The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

SQL Workflow

Tool Grid

Naming Conventions

Tables and Columns

• All identifiers MUST use snake_case
• Table names SHOULD be plural nouns (e.g., users, order_items)
• Column names MUST be descriptive and unambiguous
• Primary keys SHOULD be named id or {table_singular}_id
• Foreign keys MUST follow {referenced_table_singular}_id pattern
• Boolean columns SHOULD use is_, has_, or can_ prefix

Examples

-- Good
CREATE TABLE orders (
    id BIGINT PRIMARY KEY,
    user_id BIGINT NOT NULL,
    is_completed BOOLEAN DEFAULT FALSE,
    created_at TIMESTAMP WITH TIME ZONE
);

-- Bad
CREATE TABLE Order (
    OrderID INT,
    userId INT,
    completed BOOLEAN
);

Data Types

Preferred Types

• Text: MUST use TEXT over VARCHAR unless length constraint is business requirement
• Timestamps: MUST use TIMESTAMP WITH TIME ZONE for all temporal data
• Integers: SHOULD use BIGINT for IDs to prevent overflow
• Decimals: MUST use NUMERIC(precision, scale) for money/financial data
• UUIDs: SHOULD use native UUID type when available
• JSON: SHOULD use JSONB over JSON for PostgreSQL

Avoid

• CHAR(n) - wastes space with padding
• FLOAT/DOUBLE for financial calculations
• TIMESTAMP without time zone

Migrations

File Naming

Migrations MUST follow: YYYYMMDD_HHMMSS_description.sql

20241215_143022_create_users_table.sql
20241215_150000_add_email_index_to_users.sql
20241216_090000_create_orders_table.sql

Migration Structure

-- Migration: 20241215_143022_create_users_table.sql
-- Description: Creates the users table with core fields

BEGIN;

CREATE TABLE users (
    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    email TEXT NOT NULL,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
);

COMMIT;

Rules

• Each migration MUST be wrapped in a transaction (BEGIN/COMMIT)
• Migrations MUST be idempotent when possible (use IF NOT EXISTS)
• Down migrations SHOULD be provided for reversible changes
• Data migrations MUST be separate from schema migrations

Query Style

Formatting

• Keywords MUST be uppercase: SELECT, FROM, WHERE, JOIN
• Identifiers MUST be lowercase: users, created_at
• Each major clause SHOULD start on a new line
• Indentation SHOULD be 4 spaces
• Commas SHOULD be at the end of lines (trailing commas)

Example

SELECT
    u.id,
    u.email,
    COUNT(o.id) AS order_count
FROM users AS u
LEFT JOIN orders AS o
    ON u.id = o.user_id
WHERE u.is_active = TRUE
    AND u.created_at >= '2024-01-01'
GROUP BY u.id, u.email
HAVING COUNT(o.id) > 0
ORDER BY order_count DESC
LIMIT 100;

Aliases

• Table aliases MUST be meaningful (not single letters for complex queries)
• Column aliases MUST use AS keyword explicitly
• Aliases SHOULD be lowercase

Indexes

When to Create

• Primary keys automatically create indexes
• Foreign key columns SHOULD have indexes
• Columns frequently used in WHERE clauses SHOULD be indexed
• Columns used in ORDER BY with LIMIT SHOULD be considered
• Composite indexes for multi-column queries

Naming Convention

idx_{table}_{column(s)}
idx_{table}_{column1}_{column2}

Examples

-- Single column index
CREATE INDEX idx_users_email ON users (email);

-- Composite index
CREATE INDEX idx_orders_user_id_created_at ON orders (user_id, created_at);

-- Partial index
CREATE INDEX idx_orders_pending ON orders (id)
WHERE status = 'pending';

-- Unique index
CREATE UNIQUE INDEX idx_users_email_unique ON users (email);

Anti-patterns

• Indexes on low-cardinality columns (boolean, status with few values)
• Too many indexes on write-heavy tables
• Unused indexes consuming storage

Constraints

Foreign Keys

ALTER TABLE orders
ADD CONSTRAINT fk_orders_user_id
FOREIGN KEY (user_id) REFERENCES users (id)
ON DELETE CASCADE
ON UPDATE CASCADE;

Check Constraints

ALTER TABLE products
ADD CONSTRAINT chk_products_price_positive
CHECK (price > 0);

ALTER TABLE users
ADD CONSTRAINT chk_users_email_format
CHECK (email ~* '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$');

Naming

• Foreign keys: fk_{table}_{column}
• Check constraints: chk_{table}_{description}
• Unique constraints: uq_{table}_{column(s)}

NULL Handling

Rules

• MUST use IS NULL / IS NOT NULL for NULL comparisons
• MUST NOT use = NULL or != NULL
• SHOULD use COALESCE() for default values
• SHOULD use NULLIF() to convert values to NULL

Examples

-- Correct NULL handling
SELECT * FROM users WHERE deleted_at IS NULL;

-- Using COALESCE for defaults
SELECT COALESCE(nickname, email) AS display_name FROM users;

-- Using NULLIF to handle empty strings
SELECT NULLIF(phone, '') AS phone FROM users;

Performance

Query Analysis

• MUST use EXPLAIN ANALYZE before optimizing
• SHOULD check for sequential scans on large tables
• SHOULD monitor query execution time

EXPLAIN ANALYZE
SELECT * FROM orders WHERE user_id = 123;

Best Practices

• MUST NOT use SELECT * in production code
• SHOULD specify only required columns
• SHOULD use EXISTS instead of COUNT(*) for existence checks
• SHOULD use LIMIT with ORDER BY for pagination
• MUST avoid N+1 queries - use JOINs or batch fetching

Examples

-- Bad: SELECT *
SELECT * FROM users WHERE id = 1;

-- Good: Explicit columns
SELECT id, email, created_at FROM users WHERE id = 1;

-- Bad: COUNT for existence
SELECT COUNT(*) > 0 FROM orders WHERE user_id = 1;

-- Good: EXISTS
SELECT EXISTS (SELECT 1 FROM orders WHERE user_id = 1);

Transactions

Rules

• Write operations SHOULD use explicit transactions
• Transactions MUST be as short as possible
• SHOULD set appropriate isolation level when needed

Example

BEGIN;

UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;

COMMIT;

Isolation Levels

-- For critical financial operations
BEGIN ISOLATION LEVEL SERIALIZABLE;
-- ... operations ...
COMMIT;

SQLFluff Configuration

Recommended .sqlfluff

[sqlfluff]
dialect = postgres
templater = raw
max_line_length = 120

[sqlfluff:rules:capitalisation.keywords]
capitalisation_policy = upper

[sqlfluff:rules:capitalisation.identifiers]
capitalisation_policy = lower

[sqlfluff:rules:layout.long_lines]
ignore_comment_lines = True

Common Pitfalls