postgresql
Design a PostgreSQL-specific schema. Covers best-practices, data types, indexing, constraints, performance patterns, and advanced features
name:postgresqldescription:Design a PostgreSQL-specific schema. Covers best-practices, data types, indexing, constraints, performance patterns, and advanced features
PostgreSQL Table Design
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Instructions
EXPLAIN.Safety
Core Rules
BIGINT GENERATED ALWAYS AS IDENTITY; use UUID only when global uniqueness/opacity is needed.NUMERIC for exact decimal arithmetic).PostgreSQL “Gotchas”
snake_case for table/column names.UNIQUE (...) NULLS NOT DISTINCT (PG15+) to restrict to one NULL.NUMERIC(2,0) fails with error, unlike some databases that silently truncate or round.CLUSTER is one-off reorganization, not maintained on subsequent inserts. Row order on disk is insertion order unless explicitly clustered.Data Types
BIGINT GENERATED ALWAYS AS IDENTITY preferred (GENERATED BY DEFAULT also fine); UUID when merging/federating/used in a distributed system or for opaque IDs. Generate with uuidv7() (preferred if using PG18+) or gen_random_uuid() (if using an older PG version).BIGINT unless storage space is critical; INTEGER for smaller ranges; avoid SMALLINT unless constrained.DOUBLE PRECISION over REAL unless storage space is critical. Use NUMERIC for exact decimal arithmetic.TEXT; if length limits needed, use CHECK (LENGTH(col) <= n) instead of VARCHAR(n); avoid CHAR(n). Use BYTEA for binary data. Large strings/binary (>2KB default threshold) automatically stored in TOAST with compression. TOAST storage: PLAIN (no TOAST), EXTENDED (compress + out-of-line), EXTERNAL (out-of-line, no compress), MAIN (compress, keep in-line if possible). Default EXTENDED usually optimal. Control with ALTER TABLE tbl ALTER COLUMN col SET STORAGE strategy and ALTER TABLE tbl SET (toast_tuple_target = 4096) for threshold. Case-insensitive: for locale/accent handling use non-deterministic collations; for plain ASCII use expression indexes on LOWER(col) (preferred unless column needs case-insensitive PK/FK/UNIQUE) or CITEXT.NUMERIC(p,s) (never float).TIMESTAMPTZ for timestamps; DATE for date-only; INTERVAL for durations. Avoid TIMESTAMP (without timezone). Use now() for transaction start time, clock_timestamp() for current wall-clock time.BOOLEAN with NOT NULL constraint unless tri-state values are required.CREATE TYPE ... AS ENUM for small, stable sets (e.g. US states, days of week). For business-logic-driven and evolving values (e.g. order statuses) → use TEXT (or INT) + CHECK or lookup table.TEXT[], INTEGER[], etc. Use for ordered lists where you query elements. Index with GIN for containment (@>, <@) and overlap (&&) queries. Access: arr[1] (1-indexed), arr[1:3] (slicing). Good for tags, categories; avoid for relations—use junction tables instead. Literal syntax: '{val1,val2}' or ARRAY[val1,val2].daterange, numrange, tstzrange for intervals. Support overlap (&&), containment (@>), operators. Index with GiST. Good for scheduling, versioning, numeric ranges. Pick a bounds scheme and use it consistently; prefer [) (inclusive/exclusive) by default.INET for IP addresses, CIDR for network ranges, MACADDR for MAC addresses. Support network operators (<<, >>, &&).POINT, LINE, POLYGON, CIRCLE for 2D spatial data. Index with GiST. Consider PostGIS for advanced spatial features.TSVECTOR for full-text search documents, TSQUERY for search queries. Index tsvector with GIN. Always specify language: to_tsvector('english', col) and to_tsquery('english', 'query'). Never use single-argument versions. This applies to both index expressions and queries.CREATE DOMAIN email AS TEXT CHECK (VALUE ~ '^[^@]+@[^@]+$') for reusable custom types with validation. Enforces constraints across tables.CREATE TYPE address AS (street TEXT, city TEXT, zip TEXT) for structured data within columns. Access with (col).field syntax.vector type by pgvector for vector similarity search for embeddings.Do not use the following data types
timestamp (without time zone); DO use timestamptz instead.char(n) or varchar(n); DO use text instead.money type; DO use numeric instead.timetz type; DO use timestamptz instead.timestamptz(0) or any other precision specification; DO use timestamptz insteadserial type; DO use generated always as identity instead.Table Types
Row-Level Security
Enable with ALTER TABLE tbl ENABLE ROW LEVEL SECURITY. Create policies: CREATE POLICY user_access ON orders FOR SELECT TO app_users USING (user_id = current_user_id()). Built-in user-based access control at the row level.
