mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-10-22 08:20:48 +00:00
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
80 lines
3.2 KiB
Markdown
80 lines
3.2 KiB
Markdown
# Functions for searching and replacing in strings
|
|
|
|
## replaceOne(haystack, pattern, replacement)
|
|
|
|
Replaces the first occurrence, if it exists, of the 'pattern' substring in 'haystack' with the 'replacement' substring.
|
|
Hereafter, 'pattern' and 'replacement' must be constants.
|
|
|
|
## replaceAll(haystack, pattern, replacement)
|
|
|
|
Replaces all occurrences of the 'pattern' substring in 'haystack' with the 'replacement' substring.
|
|
|
|
## replaceRegexpOne(haystack, pattern, replacement)
|
|
|
|
Replacement using the 'pattern' regular expression. A re2 regular expression.
|
|
Replaces only the first occurrence, if it exists.
|
|
A pattern can be specified as 'replacement'. This pattern can include substitutions `\0-\9`.
|
|
The substitution `\0` includes the entire regular expression. Substitutions `\1-\9` correspond to the subpattern numbers.To use the `\` character in a template, escape it using `\`.
|
|
Also keep in mind that a string literal requires an extra escape.
|
|
|
|
Example 1. Converting the date to American format:
|
|
|
|
```sql
|
|
SELECT DISTINCT
|
|
EventDate,
|
|
replaceRegexpOne(toString(EventDate), '(\\d{4})-(\\d{2})-(\\d{2})', '\\2/\\3/\\1') AS res
|
|
FROM test.hits
|
|
LIMIT 7
|
|
FORMAT TabSeparated
|
|
```
|
|
|
|
```text
|
|
2014-03-17 03/17/2014
|
|
2014-03-18 03/18/2014
|
|
2014-03-19 03/19/2014
|
|
2014-03-20 03/20/2014
|
|
2014-03-21 03/21/2014
|
|
2014-03-22 03/22/2014
|
|
2014-03-23 03/23/2014
|
|
```
|
|
|
|
Example 2. Copying a string ten times:
|
|
|
|
```sql
|
|
SELECT replaceRegexpOne('Hello, World!', '.*', '\\0\\0\\0\\0\\0\\0\\0\\0\\0\\0') AS res
|
|
```
|
|
|
|
```text
|
|
┌─res────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
|
|
│ Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World!Hello, World! │
|
|
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
|
|
```
|
|
|
|
## replaceRegexpAll(haystack, pattern, replacement)
|
|
|
|
This does the same thing, but replaces all the occurrences. Example:
|
|
|
|
```sql
|
|
SELECT replaceRegexpAll('Hello, World!', '.', '\\0\\0') AS res
|
|
```
|
|
|
|
```text
|
|
┌─res────────────────────────┐
|
|
│ HHeelllloo,, WWoorrlldd!! │
|
|
└────────────────────────────┘
|
|
```
|
|
|
|
As an exception, if a regular expression worked on an empty substring, the replacement is not made more than once.
|
|
Example:
|
|
|
|
```sql
|
|
SELECT replaceRegexpAll('Hello, World!', '^', 'here: ') AS res
|
|
```
|
|
|
|
```text
|
|
┌─res─────────────────┐
|
|
│ here: Hello, World! │
|
|
└─────────────────────┘
|
|
```
|
|
|