[H1][CODING-PG]

Dictum: PostgreSQL schema design, query algebra, and security posture govern all SQL work.

All SQL follows five governing principles:

• Polymorphic — one function/query per concern, generic over specific via parameter dispatch and dynamic SQL
• Set-algebraic — express operations as set transformations; zero row-at-a-time iteration
• Strongly typed — domain types, composite types, range types; zero untyped text columns for structured data
• Programmatic — variable-driven predicates, parameterized DDL, zero stringly-typed identifiers
• Declarative-first — constraints, generated columns, and RLS policies enforce invariants at the schema level; application logic is last resort
• Source-current — PostgreSQL 18/current docs are the truth baseline; examples must state current semantics, not stale point-version folklore

Paradigm

• Immutability: append-only event tables, temporal versioning via tstzrange + WITHOUT OVERLAPS, soft-delete via archived_at timestamp — zero in-place mutation of historical records
• Type anchoring: one CREATE TYPE or CREATE DOMAIN per semantic concept — derive column declarations from domain types, never redeclare equivalent CHECK constraints across tables
• Expression control flow: CASE-free query design via COALESCE, NULLIF, GREATEST/LEAST, lateral joins, and FILTER (WHERE ...) — reserve CASE for irreducible multi-branch projection only
• Set composition: CTEs as named relational algebra steps; UNION ALL over procedural accumulation; MERGE over conditional INSERT/UPDATE sequences
• Constraint-driven integrity: CHECK, EXCLUDE, WITHOUT OVERLAPS, GENERATED ALWAYS AS — push validation into DDL; application-layer checks are redundant defense, not primary enforcement
• Extension-first: pgvector for embeddings, pg_trgm for fuzzy search, PostGIS for spatial, TimescaleDB for time-series — never hand-roll what an extension provides

Conventions

Layer	Mechanism	Owns
Identity	uuidv7()	PK generation — timestamp-ordered, B-tree friendly
Temporal	WITHOUT OVERLAPS + PERIOD	Range integrity — temporal PKs, FKs, exclusion constraints
Projection	Virtual generated columns	Computed fields — zero storage, instant ALTER TABLE
Write strategy	MERGE ... RETURNING OLD/NEW	Upsert + audit trail in single statement
Type safety	Domain types + composite types	Semantic column typing — branded scalars, structured records
Search	GIN + pg_trgm / pgvector	Full-text, trigram similarity, vector nearest-neighbor
Partitioning	Declarative + pg_partman	Time/hash/list partitioning with automatic lifecycle
Scheduling	pg_cron	In-database job scheduling — maintenance, materialized views
Security	RLS + SECURITY INVOKER	Row-level tenant isolation, least-privilege function execution
Observability	pg_stat_statements + auto_explain	Query fingerprinting, automatic slow-query plan capture

• Effect-SQL (@effect/sql + @effect/sql-pg) is the assumed TypeScript integration layer.
• Model.Class field modifiers (Generated, FieldOnly, FieldExcept, Sensitive) must align with DDL constraints — Generated fields map to DEFAULT or GENERATED ALWAYS AS columns.
• All SQL identifiers use snake_case; TypeScript receives camelCase via transformResultNames.

Contracts

Type discipline

• One domain type per semantic concept; column declarations reference the domain, never inline CHECK constraints.
• Composite types for structured return values from functions — never OUT parameter proliferation.
• Range types (tstzrange, int4range, custom) for interval semantics — never dual start/end columns.
• NOT NULL is default posture; nullable columns require documented justification.

Query algebra

• CTEs for named intermediate results; recursive CTEs with SEARCH BREADTH FIRST or CYCLE for graph traversal.
• MERGE with RETURNING OLD.*, NEW.*, merge_action() for write-audit fusion.
• Window functions with GROUPS/EXCLUDE framing where row-count framing is insufficient.
• JSON_TABLE / jsonb_path_query for structured JSON extraction — never application-side JSON parsing of database-resident JSON.
• LATERAL JOIN for correlated subquery materialization — never scalar subqueries in SELECT list.

Index strategy

• Every WHERE clause pattern has a corresponding index; partial indexes for selective predicates.
• INCLUDE columns for index-only scans on high-frequency read paths.
• GIN for JSONB containment (@>), array overlap (&&), full-text (@@).
• GiST for range overlap, spatial queries, nearest-neighbor when combined with ORDER BY <-> LIMIT.
• BRIN for append-only monotonic columns (timestamps, serial IDs) — orders of magnitude smaller than B-tree.

Security

• RLS enabled on every tenant-scoped table; policies use fail-closed nullif(current_setting('app.current_tenant', true), '') tenant scoping.
• Functions default to SECURITY INVOKER (always the default); SECURITY DEFINER only with SET search_path = pg_catalog, public.
• Column-level GRANT for sensitive fields — never rely on view-based column hiding alone.

Performance

• EXPLAIN (ANALYZE, BUFFERS, VERBOSE, SETTINGS) is the verification tool; assertions against plan shape, not just row counts.
• AIO (io_method = io_uring) for sequential scan and vacuum workloads on Linux.
• Parallel query enabled for aggregation, hash join, index scan — max_parallel_workers_per_gather tuned to workload.
• FOR UPDATE SKIP LOCKED for concurrent batch processing — never SELECT ... FOR UPDATE without SKIP LOCKED on queue tables.

