postgresql-server-programming

PostgreSQL Server Programming

Use When

• PostgreSQL server-side programming sourced from "PostgreSQL Server Programming" (Usama Dar, Packt) and "Introduction to PostgreSQL for the Data Professional". Covers PL/pgSQL functions and procedures (structure, variables, error handling, loops, cursors), trigger functions (row-level, statement-level, WHEN conditions), event triggers (DDL auditing), extensions (creating and publishing), and best practices (SOA, DRY, KISS). Companion to postgresql-fundamentals and postgresql-advanced-sql.
• The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.

Do Not Use When

• The task is unrelated to postgresql-server-programming or would be better handled by a more specific companion skill.
• The request only needs a trivial answer and none of this skill's constraints or references materially help.

Required Inputs

• Gather relevant project context, constraints, and the concrete problem to solve; load references only as needed.
• Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.

Workflow

• Read this SKILL.md first, then load only the referenced deep-dive files that are necessary for the task.
• Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
• Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.

Quality Standards

• Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
• Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
• Prefer deterministic, reviewable steps over vague advice or tool-specific magic.

Anti-Patterns

• Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
• Loading every reference file by default instead of using progressive disclosure.

Outputs

• A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
• Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
• References used, companion skills, or follow-up actions when they materially improve execution.

Evidence Produced

Category	Artifact	Format	Example
Correctness	Server-side function test plan	Markdown doc covering PL/pgSQL function tests, trigger tests, and extension behaviour	docs/data/postgres-server-tests.md

References

• Use the references/ directory for deep detail after reading the core workflow below.

Why Program in the Server

• Data locality — avoid network round trips for complex logic
• Integrity enforcement — triggers fire regardless of which client writes
• Security — grant EXECUTE on functions, deny direct table access
• Performance — reduce per-row round trips in batch operations
• Auditability — triggers capture changes transparently

Use server-side code for integrity, auditing, and data-local transformation. Keep business logic that requires application context in the application layer.

PL/pgSQL Function Structure

CREATE OR REPLACE FUNCTION function_name(param1 type, param2 type)
RETURNS return_type
LANGUAGE plpgsql
AS $$
DECLARE
    var1  data_type := initial_value;
    var2  data_type;
    rec   RECORD;
BEGIN
    -- body
    RETURN result;
END;
$$;

Volatility Categories

Category	Description	Optimiser Benefit
IMMUTABLE	Same input always gives same output, no DB access	Most aggressive inlining
STABLE	Same input gives same output within a transaction	Safe for index scans
VOLATILE (default)	Can return different results or modify data	No optimisation

-- Immutable: pure computation
CREATE FUNCTION slugify(text) RETURNS text LANGUAGE sql IMMUTABLE AS $$
    SELECT lower(regexp_replace(regexp_replace($1, '[^a-zA-Z0-9\s-]', '', 'g'), '\s+', '-', 'g'));
$$;

-- Stable: reads DB but doesn't modify it
CREATE FUNCTION get_exchange_rate(currency text) RETURNS numeric LANGUAGE sql STABLE AS $$
    SELECT rate FROM exchange_rates WHERE code = currency;
$$;

Additional Guidance

Extended guidance for postgresql-server-programming was moved to references/skill-deep-dive.md to keep this entrypoint compact and fast to load.

Use that deep dive for:

• Variables and Data Types
• Control Flow
• Error Handling
• Returning Structured Data
• Stored Procedures
• Trigger Functions
• Event Triggers (DDL Auditing)
• Cursors
• Extensions
• Programming Best Practices
• Anti-Patterns