An SQL Optimizer works by analyzing the SQL query and the database schema. It then generates multiple execution plans and selects the one with the lowest cost, which could be in terms of time, memory, or other resources. This process involves several steps:
Parsing: The SQL query is parsed to check for syntax errors and to understand its structure. Query Rewrite: The query may be rewritten to a more efficient form. Cost Estimation: Multiple execution plans are generated, and their costs are estimated. Plan Selection: The execution plan with the lowest cost is selected.