How SQL communicates with the database engine - Practice Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does SQL send commands to the database engine?

When you write an SQL query, how does it reach the database engine to be executed?

A The database engine reads SQL queries from a text file on the disk automatically every minute.

B The SQL query is parsed and sent through a database driver or connector which communicates with the database engine.

C SQL queries are directly typed into the database engine's memory without any intermediate step.

D SQL queries are converted into machine code by the operating system before reaching the database engine.

💡 Hint

Think about how applications connect to databases to send queries.

SQL queries are sent through a database driver or connector (like ODBC, JDBC, or native drivers). This driver parses and transmits the query to the database engine, which then executes it.

❓ query_result

intermediate

What is the output of this SQL query communication step?

Consider the following SQL query sent to a database engine:

SELECT name FROM employees WHERE id = 5;

What does the database engine return after processing this query?

A The number 5 as a confirmation of the id searched.

B An error message because the query is incomplete.

C A result set containing the name of the employee with id 5.

D A list of all employee IDs in the database.

💡 Hint

Think about what a SELECT query does and what the WHERE clause filters.

The database engine executes the query and returns a result set with the requested column(s) for rows matching the condition. Here, it returns the name of the employee whose id is 5.

📝 Syntax

advanced

Which SQL command correctly communicates to update a record?

You want to update the salary of an employee with id 10 to 60000. Which SQL command correctly sends this update to the database engine?

A UPDATE employees SET salary = 60000 WHERE id = 10;

B MODIFY employees salary = 60000 WHERE id = 10;

C CHANGE employees SET salary TO 60000 WHERE id = 10;

D ALTER employees salary = 60000 WHERE id = 10;

💡 Hint

Recall the standard SQL command to change existing data in a table.

The correct SQL command to update data is UPDATE. The other options use invalid SQL keywords and will cause syntax errors.

❓ optimization

advanced

How can SQL communication be optimized for faster query execution?

Which of the following methods helps reduce the communication overhead between SQL and the database engine for repeated queries?

A Restarting the database engine before each query to clear memory.

B Writing the full SQL query text every time without any caching.

C Sending queries as plain text files via email to the database administrator.

D Using prepared statements to send the query once and execute multiple times with different parameters.

💡 Hint

Think about how to avoid sending the full query text repeatedly.

Prepared statements allow the database engine to parse and plan the query once, then execute it multiple times with different parameters, reducing communication and processing time.

🔧 Debug

expert

Why does this SQL query fail to communicate properly with the database engine?

Given this SQL query sent to the database engine:

SELEC name FROM employees WHERE id = 3;

What error will the database engine return?

A Syntax error near 'SELEC' because the keyword is misspelled.

B No error; the query runs and returns the name for id 3.

C Permission denied error because SELECT is a restricted command.

D Runtime error due to missing semicolon at the end.

💡 Hint

Check the spelling of SQL keywords carefully.

The keyword SELECT is misspelled as SELEC, causing a syntax error. The database engine cannot parse the query and returns an error indicating the problem near the misspelled word.