Postgresql

PL/pgSQL Programming

• Creating stored functions and procedures
• Writing triggers
• Implementing complex business logic in the database
• Performance optimization through server-side computation

Administration

• Installing and configuring PostgreSQL
• Running regression tests
• Managing users, roles, and permissions
• Backup and recovery operations
• Understanding Write-Ahead Logging (WAL)

Key Concepts

ACID Properties

PostgreSQL is fully ACID-compliant:

• Atomicity: Transactions are all-or-nothing operations
• Consistency: Database moves from one valid state to another
• Isolation: Concurrent transactions don't see each other's incomplete changes
• Durability: Committed transactions survive system failures via WAL

Write-Ahead Logging (WAL)

Changes are logged before being applied to data files. This enables:

• Crash recovery without data loss
• Point-in-time recovery
• Online backup and replication
• Reduced disk I/O (sequential log writes vs. random data page writes)

PL/pgSQL Advantages

Server-side procedural language that:

• Eliminates client/server round trips
• Avoids transferring intermediate results
• Reduces query parsing overhead
• Can use all SQL data types and functions

Quick Reference

Creating Tables

Basic table creation (from official docs):

CREATE TABLE my_first_table (
    first_column text,
    second_column integer
);

Table with foreign key constraint (from official docs):

CREATE TABLE cities (
    name     varchar(80) PRIMARY KEY,
    location point
);

CREATE TABLE weather (
    city      varchar(80) REFERENCES cities(name),
    temp_lo   int,
    temp_hi   int,
    prcp      real,
    date      date
);

Table inheritance (from official docs):

CREATE TABLE cities (
    name       text,
    population real,
    elevation  int     -- (in ft)
);

CREATE TABLE capitals (
    state      char(2) UNIQUE NOT NULL
) INHERITS (cities);

Querying Data

Basic SELECT (from official docs):

SELECT * FROM weather;

SELECT city, temp_lo, temp_hi, prcp, date FROM weather;

Computed columns with aliases (from official docs):

SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather;

JOIN operations (from official docs):

-- Inner join
SELECT * FROM weather JOIN cities ON city = name;

-- Explicit column selection with qualified names
SELECT weather.city, weather.temp_lo, weather.temp_hi,
       weather.prcp, weather.date, cities.location
    FROM weather JOIN cities ON weather.city = cities.name;

Creating Views

Encapsulate complex queries (from official docs):

CREATE VIEW myview AS
    SELECT name, temp_lo, temp_hi, prcp, date, location
        FROM weather, cities
        WHERE city = name;

SELECT * FROM myview;

Creating Indexes

Basic index creation (from official docs):

CREATE TABLE test1 (
    id integer,
    content varchar
);

CREATE INDEX test1_id_index ON test1 (id);

Modifying Data

UPDATE statement (from official docs):

UPDATE weather
    SET temp_hi = temp_hi - 2,  temp_lo = temp_lo - 2
    WHERE date > '1994-11-28';

INSERT statement (from official docs):

INSERT INTO weather VALUES ('Berkeley', 45, 53, 0.0, '1994-11-28');

Transactions

Basic transaction block (from official docs):

BEGIN;
UPDATE accounts SET balance = balance - 100.00
    WHERE name = 'Alice';
-- ... more operations ...
COMMIT;

Using savepoints (from official docs):

BEGIN;
UPDATE accounts SET balance = balance - 100.00
    WHERE name = 'Alice';
SAVEPOINT my_savepoint;
UPDATE accounts SET balance = balance + 100.00
    WHERE name = 'Bob';
-- oops ... forget that and use Wally's account
ROLLBACK TO my_savepoint;
UPDATE accounts SET balance = balance + 100.00
    WHERE name = 'Wally';
COMMIT;

Embedded SQL (ECPG)

Prepared statements in C (from official docs):

EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "INSERT INTO test1 VALUES(?, ?);";
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE mystmt FROM :stmt;
EXEC SQL EXECUTE mystmt USING 42, 'foobar';

Database Administration

Creating a database (from official docs):

$ createdb mydb

Removing a database (from official docs):

$ dropdb mydb

Setting up shared libraries (from official docs):

LD_LIBRARY_PATH=/usr/local/pgsql/lib
export LD_LIBRARY_PATH

Running Tests

Parallel regression tests (from official docs):

make check        # Against temporary installation
make installcheck # Against running server
make check-world  # All test suites

