MySQL vs PostgreSQL vs SQL Server overview - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Which database supports JSON data type natively?

Among MySQL, PostgreSQL, and SQL Server, which one supports JSON as a native data type allowing efficient querying and indexing?

A Both MySQL and PostgreSQL support JSON natively.

B Only PostgreSQL supports JSON natively.

C Only MySQL supports JSON natively.

D None of them support JSON natively.

💡 Hint

Think about which databases allow storing JSON documents and querying them efficiently.

Both MySQL (from version 5.7) and PostgreSQL support JSON data types natively, allowing efficient storage and querying. SQL Server supports JSON but stores it as plain text without a native JSON type.

❓ query_result

intermediate

Identify the database by its default case sensitivity in string comparisons

Given the following behavior: String comparisons are case-insensitive by default in this database. Which database is it?

A MySQL

B PostgreSQL

C SQL Server

D All three are case-sensitive by default

💡 Hint

Consider which database treats 'abc' and 'ABC' as equal by default in WHERE clauses.

MySQL and SQL Server use case-insensitive collation by default for string comparisons, making them case-insensitive unless specified otherwise. PostgreSQL is case-sensitive by default.

📝 Syntax

advanced

Which SQL syntax is valid for limiting query results in all three databases?

You want to limit the number of rows returned by a query to 5. Which of the following SQL statements will work correctly in MySQL, PostgreSQL, and SQL Server?

SQL

SELECT * FROM employees FETCH FIRST 5 ROWS ONLY;

A SELECT * FROM employees WHERE ROWNUM <= 5;

B SELECT TOP 5 * FROM employees;

C SELECT * FROM employees LIMIT 5;

D SELECT * FROM employees FETCH FIRST 5 ROWS ONLY;

💡 Hint

Think about the SQL standard syntax supported by all three databases.

The syntax 'FETCH FIRST 5 ROWS ONLY' is part of the SQL standard and supported by PostgreSQL, SQL Server (2012+), and MySQL (8.0+). LIMIT works in MySQL and PostgreSQL but not SQL Server. TOP is SQL Server specific. ROWNUM is Oracle specific.

❓ optimization

advanced

Which database supports partial indexes for query optimization?

Partial indexes allow indexing only a subset of rows in a table. Which database supports partial indexes natively?

A PostgreSQL

B MySQL

C SQL Server

D None of them support partial indexes

💡 Hint

Think about which database allows creating indexes with a WHERE clause.

PostgreSQL supports partial indexes, allowing indexes on a subset of rows using a WHERE clause. MySQL and SQL Server do not support partial indexes natively.

🔧 Debug

expert

Why does this SQL Server query fail but works in MySQL and PostgreSQL?

Consider this query: SELECT * FROM orders WHERE order_date = '2023-02-30'; It runs (with warning) in MySQL but fails in SQL Server and PostgreSQL. Why?

A SQL Server requires dates to be in ISO 8601 format only.

B MySQL automatically converts invalid dates to NULL silently.

C SQL Server strictly validates date literals and '2023-02-30' is invalid.

D MySQL treats all strings as valid dates regardless of format.

💡 Hint

Think about how each database handles invalid date values.

SQL Server and PostgreSQL validate date literals strictly and throw an error for invalid dates like '2023-02-30'. MySQL issues a warning but allows the query to run, converting invalid dates silently.