面试题与答案

A schema defines the structure of a database, including tables, fields, and relationships between tables.

Example:

In a relational database, a schema might include tables for 'users' and 'orders,' with defined fields for each.

An inner join returns only the rows where there is a match in both tables, while a left join returns all rows from the left table and the matched rows from the right table.

Example:

Selecting all customers and their orders, even if some customers have not placed any orders (left join).