending the characters (`fill`) (a space by default). Example: `lpad('bb', 5, 'a') → aaabb` |
Review Comment:
```suggestion
| lpad(text, length, [, fill]) | Extends the string to length (`length`) by prepending the characters (`fill`) (a space by default). Example: `lpad('bb', 5, 'a') → aaabb` |
```
##########
docs/source/user-guide/expressions.md:
##########
@@ -125,105 +135,105 @@ Unlike to some databases the math functions in Datafusion works the same way as
## String Expressions
-| Function | Notes |
-| ---------------- | ----- |
-| ascii | |
-| bit_length | |
-| btrim | |
-| char_length | |
-| character_length | |
-| concat | |
-| concat_ws | |
-| chr | |
-| initcap | |
-| left | |
-| length | |
-| lower | |
-| lpad | |
-| ltrim | |
-| md5 | |
-| octet_length | |
-| repeat | |
-| replace | |
-| reverse | |
-| right | |
-| rpad | |
-| rtrim | |
-| digest | |
-| split_part | |
-| starts_with | |
-| strpos | |
-| substr | |
-| translate | |
-| trim | |
-| upper | |
+| Function | Notes |
+| ---------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| ascii(character) | Returns a numeric representation of the character (`character`). Example: `ascii('a') -> 97` |
+| bit_length(text) | Returns the length of the string (`text`) in bits. Example: `bit_length('spider') -> 48` |
+| btrim(text, characters) | Removes all specified characters (`characters`) from both the beginning and the end of the string (`text`). Example: `btrim('aabchelloccb', 'abc') -> hello` |
+| char_length(text) | Returns number of characters in the string (`text`). The same as `character_length` and `length`. Example: `character_length('lion') -> 4` |
+| character_length(text) | Returns number of characters in the string (`text`). The same as `char_length` and `length`. Example: `char_length('lion') -> 4` |
+| concat(value1, [value2 [, ...]]) | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments. NULL arguments are ignored. Example: `concat('aaa', 'bbc', NULL, 321) -> aaabbc321` |
+| concat_ws(separator, value1, [value2 [, ...]]) | Concatenates the text representations (`value1, [value2 [, ...]]`) of all the arguments with the separator (`separator`). NULL arguments are ignored. `concat_ws('/', 'path', 'to', NULL, 'my', 'folder', 123) -> path/to/my/folder/123` |
+| chr(integer) | Returns a character by its numeric representation (`integer`). Example: `chr(90) -> 8` |
+| initcap | Converts the first letter of each word to upper case and the rest to lower case. Example: `initcap('hi TOM') -> Hi Tom` |
+| left(text, number) | Returns a certain number (`number`) of first characters (`text`). Example: `left('like', 2) -> li` |
+| length(text) | Returns number of characters in the string (`text`). The same as `character_length` and `char_length`. Example: `length('lion') -> 4` |
+| lower(text) | Converts all characters in the string (`text`) into lower case. Example: `lower('HELLO') -> hello` |
+| lpad(text, length, [, fill]) | Extends the string to length (`lenght`) by prepending the characters (`fill`) (a space by default). Example: `lpad('bb', 5, 'a') → aaabb` |
+| ltrim(text, text) | Removes all specified characters (`characters`) from the beginning of the string (`text`). Example: `ltrim('aabchelloccb', 'abc') -> helloccb` |
+| md5(text) | Computes the MD5 hash of the argument (`text`). |
+| octet_length(text) | Returns number of bytes in the string (`text`). |
+| repeat(text, number) | Repeats the string the specified number of times. Example: `repeat('1', 4) -> 1111` |
+| replace(string, from, to) | Replaces a specified string (`from`) with another specified string (`to`) in the string (`string`). Example: `replace('Hello', 'replace', 'el') -> Hola` |
+| reverse(text) | Reverses the order of the characters in the string (`text`). Example: `reverse('hello') -> olleh` |
+| right(text, number) | Returns a certain number (`number`) of last characters (`text`). Example: `right('like', 2) -> ke` |
+| rpad(text, length, [, fill]) | Extends the string to length (`lenght`) by prepending the characters (`fill`) (a space by default). Example: `rpad('bb', 5, 'a') → bbaaa` |
+| rtrim | Removes all specified characters (`characters`) from the end of the string (`text`). Example: `rtrim('aabchelloccb', 'abc') -> aabchello` |
+| digest(input, algorithm) | Computes the binary hash of `input`, using the `algorithm`. |
+| split_part(string, delimiter, index) | Splits the string (`string`) based on a delimiter (`delimiter`) and picks out the desired field based on the index (`index`). |
