In PostgreSQL, there is a data type called “pseudo type” which is not an actual data type but can be used as a placeholder for other types. Pseudo types provide flexibility and convenience in certain scenarios where we don’t want to specify a specific data type.
What are Pseudo Types?
Pseudo types are special data types in PostgreSQL that do not have a physical representation. They cannot be used to declare columns in tables or variables in PL/pgSQL functions. Instead, they serve as placeholders or containers for other data types.
Common Pseudo Types
PostgreSQL provides several built-in pseudo types that can be used in various situations:
- anyelement: This pseudo type represents any single data type, including composite types and domains.
- anyarray: It represents an array of any element type.
- anyenum: It represents any enumerated (enum) type.
- anynonarray: This pseudo type represents any non-array data type.
- anyrange: It represents any range data type.
Usage of Pseudo Types
Pseudo types are mainly used when we want to write functions or procedures that can accept multiple input data types. By using pseudo types, we can create generic functions that work with different kinds of input without specifying the exact data type.
To illustrate the usage of pseudo types, let’s consider an example of a function called “find_max”. This function takes an array of integers as input and returns the maximum value from that array:
“`sql
CREATE FUNCTION find_max(arr anyarray) RETURNS anyelement AS $$
DECLARE
max_value anyelement;
BEGIN
SELECT INTO max_value MAX(value) FROM unnest(arr) AS value;
RETURN max_value;
END;
$$ LANGUAGE plpgsql;
“`
In the above example, the parameter “arr” is of type “anyarray”, which means it can accept arrays of any data type. Inside the function, we use the pseudo type “anyelement” to declare the variable “max_value”. This allows us to handle different data types dynamically.
Conclusion
Pseudo types in PostgreSQL provide a convenient way to handle multiple data types within functions and procedures. They allow us to create flexible and generic code that can work with different input data without explicitly specifying the data type. By utilizing pseudo types, we can enhance the reusability and versatility of our database code.
So, next time you need to write a function that can accept various data types, consider using pseudo types in PostgreSQL!