Constraints
ON DELETE/UPDATE action (CASCADE, RESTRICT, SET NULL, SET DEFAULT). Add explicit index on referencing column—speeds up joins and prevents locking issues on parent deletes/updates. Use DEFERRABLE INITIALLY DEFERRED for circular FK dependencies checked at transaction end.NULLS NOT DISTINCT (PG15+). Standard behavior: (1, NULL) and (1, NULL) are allowed. With NULLS NOT DISTINCT: only one (1, NULL) allowed. Prefer NULLS NOT DISTINCT unless you specifically need duplicate NULLs.CHECK (price > 0) allows NULL prices. Combine with NOT NULL to enforce: price NUMERIC NOT NULL CHECK (price > 0).EXCLUDE USING gist (room_id WITH =, booking_period WITH &&) prevents double-booking rooms. Requires appropriate index type (often GiST).Indexing
=, <, >, BETWEEN, ORDER BY)WHERE a = ? AND b > ? uses index on (a,b), but WHERE b = ? does not). Put most selective/frequently filtered columns first.CREATE INDEX ON tbl (id) INCLUDE (name, email) - includes non-key columns for index-only scans without visiting table.WHERE status = 'active' → CREATE INDEX ON tbl (user_id) WHERE status = 'active'). Any query with status = 'active' can use this index.CREATE INDEX ON tbl (LOWER(email))). Expression must match exactly in WHERE clause: WHERE LOWER(email) = 'user@example.com'.@>, ?), full-text search (@@)CLUSTER).Partitioning
PARTITION BY RANGE (created_at)). Create partitions: CREATE TABLE logs_2024_01 PARTITION OF logs FOR VALUES FROM ('2024-01-01') TO ('2024-02-01'). TimescaleDB automates time-based or ID-based partitioning with retention policies and compression.PARTITION BY LIST (region)). Example: FOR VALUES IN ('us-east', 'us-west').PARTITION BY HASH (user_id)). Creates N partitions with modulus.CHECK constraints on partitions for query planner to prune. Auto-created for declarative partitioning (PG10+).Special Considerations
Update-Heavy Tables
fillfactor=90 to leave space for HOT updates that avoid index maintenance.Insert-Heavy Workloads
COPY or multi-row INSERT instead of single-row inserts.BIGINT GENERATED ALWAYS AS IDENTITY over UUID.Upsert-Friendly Design
ON CONFLICT (col1, col2) needs exact matching unique index (partial indexes don't work).EXCLUDED.column to reference would-be-inserted values; only update columns that actually changed to reduce write overhead.DO NOTHING faster than DO UPDATE when no actual update needed.Safe Schema Evolution
BEGIN; ALTER TABLE...; ROLLBACK; for safe testing.CREATE INDEX CONCURRENTLY avoids blocking writes but can't run in transactions.NOT NULL columns with volatile defaults (e.g., now(), gen_random_uuid()) rewrites entire table. Non-volatile defaults are fast.ALTER TABLE DROP CONSTRAINT then DROP COLUMN to avoid dependency issues.CREATE OR REPLACE with different arguments creates overloads, not replacements. DROP old version if no overload desired.Generated Columns
... GENERATED ALWAYS AS () STORED for computed, indexable fields. PG18+ adds VIRTUAL columns (computed on read, not stored).Extensions
pgcrypto: crypt() for password hashing.uuid-ossp: alternative UUID functions; prefer pgcrypto for new projects.pg_trgm: fuzzy text search with % operator, similarity() function. Index with GIN for LIKE '%pattern%' acceleration.citext: case-insensitive text type. Prefer expression indexes on LOWER(col) unless you need case-insensitive constraints.btree_gin/btree_gist: enable mixed-type indexes (e.g., GIN index on both JSONB and text columns).hstore: key-value pairs; mostly superseded by JSONB but useful for simple string mappings.timescaledb: essential for time-series—automated partitioning, retention, compression, continuous aggregates.postgis: comprehensive geospatial support beyond basic geometric types—essential for location-based applications.pgvector: vector similarity search for embeddings.pgaudit: audit logging for all database activity.JSONB Guidance
JSONB with GIN index.CREATE INDEX ON tbl USING GIN (jsonb_col); → accelerates:- Containment
jsonb_col @> '{"k":"v"}'- Key existence
jsonb_col ? 'k', any/all keys ?\|, ?&- Path containment on nested docs
- Disjunction
jsonb_col @> ANY(ARRAY['{"status":"active"}', '{"status":"pending"}'])@> workloads: consider opclass jsonb_path_ops for smaller/faster containment-only indexes:-
CREATE INDEX ON tbl USING GIN (jsonb_col jsonb_path_ops);- Trade-off: loses support for key existence (
?, ?|, ?&) queries—only supports containment (@>)-
ALTER TABLE tbl ADD COLUMN price INT GENERATED ALWAYS AS ((jsonb_col->>'price')::INT) STORED;-
CREATE INDEX ON tbl (price);- Prefer queries like
WHERE price BETWEEN 100 AND 500 (uses B-tree) over WHERE (jsonb_col->>'price')::INT BETWEEN 100 AND 500 without index.@> for containment (e.g., tags). Consider jsonb_path_ops if only doing containment.config JSONB NOT NULL CHECK(jsonb_typeof(config) = 'object')Examples
Users
CREATE TABLE users (
user_id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
email TEXT NOT NULL UNIQUE,
name TEXT NOT NULL,
created_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
CREATE UNIQUE INDEX ON users (LOWER(email));
CREATE INDEX ON users (created_at);Orders
CREATE TABLE orders (
order_id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
user_id BIGINT NOT NULL REFERENCES users(user_id),
status TEXT NOT NULL DEFAULT 'PENDING' CHECK (status IN ('PENDING','PAID','CANCELED')),
total NUMERIC(10,2) NOT NULL CHECK (total > 0),
created_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
CREATE INDEX ON orders (user_id);
CREATE INDEX ON orders (created_at);JSONB
CREATE TABLE profiles (
user_id BIGINT PRIMARY KEY REFERENCES users(user_id),
attrs JSONB NOT NULL DEFAULT '{}',
theme TEXT GENERATED ALWAYS AS (attrs->>'theme') STORED
);
CREATE INDEX profiles_attrs_gin ON profiles USING GIN (attrs);