LATERAL JOIN in PostgreSQL — Examples & 2025 Guide

Understanding how to use the LATERAL JOIN in PostgreSQL unlocks advanced SQL possibilities, from correlated subqueries to dynamic relationship mapping. Yet, LATERAL syntax can look intimidating and cause confusion even for experienced users. That's where AI2sql platform comes in: it turns plain-English requests into perfect SQL, making complex joins as easy as asking a question.

LATERAL JOIN matters because it enables each row from one table to inform a subquery on the fly, supporting scenarios like top-N per group, JSON manipulation, and row-wise calculations. If you work with PostgreSQL and need flexible, relational data transformations, LATERAL is an essential tool.

What is a LATERAL JOIN in PostgreSQL?

A LATERAL JOIN allows a subquery in the FROM clause to reference columns from tables already defined to its left. This enables row-wise, dependent computations that standard joins can't achieve. Think of it as “for each row in table A, run this subquery using its values.”

Why Use LATERAL JOIN?

• Correlated subqueries: Make subqueries depend on outer rows.

• Top-N per group selection: Find the highest N records related to each parent.

• Flattening arrays or JSON: Unroll complex data per row.

• Advanced reporting & analytics: Calculate stats and aggregations persistently.

Real-World Examples of PostgreSQL LATERAL JOIN

Example 1: Top-1 Order Per Customer

SELECT c.customer_id, c.name, o.order_id, o.total_amount
FROM customers c
LEFT JOIN LATERAL (
  SELECT * FROM orders o
  WHERE o.customer_id = c.customer_id
  ORDER BY o.order_date DESC
  LIMIT 1
) o ON TRUE;

Example 2: Expanding Arrays With LATERAL

SELECT user_id, unnest(roles) AS role
FROM users;

(In true LATERAL syntax:)

SELECT u.user_id, r.role
FROM users u,
LATERAL unnest(u.roles) AS r(role);

Example 3: Row-wise Aggregation

SELECT p.product_id, p.name, s.avg_sales
FROM products p
LEFT JOIN LATERAL (
  SELECT AVG(quantity) AS avg_sales
  FROM sales
  WHERE sales.product_id = p.product_id
) s ON TRUE;

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Try It Yourself

• Try AI2sql LATERAL JOIN Generator

• LATERAL JOIN PostgreSQL Tutorial

• LATERAL JOIN PostgreSQL Examples

Conclusion

LATERAL JOIN in PostgreSQL is a transformational feature for advanced SQL development, unlocking row-by-row computation and flexible subqueries. Yet, writing these queries by hand can stall productivity and introduce subtle mistakes. AI2sql erases this barrier: in plain English, get SQL code that handles LATERAL, subqueries, and all PostgreSQL intricacies — no coding needed, instant results, and enterprise-ready. Trusted by 50,000+ developers and data teams. Want to supercharge your next project? Try AI2sql for free and see how fast and easy SQL can be.