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.

Example of Error

Here’s an example of code that produces the error:

SELECT array_extract(
    { 'name' : 'Fetch', 'type' : 'Dog' },
    'Oops'
);

Result:

Binder Error: Could not find key "oops" in struct

Candidate Entries: "type"

Here, I passed a key called Oops, but there’s no such key in the struct.

Sometimes this error could be due to us inadvertently passing a value instead of a key. For example:

SELECT array_extract(
    { 'name' : 'Fetch', 'type' : 'Dog' },
    'Fetch'
);

Result:

Binder Error: Could not find key "fetch" in struct

Candidate Entries: "name"

Same error, although this time it suggested a different “candidate entry”. Regardless, the solution is the same.

Solution

To fix this issue, we need to specify a key that actually exists in the struct.

Example:

SELECT array_extract(
    { 'name' : 'Fetch', 'type' : 'Dog' },
    'name'
);

Result:

Fetch

This time it worked. I specified the name key, and the function returned the value at that key.