SQL Best Practices

SQL isn’t just about data. It’s about performance, readability, and stability. Bad queries scale poorly. Small mistakes can slow entire systems. This guide shows how to write SQL that’s easy to maintain and hard to break.

SQL Schema Design Best Practices

A strong schema is your most significant source of performance gain.

• normalize to remove duplicates, but stop before joins explode
• Use clear names for tables and columns
• pick proper data types (int, decimal, datetime2, not nvarchar(max))
• always set primary and foreign keys
• define unique and check constraints
• Add indexes carefully

Example:

create table orders (
    id bigint primary key,
    user_id bigint not null references users(id),
    total decimal(10,2) not null check (total >= 0),
    created_at datetime2 default sysdatetime()
)

💡 Tip: design around how data will be queried, not just how it’s stored.

SQL Query Style Best Practices

• avoid select *
• Use consistent aliasing and indentation
• comment complex logic
• Keep joins readable and grouped
• Use a clear filter order

SQL Performance and Optimization Best Practices

• Check the execution plan before fixing anything
• Use indexes that match your where and join
• Don’t wrap indexed columns in functions
• Use cte instead of nested subqueries
• Batch inserts and updates
• Use pagination for large selects

💡 Tip: set statistics io, time on shows you what’s really happening.

SQL Transactions and Concurrency Best Practices

• Wrap related operations in one transaction
• keep it short
• know your isolation levels (read committed, serializable, etc.)
• handle deadlocks and retries
• avoid full-table locks

💡 tip: One long transaction can block the whole system.

SQL Security Best Practices

• Never concatenate strings in SQL
• always use parameters
• apply least privilege
• encrypt sensitive columns
• audit access and schema changes

💡Tip: The database should never trust user input directly.

SQL Maintenance and Versioning

• Keep all scripts in git
• automate migrations (flyway, liquibase, ef migrations)
• document schema updates
• Monitor slow queries regularly
• archive old or inactive data

💡 Tip: your DBA is not your backup strategy.

SQL Common Anti-patterns

• using distinct to “fix” bad joins
• Adding too many indexes
• ignoring null handling
• using nvarchar(max) for everything
• relying blindly on ORM-generated SQL
• nested views on views

Checklist

• schema normalized and constrained
• naming clear and consistent
• no select *
• indexes verified
• short transactions
• parameters everywhere
• migrations automated
• monitoring enabled