Writing simple queries

In general, a "query" means a "question". Within the realm of databases, a query fetches information from the database objects such as tables and views. We can combine one or more tables/views in a single query. In this chapter, we will execute queries using the SQL*Plus environment. However, you may prefer to use either SQL Developer or SQL*Plus.

To list columns of a table we use the DESC command in SQL*Plus:

SQL> DESC employees

Now, let us execute a simple query against the employees table and fetch a few columns:

SQL> SELECT employee_id, first_name, last_name, job_id FROM employees;

We can restrict the results returned by the query using the WHERE clause as shown below:

SQL> SELECT employee_id, first_name, last_name, job_id FROM employees WHERE salary < 2500;