When using PostgreSQL, we can use the starts_with() function to check whether or not a string starts with a given substring.
We pass the string as the first argument, and the substring as the second.
It returns true if the string does start with the substring, otherwise it returns false.
Continue readingPostgreSQL has the SOME() construct that we can use to perform searches against arrays. It returns a Boolean result, and so we can incorporate this into our searches to return just those rows that yield true or false.
SOME() is a synonym for ANY(), and so we can use either one to get the same result.
In PostgreSQL, log10() is a mathematical function that returns the base 10 logarithm of its argument.
It was added in PostgreSQL 12 as a SQL-standard equivalent of the existing log() function.
There is a difference between the two functions though, because log() allows us to specify which base to use (although it defaults to base 10), whereas log10() uses base 10 only.
In PostgreSQL, we can use the trim_scale() function to remove any trailing zeros from the end of the fractional part.
This doesn’t change the value, it merely reduces the number characters whenever there are unnecessary zeros on the end.
Continue readingIn PostgreSQL, min_scale() is a mathematical function that returns the minimum scale needed to represent the supplied value precisely.
The “scale” is the number of fractional decimal digits. For example, a value of 1.9500 has a minimum scale of 2, whereas 1.957 has a minimum scale of 3.
We pass the value to the function as a numeric argument, and it returns the result as an integer.
PostgreSQL has an extensive collection of built-in string functions that allow us to manipulate text values. One task we might want to perform is to extract a substring from a larger string. Fortunately, PostgreSQL caters for our needs with at least two functions that make this a breeze.
Continue readingIn PostgreSQL, we can use the reverse() function to return a specified string with its characters reversed. In other words, the string is returned with its characters in the reverse order to how we provided them.
In PostgreSQL, the regexp_matches() function returns substrings that match a given POSIX regular expression in a given string. We can specify that all matches are returned or just the first match. If all matches are returned, each is returned in a separate row.
We pass the string as the first argument and the pattern as the second argument. We can also provide a flag as an optional third argument, which determines how the function behaves.
Each returned row is a text array containing the whole matched substring or the substrings matching parenthesised subexpressions of the pattern.
Continue readingIn PostgreSQL, the regexp_match() function returns a text array containing substrings that match a given POSIX regular expression in a given string. Only the first match is returned (to return all matches, use regexp_matches() instead).
We pass the string as the first argument and the pattern as the second argument. We can also provide a flag as an optional third argument, which determines how the function behaves.
Continue readingPostgreSQL has a pg_input_error_info() function that allows us to see the error details that would be returned if we were to pass an invalid value for the specified data type.
Basically it tests whether the given string is valid input for the specified data type. If invalid, it returns the details of the error that would have been thrown. If valid, the result is null.