How to return result of a SELECT inside a function in PostgreSQL?

sql

sql-functions

postgresql

best-practices

byAnton Shumikhin·Nov 11, 2024

To efficiently return the output of a SELECT query from a PostgreSQL function, use RETURNS TABLE:

CREATE FUNCTION fetch_data() 
RETURNS TABLE(id INT, name TEXT) AS $$
BEGIN
    RETURN QUERY SELECT id, name FROM my_table; -- Send the main course to the customer! 😄
END;
$$ LANGUAGE plpgsql;

You can call this function using the following syntax:

SELECT * FROM fetch_data(); -- Here comes your tasty data! 🍽️

Inside the function kitchen

Let's dive deeper into the world of SQL functions and excel your skillset with some professional tips:

Don't play hide and seek with OUT parameters

Select descriptive and unique names for your OUT parameters to avoid any name conflicts.

RETURNS TABLE(employee_id INT, product_name TEXT)  -- No more guessing games!

Say no to troublemaker data types

Don't use names like 'text' or 'count' for your columns. They can cross swords with PostgreSQL internal types and lead to unexpected conflicts!

Mastermind arithmetic expressions

Integer division can play tricky sometimes — always multiply before you divide to reduce rounding errors and achieve precise results.

Meet the superheroes: Window functions & CTEs

To handle complex queries, don't shy away from using window functions or common table expressions (CTEs). They're your best friends to simplify and optimize your code.

Rounding? Do it right!

Employ the round() function with two parameters when rounding numeric values. This ensures that your results are precise and accurate to the desired decimal points.

Test, rinse, repeat!

Don't forget to test your function thorough using a SELECT statement to ensure it returns the expected results.

Use fully qualified names

When referencing columns, especially in complex queries involving multiple tables, use fully qualified names to prevent any unexpected conflicts.

Going the extra mile with functions

Leverage window functions and CTEs

Window functions and CTEs are powerful tools to handle complex SQL logic. They help break down your logic into smaller, more manageable pieces for enhanced readability and optimization.

Precise rounding? Yes, please!

Utilize round(column_name, precision) to control the rounding of numeric values precisely. Avoid losing crucial decimals and maintain the accuracy of your results.

Test your functions like a boss

Reiterate through real-world scenarios when applying your function. Duplicate a production-like test environment, apply your function on a subset of your data and ensure everything works as expected.

Exploring the function journey

Speaking the function language

Leverage LANGUAGE SQL in your function declaration to denote that your function's logic is written in standard SQL.

Function syntax gone stylish!

Applying AS $functionname$ syntax enhances the readability of your function definition. Consider this a major style upgrade for your PostgreSQL functions.

Specify your function's return gifts

RETURNS TABLE is not just a statement, it's a promise. Ensure you deliver the right data structure by explicitly specifying the column names and data types.

RETURNS TABLE(id INT, name TEXT) -- And the winning type is...

Enroll for PostgreSQL university

Nothing beats the official PostgreSQL documentation. They say wisdom comes from learning, so do frequent the official PostgreSQL documentation for comprehensive understanding and examples.

explain-codes / Sql / How to return result of a SELECT inside a function in PostgreSQL?

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