Contents
- 1 What kind of pattern matching does PostgreSQL use?
- 2 Can you select a different escape character in PostgreSQL?
- 3 Which is the modern form of a PostgreSQL re?
- 4 What do the flags mean in PostgreSQL regular expressions?
- 5 What does the flags parameter do in PostgreSQL?
- 6 Which is the escape double quote separator in PostgreSQL?
What kind of pattern matching does PostgreSQL use?
There are three separate approaches to pattern matching provided by PostgreSQL: the traditional SQL LIKE operator, the more recent SIMILAR TO operator (added in SQL:1999), and POSIX -style regular expressions.
Can you select a different escape character in PostgreSQL?
You can avoid this by selecting a different escape character with ESCAPE; then a backslash is not special to LIKE anymore. (But it is still special to the string literal parser, so you still need two of them.) It’s also possible to select no escape character by writing ESCAPE ”.
How to match underscore without matching other characters?
To match a literal underscore or percent sign without matching other characters, the respective character in pattern must be preceded by the escape character. The default escape character is the backslash but a different one can be selected by using the ESCAPE clause. To match the escape character itself, write two escape characters.
When does a string match a regular expression?
A string is said to match a regular expression if it is a member of the regular set described by the regular expression. As with LIKE, pattern characters match string characters exactly unless they are special characters in the regular expression language — but regular expressions use different special characters than LIKE does.
Which is the modern form of a PostgreSQL re?
PostgreSQL implements the modern form. A (modern) RE is one or more non-empty branches, separated by |. It matches anything that matches one of the branches. A branch is one or more pieces , concatenated. It matches a match for the first, followed by a match for the second, etc.
What do the flags mean in PostgreSQL regular expressions?
Flag i specifies case-insensitive matching, while flag g specifies replacement of each matching substring rather than only the first one. PostgreSQL ‘s regular expressions are implemented using a package written by Henry Spencer.
What does the regexp _ replace function do in PostgreSQL?
The regexp_replace function provides substitution of new text for substrings that match POSIX regular expression patterns. It has the syntax regexp_replace (source, pattern, replacement flags ]). The source string is returned unchanged if there is no match to the pattern.
How are the first and third regular expressions used in PostgreSQL?
(In POSIX parlance, the first and third regular expressions are forced to be non-greedy.) As an extension to the SQL standard, PostgreSQL allows there to be just one escape-double-quote separator, in which case the third regular expression is taken as empty; or no separators, in which case the first and third regular expressions are taken as empty.
What does the flags parameter do in PostgreSQL?
The flags parameter is an optional text string containing zero or more single-letter flags that change the function’s behavior. Flag g causes the function to find each match in the string, not only the first one]
Which is the escape double quote separator in PostgreSQL?
As an extension to the SQL standard, PostgreSQL allows there to be just one escape-double-quote separator, in which case the third regular expression is taken as empty; or no separators, in which case the first and third regular expressions are taken as empty. Some examples, with #” delimiting the return string: