Follow these SQL best practices to write maintainable, efficient, and secure queries.

Formatting and Readability

-- Use consistent capitalization

SELECT

customer_name,

order_date,

total_amount

FROM orders

WHERE status = 'completed'

ORDER BY order_date DESC;

Use Meaningful Aliases

SELECT

c.name AS customer_name,

COUNT(o.id) AS order_count

FROM customers c

LEFT JOIN orders o ON c.id = o.customer_id

GROUP BY c.id;

Always Use WHERE with UPDATE/DELETE

-- Always include WHERE to avoid disasters

UPDATE products SET price = 99.99 WHERE id = 123;

DELETE FROM logs WHERE created_at < '2024-01-01';

Use Parameterized Queries

-- Prevent SQL injection

-- Bad: "SELECT * FROM users WHERE id = " + userId

-- Good: "SELECT * FROM users WHERE id = ?"

Comment Complex Logic

-- Calculate customer lifetime value

-- Includes only completed orders from last 2 years

SELECT customer_id, SUM(total) as ltv

FROM orders

WHERE status = 'completed'

AND order_date > DATE_SUB(NOW(), INTERVAL 2 YEAR)

GROUP BY customer_id;

Avoid Nested Queries When Possible

-- Use JOINs or CTEs instead of deeply nested subqueries

Test with LIMIT First

-- Test query results before running on full dataset

SELECT * FROM large_table WHERE condition LIMIT 10;

Use Transactions for Related Changes

START TRANSACTION;

-- Multiple related operations

COMMIT;

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