Anti-Patterns

Label	Symptom
STRING_TYPING	text for structured data (JSON, enum values, composite structures)
DUAL_COLUMN_RANGE	start_date/end_date instead of tstzrange with exclusion constraint
IMPERATIVE_BATCH	PL/pgSQL LOOP with row-at-a-time UPDATE instead of set-based MERGE/CTE
INDEX_SPRAWL	Redundant single-column indexes subsumed by existing composite indexes
NULLABLE_DEFAULT	Columns nullable without documented justification
TRIGGER_LOGIC	Business logic in triggers instead of MERGE RETURNING or generated columns
OFFSET_PAGINATION	LIMIT/OFFSET instead of keyset pagination for client-facing endpoints
SECURITY_DEFINER_LEAK	SECURITY DEFINER without SET search_path — search_path injection vector
STRINGLY_POLICY	RLS policy with hardcoded literals instead of current_setting()
FUNCTION_PROLIFERATION	Separate functions for each query variant instead of one polymorphic function
APPLICATION_SIDE_JSON	Fetching raw JSONB and parsing in application instead of jsonb_path_query
MANUAL_PARTITION	Hand-written partition creation instead of pg_partman lifecycle management
UNVALIDATED_CONSTRAINT	ADD CONSTRAINT ... NOT VALID without subsequent VALIDATE CONSTRAINT
IF_THEN_DISPATCH	PL/pgSQL IF p_op = 'get' THEN ... ELSIF instead of VALUES-based dynamic SQL
NONCOMPOSABLE_CAGG	PERCENTILE_CONT in hierarchical CAGG; non-composable across tiers
LEGACY_UUID	Non-ordered UUID generation on new ordered PKs where uuidv7() fits better
STALE_HEALTH_VIEW	Materialized views for real-time health monitoring instead of inline queries
EXCLUDE_OVER_WITHOUT_OVERLAPS	EXCLUDE instead of WITHOUT OVERLAPS PK/UNIQUE for temporal overlap in PG 18
RAW_UUID_ID	Raw S.UUID for PK/FK instead of S.UUID.pipe(S.brand('EntityId'))
BARE_FOR_UPDATE	FOR UPDATE without SKIP LOCKED on batch/queue processing patterns
NULL_UNSAFE_ANTIJOIN	NOT IN (SELECT ...) instead of NOT EXISTS; NULL in subquery yields UNKNOWN
DISTINCT_OVER_EXISTS	SELECT DISTINCT on joined data; use EXISTS semi-join (avoids sort/dedup)

Load Sequence

Foundation (always load):

• references/validation.md — compliance checklist, Effect-SQL alignment, migration safety

Task-routed references (load when the task matches):

• references/ddl.md — schema design, domain/composite/range types, temporal constraints, generated columns, partitioning, lock levels
• references/queries.md — CTE algebra, MERGE, window functions, JSON_TABLE, recursive patterns
• references/indexes.md — index type selection, partial indexes, covering indexes, maintenance
• references/functions.md — polymorphic functions, custom aggregates, procedures, PL/pgSQL dispatch
• references/extensions.md — load when: pgvector, pg_trgm, PostGIS, TimescaleDB, pg_cron, pg_partman, pg_duckdb, embeddings, similarity search, time-series, spatial, partitioning automation, analytics, OLAP, analytical
• references/security.md — load when: RLS, row-level security, tenant isolation, privileges, audit, pgaudit
• references/observability.md — load when: monitoring, statistics, auto_explain, wait events, lock contention
• references/performance.md — load when: tuning, io_uring, JIT, parallel query, vacuum, SSD, NVMe, EXPLAIN
• references/replication.md — load when: replication, publications, subscriptions, conflict tracking, CDC

First-Class Extensions

Extension	Owns	Load When
pgvector	Vector storage, HNSW/IVFFlat/DiskANN indexes	Embedding search, similarity queries
pgvectorscale	DiskANN index, Statistical Binary Quantization	>1M vectors, memory-constrained
pg_search	BM25 full-text via Tantivy, @@@ operator	Search-quality ranking, hybrid search
pg_trgm	Trigram similarity, GIN trigram indexes, % operator	Fuzzy text search, typo tolerance
PostGIS	Geometry/geography types, spatial indexes, ST_* funcs	Geospatial queries, proximity search
TimescaleDB	Hypertables, continuous aggregates, compression	Time-series ingestion, rollup queries
pg_cron	In-database scheduled jobs	Materialized view refresh, maintenance
pg_partman	Partition lifecycle management	Non-time-series partitioning
pg_duckdb	Embedded DuckDB, analytical acceleration, lake access	OLAP queries, Parquet/Iceberg reads
pg_jsonschema	JSONB validation via JSON Schema CHECK constraints	Structured JSONB columns
btree_gist	GiST equality operators for EXCLUDE constraints	Range + equality exclusion constraints
bloom	Bloom filter index for wide-table equality	>5 columns, arbitrary WHERE combos
pg_stat_statements	Query fingerprinting, execution statistics	Performance analysis, regression detect
pgaudit	Compliance-grade audit logging (session + object)	SOC 2, HIPAA, PCI-DSS compliance

Validation Gate

After writing or modifying SQL, run in order:

1. Automated lint: bash scripts/pg_lint.sh [PATH...] from this skill directory — anti-pattern detectors (rg-based + structural). Errors (E) block merge; warnings (W) require justification. Supports --json, --sql-only, --ts-only, and --self-test.
2. Manual checklist: references/validation.md — compliance gates not automatable (Effect-SQL alignment, migration safety, lock-level awareness).