In PostgreSQL, we can use array constructors to create arrays that contain elements that we specify. We can populate the array from literal values, or we can let a query provide the values.
We can also create multi-dimensional arrays. When populating the array from a query, we can use multiple subqueries to create each sub-array. Therefore we can create a multi-dimensional array from a query.
Continue readingIn PostgreSQL, the regexp_split_to_array() function splits a string using a POSIX regular expression as the delimiter, and returns the result in a text array.
So we use a POSIX regular expression to specify the delimiter/s, and split the string based on that.
We pass the string as the first argument and the pattern as the second. We can also specify a flag to determine how the function behaves.
Continue readingIn PostgreSQL, the regexp_split_to_table() function splits a string using a POSIX regular expression as the delimiter, and returns the result in a table.
So we use a POSIX regular expression to specify the delimiter/s, and split the string based on that.
We pass the string as the first argument and the pattern as the second. We can also specify a flag to change the behaviour of the function.
Continue readingWhen 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 readingIf you’re getting an error that reads “ERROR: cannot take logarithm of a negative number” when using either the log() function or log10() function in PostgreSQL, it’s probably because you’re passing a negative value to the function.
These functions require a value greater than zero. This is true even for the base argument of the log() function (the argument that specifies which base to use).
To fix this issue, be sure to pass a value greater than zero to these functions.
Continue readingIn PostgreSQL, an array constructor is an expression that builds an array value using values for its member elements.
One of the things we can do is build an array based on the results of a subquery.
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.
If you’re getting an error that reads something like ‘time zone “US/New_York” not recognized‘ in PostgreSQL while using a function such as date_add(), date_subtract() or date_trunc(), it’s probably because you’re specifying an unsupported time zone.
If you specify a time zone, it must be one that’s recognised by the system.
To fix this issue, either provide a recognised time zone or omit the time zone argument altogether (assuming this is a valid option for the situation).
Continue readingIn 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.
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