Questions: SQL: SELECT Statement and Basic Queries

Question 1

A table 'employees' has columns: id, name, salary, department. Which query returns only the name and salary columns for every row?

• A. SELECT * FROM employees
• B. SELECT name, salary FROM employees
• C. SELECT employees WHERE columns = name, salary
• D. GET name, salary FROM employees

Answer: (B)

SELECT name, salary FROM employees performs projection — it restricts which columns are returned while keeping all rows. SELECT * returns all columns. The other two options are not valid SQL syntax.

Question 2

Without an ORDER BY clause, a SQL SELECT query guarantees that results are returned in the order the rows were inserted into the table.

• T. True
• F. False

Answer: False

SQL makes no guarantee about row order unless ORDER BY is specified. A database engine is free to return rows in any order that is efficient (e.g., based on index scans or storage layout). Relying on insertion order without ORDER BY is a common mistake that produces unreliable results.

Question 3

In relational algebra terms, what two operations does a basic SELECT ... FROM ... query perform, and how do they map to parts of the SQL syntax?

Model answer: Projection (restricting columns) maps to the column list after SELECT; selection (restricting rows) maps to conditions in the WHERE clause. A query with no WHERE clause performs only projection.

This distinction comes directly from relational algebra: projection keeps certain attributes (columns) while selection keeps certain tuples (rows) matching a predicate. Understanding this mapping makes it easier to reason about what a query will return.