Most of the major RDBMSs that support JSON also include a json_valid() function for checking the validity of a JSON document, and DuckDB’s no exception. Like the other RDBMSs, DuckDB’s implementation of json_valid() checks its argument and returns a boolean value to indicate whether or not it’s valid JSON.
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3 DuckDB Functions that Prepend a Value to a List
DuckDB provides us with a few functions that prepend a value to a list. Actually, these functions are synonymous, so they all do the same thing, with the same/similar basic syntax.
Using LIST_INTERSECT() to Extract Overlapping Elements from Two Lists in DuckDB
The list_intersect() can be quite a handy function when working with lists in DuckDB. It accepts two lists as arguments, and it returns a list of elements that are common to both lists. It essentially performs a set intersection operation while preserving the list data type.
Duplicate values are ignored, so only one value is returned even if there are multiple occurrences in one or both lists.
An Important Consideration When Choosing Between LIST_CONCAT() and || For Concatenating Lists in DuckDB
When it comes to concatenating lists in DuckDB, we can use the list_concat() function (and its aliases), or the list concatenation operator (||). Often when we have a choice like this, we can use either option interchangeably. But that isn’t quite true in this case.
There’s an important difference between list_concat() and the || operator in DuckDB, and it all comes down to how it handles NULL values.
A Quick Look at DuckDB’s JSON_VALUE() Function
DuckDB provides a handful of functions for getting data from JSON documents. We can use them as long as the JSON extension is installed and loaded (which it is in most distributions). One such function for getting data from a JSON document is json_value(). This function extracts scalar data from the specified path in the JSON document. If the value isn’t scalar, then a NULL value is returned.
Understanding JSON_EXTRACT_STRING() in DuckDB
DuckDB has a json_extract_string() function that works similar to json_extract(), except that it returns its result as a string (varchar). The json_extract() function, on the other hand, returns its result as JSON.
The purpose of these two functions is to extract data from a JSON document. We’ll focus on the json_extract_string() function in this article.
Using JSON_EXTRACT() in DuckDB
DuckDB has a json_extract() function that extracts JSON data from a JSON document. It enables us to get JSON values from within the JSON document, rather than returning the whole document itself. This article takes a quick look at the function along with some examples of usage.
Examples of EPOCH_US() in DuckDB
DuckDB provides us with a bunch of epoch...() functions that enable us to get the Unix epoch time from a given date/time value. Different functions return their result using different units (for example seconds, milliseconds, etc). The epoch_us() function returns its result in microseconds.
Unix epoch time is typically expressed as the number of seconds that have elapsed since January 1, 1970 (UTC), but epoch_us() function returns the equivalent amount in microseconds.
DuckDB JSON_EXISTS(): Check if a Path Exists in a JSON Document
Most DuckDB distributions are shipped with the json extension, which enables us to work with JSON documents. DuckDB provides a bunch of JSON functions, including JSON_EXISTS(). The JSON_EXISTS() function allows us to check whether a specific path exists within a JSON document.
This article explores how this function works, along with examples.
A Quick Look at EPOCH_MS() in DuckDB
In DuckDB, the epoch_ms() function serves a dual purpose. It converts timestamp values into Unix epoch time in milliseconds and also performs the reverse operation, transforming Unix epoch time values back into timestamps.
Unix epoch time is typically expressed as the number of seconds that have elapsed since January 1, 1970 (UTC), but this function returns the equivalent amount in milliseconds.
The function is similar to the epoch() function, which returns its result in seconds. However, the epoch() function only works in one direction; it converts a timestamp value to epoch time, but it doesn’t work the other way around like epoch_ms() can.