Temporary functions allow users to define functions that are session-specific and used to encapsulate reusable logic within a database session. While both PL/SQL and Spark SQL support the concept of user-defined functions, their implementation and usage differ significantly.

Temporary Functions in PL/SQL

PL/SQL, primarily used with Oracle databases, allows you to create temporary or anonymous functions within a block of code. These functions are often used to perform specific tasks within a session and are not stored in the database schema permanently.

Example: Temporary Function in PL/SQL

Here’s an example of how to create and use a temporary function within a PL/SQL block:

DECLARE
    -- Define a local function
    FUNCTION concatenate(first_name IN VARCHAR2, last_name IN VARCHAR2) RETURN VARCHAR2 IS
    BEGIN
        RETURN first_name || '-' || last_name;
    END concatenate;

BEGIN
    -- Use the local function
    DBMS_OUTPUT.PUT_LINE(concatenate('Alice', 'Smith'));
    DBMS_OUTPUT.PUT_LINE(concatenate('Bob', 'Johnson'));
END;
/

In this example:

• A temporary function concatenate is defined within a PL/SQL block.
• This function concatenates two strings with a hyphen.
• The function is used within the same block to print concatenated names.

Temporary Functions in Spark SQL

Spark SQL does not support defining temporary functions directly within SQL code as PL/SQL does. Instead, Spark SQL uses user-defined functions (UDFs) registered through the Spark API (e.g., in Python or Scala). These UDFs can be registered for the duration of a Spark session and used within SQL queries.

Example: Temporary Function in Spark SQL (Python)

Here’s how you define and use a UDF in Spark SQL:

from pyspark.sql import SparkSession
from pyspark.sql.functions import udf
from pyspark.sql.types import StringType

# Initialize Spark session
spark = SparkSession.builder.appName("Temporary Functions").getOrCreate()

# Sample data
data = [
    ("Alice", "Smith"),
    ("Bob", "Johnson"),
    ("Charlie", "Williams")
]

columns = ["first_name", "last_name"]

# Create DataFrame
df = spark.createDataFrame(data, columns)

# Register the DataFrame as a temporary view
df.createOrReplaceTempView("people")

# Define the UDF
def concatenate(first, last):
    return f"{first}-{last}"

# Register the UDF as a temporary function
spark.udf.register("concatenate", concatenate, StringType())

# Use the temporary function in a Spark SQL query
result_df = spark.sql("""
SELECT first_name, last_name, concatenate(first_name, last_name) AS full_name
FROM people
""")

# Show the result
result_df.show()

In this example:

• A Spark session is initialized, and a sample DataFrame is created and registered as a temporary view.
• A UDF concatenate is defined in Python to concatenate two strings with a hyphen.
• The UDF is registered with the Spark session and can be used as a temporary function in SQL queries.

Comparison

Defining Temporary Functions

• PL/SQL:
  • Functions can be defined directly within a PL/SQL block.
  • Functions are local to the block and not stored permanently.
• Spark SQL:
  • Functions (UDFs) are defined using the Spark API (e.g., in Python, Scala).
  • UDFs must be registered with the Spark session to be used in SQL queries.
  • Functions are session-specific but not directly written in SQL.

Usage Scope

• PL/SQL:
  • Temporary functions are used within the scope of the PL/SQL block in which they are defined.
• Spark SQL:
  • UDFs are registered for the Spark session and can be used across multiple SQL queries within that session.

Language and Flexibility

• PL/SQL:
  • Functions are written in PL/SQL, which is closely integrated with Oracle databases.
  • Provides strong support for procedural logic.
• Spark SQL:
  • UDFs can be written in various languages supported by Spark (e.g., Python, Scala).
  • Provides flexibility to use different programming languages and integrate complex logic from external libraries.

While both PL/SQL and Spark SQL support the concept of temporary or session-specific functions, their implementation and usage differ. PL/SQL allows for the direct definition of temporary functions within blocks of code, providing a tightly integrated procedural approach. In contrast, Spark SQL relies on user-defined functions (UDFs) registered through the Spark API, offering flexibility and language diversity but requiring an additional step to register and use these functions in SQL queries.