An SQL compiler is a tool that translates SQL (Structured Query Language) queries, written by developers or users, into a format that a database management system (DBMS) can execute. Unlike traditional compilers that convert high-level code into machine code, an SQL compiler converts SQL statements into an execution plan, which is a series of low-level operations that the database engine can perform to retrieve, update, or manipulate data stored in a relational database.

The SQL compilation process involves several steps:

1. Parsing: The SQL compiler first parses the SQL query to check for syntax errors and ensure that the query conforms to the SQL language rules.

2. Optimization: Once the query is parsed, the compiler optimizes it by determining the most efficient way to execute the query. This step might involve choosing the best indexes, determining join orders, and selecting the most efficient algorithms for data retrieval.

3. Execution Plan Generation: The final step is to generate an execution plan, which is a detailed, step-by-step guide that the DBMS follows to execute the query. The plan is then passed to the database engine for execution.

Understanding the role of an SQL compiler helps developers write more efficient queries and better understand how their queries are processed by the database, leading to improved performance and optimized database interactions.