PostgreSQL fails on empty constructor arrays

When working with PostgreSQL, you might encounter an error stating "cannot determine type of empty array" when querying with an empty constructor array. This error occurs because PostgreSQL requires explicit type casting for empty arrays to properly interpret their data type. To resolve this issue and successfully execute your query, follow these steps:

Explicitly Cast Empty Arrays:

To explicitly cast an empty array to a specific data type, use the following syntax:

select array[]::data_type;

For example, to cast an empty array to an integer array, use:

select array[]::integer[];

Determine Array Type with Type Information:

To determine the data type of an array without explicitly casting it, you can use the information_schema.columns view. This view provides detailed information about columns, including their data types.

To retrieve the data type of an array column, use the following query:

select column_name, data_type from information_schema.columns where table_name = 'table_name' and column_name = 'array_column_name';

Replace table_name with the name of your table and array_column_name with the name of your array column.

Use ARRAY[] Constructor:

Another way to create an empty array of a specific data type is to use the ARRAY[] constructor. This method is similar to explicit casting, but it doesn't require you to specify the data type explicitly.

To create an empty integer array using the ARRAY[] constructor:

select ARRAY[];

Note: The ARRAY[] constructor is supported in PostgreSQL versions 9.0 and later.

Additional Information:

• PostgreSQL's handling of empty arrays aims to prevent data type ambiguity and ensure data integrity.
• Explicit casting allows you to specify the desired data type explicitly, resolving the ambiguity and enabling successful query execution.
• The information_schema.columns view provides valuable information about columns, including their data types, which can be useful for determining the data type of an array column.
• The ARRAY[] constructor is a convenient way to create empty arrays of a specific data type, but it's only supported in PostgreSQL versions 9.0 and later.

By following these steps and understanding the underlying concepts, you can effectively handle empty constructor arrays in PostgreSQL and avoid the "cannot determine type of empty array" error.