postgresql_pl_pgsql — consolidated language guide — DedSec Project

PostgreSQL PL/pgSQL

Typical use: Databases and data languages.

Suggested file extension: .sql.

How to run / environment: Run in a PostgreSQL database with privileges to create functions.

Starter example

CREATE OR REPLACE FUNCTION greet(name text)
RETURNS text LANGUAGE plpgsql AS $
BEGIN
  RETURN 'Hello, ' || name || '!';
END; $;
SELECT greet('Ada');

How to read it

Use parameterized application queries and migrations.

Common pitfall

Use parameterized application queries and migrations.

PostgreSQL_PL_pgSQL — Expanded practice workbook

Start with actual syntax

The archive's starter gives a minimal valid entry point for PostgreSQL PL pgSQL. Read its operators, declarations and output mechanism; then verify it with the correct interpreter rather than treating another language's syntax as interchangeable.

CREATE OR REPLACE FUNCTION greet(name text)
RETURNS text LANGUAGE plpgsql AS $
BEGIN
  RETURN 'Hello, ' || name || '!';
END; $;
SELECT greet('Ada');

Run context: Run in a PostgreSQL database with privileges to create functions.. Before editing, check the exact compiler or interpreter version and save its output. Keep this exercise in a scratch directory, not inside a production project.

Guided laboratory

Create safe_double(n integer) with BEGIN/END and a $ body, reject negatives with RAISE EXCEPTION and test NULL and overflow as separate contracts.

Boundary-case investigation

A one-dollar function delimiter is malformed; use proper dollar quoting. Keep side effects and transaction locks visible during testing.

Extended assignment

Starting from the exact sample, implement the guided lab in a separate file, then attempt one change involving ordering, shape, type, scope or environment as appropriate to PostgreSQL PL pgSQL. Explain your invariant and compare expected versus actual output in a small table. Preserve a minimal reproducer for any unexpected behavior; only then expand the example.

PostgreSQL PL pgSQL — Technical notes and common pitfalls

Core knowledge

1. PL/pgSQL adds procedural control flow around SQL operations.
2. Use parameterized queries from clients and protect dynamic SQL identifiers through validated allow-lists.
3. Understand exception handling and transaction scope of the caller before modifying stored routines.