When working with DuckDB, we may need to determine whether a specific value exists within a list or array. Fortunately, DuckDB offers four synonymous functions that enable us to accomplish this.
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Unnesting Lists & Structs with DuckDB’s UNNEST() Function
DuckDB has an unnest() function that we can use to unnest lists and structs. Well, it can also be applied to NULL, but that’ll return an empty result.
By “unnest” I mean it takes the list or struct, and it returns its contents as rows in a table. You might say that it converts lists and structs into tables, where each item in the list or struct becomes a row in the table.
Below are examples of using DuckDB’s unnest() function to unnest lists and structs.
Fix ‘Binder Error: ‘list_has_all’ cannot compare lists of different types’ in DuckDB
If you’re getting an error that reads “Binder Error: ‘list_has_all’ cannot compare lists of different types” in DuckDB, it appears that you’re passing two different types of lists to the list_has_all() function.
DuckDB’s list_has_all() function accepts two lists as arguments. These need to be of the same type.
To fix this issue, make sure that both lists are of the same type.
Add Months to a Date in DuckDB
DuckDB provides us with an easy way to add one or more months to date values, as well as subtract from them. This applies to the various date related data types, such as DATE and TIMESTAMP.
Actually, DuckDB provides us with a choice; We can use the + operator or the date_add() function.
Fix “Sample method … cannot be used with a discrete sample count” When Using the SAMPLE Clause in DuckDB
If you’re getting an error that reads something like “Sample method System cannot be used with a discrete sample count” when using the SAMPLE clause in DuckDB, it looks like you’re specifying an invalid sampling method for the context with which you’re using the SAMPLE clause. Perhaps you’re using system or bernoulli, when you should be using reservoir.
Check if a Sub-List Appears in a Larger List in DuckDB: LIST_HAS_ALL()
When working with lists in DuckDB, we sometimes need to check whether a list contains specific elements. The list_has_all() function is a handy tool that allows us to verify if all elements of one list exist within another. This function is particularly useful in filtering queries, data validation, and advanced list-based operations.
In this article, we’ll explore how list_has_all() works in DuckDB.
Fix ‘Binder Error: Could not find key “…” in struct’ When Using DuckDB’s ARRAY_EXTRACT() Function
If you’re getting an error that reads something like “Binder Error: Could not find key “…” in struct” when using the array_extract() function in DuckDB, it could be that you’re specifying a non-existent key.
When using DuckDB’s array_extract() function to extract a value from a struct, we must provide a key that actually exists in the struct. Otherwise we’ll end up with an error like the above one.
To fix this issue, be sure to specify a key that actually exists in the struct.
Flattening Nested Lists with DuckDB’s FLATTEN() Function
DuckDB has a flatten() function that we can use to flatten nested lists. The function concatenates a list of lists into a single list. So whether the outer list contains just one list or multiple lists, we can use the flatten() function to flatten them into one list.
However, it only goes one level deep, so that’s something to keep in mind.
How to Get the Abbreviated Day Name in DuckDB
When working with DuckDB, sometimes we might need to get the weekday name from a date or timestamp value. And sometimes we might want just the abbreviated weekday name, rather than the full name. For example, we might want Mon instead of Monday.
Fix “Could not convert string ‘…’ to INT64” When Using the GENERATE_SUBSCRIPTS() Function in DuckDB
If you’re getting an error that reads something like “Could not convert string ‘…’ to INT64” when using the generate_subscripts() function in DuckDB, it appears that your second argument is a string, when it should be an integer.
DuckDB’s generate_subscripts() function accepts two arguments; the array as the first argument, and the dimension as the second argument. The second argument must be INT64 (or be able to be implicitly converted to that type). Passing the wrong data type as the second argument can cause the above error to occur.
To fix this issue, make sure that the second argument is compatible with INT64.