Reference Files

This skill includes comprehensive documentation in references/:

getting_started.md

Source: Official PostgreSQL 18 Documentation Confidence: Medium Pages: 46 Content:

• Installation requirements and procedures
• Creating databases and connecting
• SQL tutorial (tables, queries, joins)
• Transactions and savepoints
• Views, foreign keys, inheritance
• Running regression tests

sql.md

Source: Official PostgreSQL 18 Documentation Confidence: Medium Pages: 1088 Content:

• Complete SQL command reference
• PL/pgSQL procedural language
• User-defined functions and procedures
• Security labels and permissions
• Dynamic SQL with ECPG
• Information schema details

index.md

Source: Official PostgreSQL 18 Documentation Confidence: Medium Content:

• Documentation category index
• Navigation guide to reference files

Working with This Skill

For Beginners

1. Start with references/getting_started.md for installation and basic SQL
2. Follow the tutorial sections (Chapter 2: SQL Language, Chapter 3: Advanced Features)
3. Practice with the weather/cities example tables from the docs
4. Learn transaction basics with BEGIN/COMMIT/ROLLBACK

For Intermediate Users

1. Explore references/sql.md for complete SQL command syntax
2. Study PL/pgSQL for server-side programming (Section 41)
3. Learn about indexes and query optimization (Chapter 11)
4. Understand views and foreign keys for better schema design

For Advanced Users

1. Deep dive into PL/pgSQL for complex stored procedures
2. Study Write-Ahead Logging for understanding durability
3. Explore embedded SQL (ECPG) for C applications
4. Reference the information schema for metadata queries

Navigation Tips

• Use section numbers (e.g., "31.1", "41.1") to locate specific topics
• The URL patterns follow PostgreSQL docs structure (e.g., /docs/18/tutorial-select.html)
• Code examples are language-tagged for proper syntax highlighting
• Look for "Examples:" sections for practical code samples

Common Patterns

Pattern: Referential Integrity with Foreign Keys

Ensure data consistency by declaring foreign key constraints:

CREATE TABLE orders (
    order_id    serial PRIMARY KEY,
    customer_id integer REFERENCES customers(id),
    order_date  date
);

Pattern: Safe Updates with Transactions

Wrap related changes in a transaction block:

BEGIN;
-- Multiple related operations
UPDATE inventory SET quantity = quantity - 1 WHERE product_id = 123;
INSERT INTO order_items (order_id, product_id) VALUES (456, 123);
COMMIT;

Pattern: Query Encapsulation with Views

Hide complexity behind a view interface:

CREATE VIEW active_customers AS
    SELECT c.*, COUNT(o.order_id) as order_count
    FROM customers c
    LEFT JOIN orders o ON c.id = o.customer_id
    WHERE c.status = 'active'
    GROUP BY c.id;

Pattern: Performance with Indexes

Create indexes on frequently queried columns:

CREATE INDEX idx_orders_customer ON orders(customer_id);
CREATE INDEX idx_orders_date ON orders(order_date);

Error Handling

Foreign Key Violation

ERROR:  insert or update on table "weather" violates foreign key constraint
DETAIL:  Key (city)=(Berkeley) is not present in table "cities".

Solution: Insert the referenced row first, or use ON DELETE/UPDATE actions.

Transaction Aborted

After an error in a transaction, you must either:

• ROLLBACK to abort and start fresh
• ROLLBACK TO savepoint to return to a known good state

Resources

references/

Organized documentation extracted from official PostgreSQL sources:

• Detailed explanations with context
• Code examples with language annotations
• Links to original documentation URLs
• Hierarchical table of contents

scripts/

Add helper scripts for common automation tasks:

• Database migration scripts
• Backup and restore procedures
• Performance testing utilities

assets/

Add templates and examples:

• Schema templates
• Sample data files
• Configuration examples

Notes

• This skill was generated from PostgreSQL 18 official documentation
• Reference files preserve original structure and examples
• Code examples include language tags for syntax highlighting
• Examples prioritize practical, real-world patterns from official docs
• PL/pgSQL is installed by default since PostgreSQL 9.0

Updating

To refresh this skill with updated documentation:

1. Re-run the scraper with the PostgreSQL configuration
2. The skill will be rebuilt with the latest information
3. Check for new features in major version releases

Source Information

Primary Source: PostgreSQL 18 Official Documentation Documentation URL: https://www.postgresql.org/docs/18/ Source Confidence: Medium (official documentation) Last Updated: Generated from current documentation