add postgresql functions concept

[hakdo99]

Description

Add a concept entry about PostgreSQL functions. The new file is functions.md.

Issue Solved

Closes #4589

Type of Change

• Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[SaviDahegaonkar]

Hey @hakdo99 ,
The entry is nicely written, and I have suggested a few changes. Please make them asap.

Thanks,
Savi

[SaviDahegaonkar]

Suggested change

	- 'learn-postgresql'
	- 'learn-postgresql'

Include only those course paths that are already available in the catalog-content.md file. You can add one if you want it to get included in the PR. Here learn-postgresql is not available in the catalog-content file so it makes it invalid to get included in PR.

[SaviDahegaonkar]

Hey @NelsonSanti ,
Can I know if you have implemented the suggested changes so I can make it available for a second review?

[NelsonSanti]

Hello @SaviDahegaonkar
it seems you were mistaken,
This job is not assigned to me.
No worries and thank you!

[SaviDahegaonkar]

Hello @SaviDahegaonkar it seems you were mistaken, This job is not assigned to me. No worries and thank you!

Yeah, I am really sorry for the misunderstanding.

[SaviDahegaonkar]

Hey @hakdo99 ,
Can I know if you have implemented the suggested changes so I can make it available for a second review?

Thanks,
Savi

[SaviDahegaonkar]

Hey @hakdo99 ,
LGTM! Thank You for Contributing to docs :)

Thanks,
Savi

[SaviDahegaonkar]

Suggested change

	```pseudo
	CREATE [OR REPLACE] FUNCTION function_name(parameters)
	RETURNS return_type AS $$
	DECLARE
	<variable_name> <data_type>;
	BEGIN
	<function_logic>;
	RETURN <value_or_variable>;
	END;
	$$ LANGUAGE lang_name;
	```pseudo
	CREATE [OR REPLACE] FUNCTION function_name(parameters)
	RETURNS return_type AS $$
	DECLARE
	<variable_name> <data_type>;
	BEGIN
	<function_logic>;
	RETURN <value_or_variable>;
	END;
	$$ LANGUAGE lang_name;

[github-actions]

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