Left Join

Definitions

1. A SQL join that returns all rows from the left (first) table and the matching rows from the right (second) table, filling in NULLs for right-side columns when no match exists. Formally known as LEFT OUTER JOIN.

   In plain English: A way to combine two database tables that keeps every row from the first table, even if there is no matching row in the second.

   Example: "Use a left join from users to orders so we still see users who haven't purchased anything — they'll just have NULL order IDs."

Related Terms

• Query
• Table
• Query Plan
• Index Scan vs Seq Scan
• Upsert
• Database Trigger
• KV Store
• MySQL
• Outer Join
• PostgreSQL
• Primary Key
• Query Builder
• Query Engine
• Rails Migration
• Raw SQL
• RDBMS
• SQLite