+| starts_with(string, prefix) | Returns `true` if the string (`string`) starts with the specified prefix (`prefix`). If not, it returns `false`. Example: `starts_with('Hi Tom', 'Hi') -> true` |
+| strpos | Finds the position from where the `substring` matches the `string` |
+| substr(string, position, [, length]) | Returns substring from the position (`position`) with length (`length`) characters in the string (`string`). |
+| translate(string, from, to) | Replaces the characters in `from` with the counterpart in `to`. Example: `translate('abcde', 'acd', '15') -> 1b5e` |
+| trim(string) | Removes all characters, space by default from the string (`string`) |
+| upper | Converts all characters in the string into upper case. Example: `upper('hello') -> HELLO` |
## Regular Expressions
-| Function | Notes |
-| -------------- | ----- |
-| regexp_match | |
-| regexp_replace | |
+| Function | Notes |
+| -------------- | ----------------------------------------------------------------------------- |
+| regexp_match | Matches a regular expression against a string and returns matched substrings. |
+| regexp_replace | Replaces strings that match a regular expression |
## Temporal Expressions
-| Function | Notes |
-| -------------------- | ------------ |
-| date_part | |
-| date_trunc | |
-| from_unixtime | |
-| to_timestamp | |
-| to_timestamp_millis | |
-| to_timestamp_micros | |
-| to_timestamp_seconds | |
-| now() | current time |
+| Function | Notes |
+| -------------------- | ------------------------------------------------------ |
+| date_part | Extracts a subfield from the date. |
+| date_trunc | Truncates the date to a specified level of precision. |
+| from_unixtime | Returns the unix time in format. |
+| to_timestamp | Converts a string to a `Timestamp(_, _)` |
+| to_timestamp_millis | Converts a string to a `Timestamp(Milliseconds, None)` |
+| to_timestamp_micros | Converts a string to a `Timestamp(Microseconds, None)` |
+| to_timestamp_seconds | Converts a string to a `Timestamp(Seconds, None)` |
+| now() | Returns current time. |
## Other Expressions
-| Function | Notes |
-| -------- | ----- |
-| array | |
-| in_list | |
-| random | |
-| sha224 | |
-| sha256 | |
-| sha384 | |
-| sha512 | |
-| struct | |
-| to_hex | |
+| Function | Notes |
+| ---------------------------- | ---------------------------------------------------------------------------------------------------------- |
+| array([value1, ...]) | Returns an array of fixed size with each argument (`[value1, ...]`) on it. |
+| in_list(expr, list, negated) | Returns `true` if (`expr`) belongs or not belongs (`negated`) to a list (`list`), otherwise returns false. |
+| random() | Returns a random value from 0 (inclusive) to 1 (exclusive). |
+| sha224(text) | Computes the SHA224 hash of the argument (`text`). |
+| sha256(text) | Computes the SHA256 hash of the argument (`text`). |
+| sha384(text) | Computes the SHA384 hash of the argument (`text`). |
+| sha512(text) | Computes the SHA512 hash of the argument (`text`). |
+| struct | |
Review Comment:
```sql
❯ select struct('soo');
+---------------------+
| struct(Utf8("soo")) |
+---------------------+
| {c0: soo} |
+---------------------+
```
Wow that is a wild funtion 🤔
##########
docs/source/user-guide/expressions.md:
##########
@@ -125,105 +135,105 @@ Unlike to some databases the math functions in Datafusion works the same way as
## String Expressions
-| Function | Notes |
-| ---------------- | ----- |
-| ascii | |
-| bit_length | |
-| btrim | |
-| char_length | |
-| character_length | |
-| concat | |
-| concat_ws | |
-| chr | |
-| initcap | |
-| left | |
-| length | |
-| lower | |
-| lpad | |
-| ltrim | |
-| md5 | |
-| octet_length | |
-| repeat | |
-| replace | |
-| reverse | |
-| right | |
-| rpad | |
-| rtrim | |
-| digest | |
-| split_part | |
-| starts_with | |
-| strpos | |
-| substr | |
-| translate | |
-| trim | |
-| upper | |
+| Function | Notes |
+| ---------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| ascii(character) | Returns a numeric representation of the character (`character`). Example: `ascii('a') -> 97` |
Review Comment:
At least some of these functions are already covered in https://arrow.apache.org/datafusion/user-guide/sql/scalar_functions.html#string-functions
However, I see this is for the expression syntax. 🤔
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