Questions

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1What are functions and operators in MySQL, and how are they different?

2What is the difference between single-row functions and aggregate functions?

3Give examples of commonly used string functions in MySQL.

4What is the use of the CONCAT() function? How is it different from using ||?

5Explain the difference between NOW(), CURDATE(), and SYSDATE().

6What are arithmetic operators in MySQL? Give examples.

7What is the difference between the = and <=> operators?

8What does the DISTINCT keyword do when used with aggregate functions like COUNT()?

9What is the difference between IFNULL() and COALESCE() functions?

10What are logical operators in MySQL, and how do AND, OR, and NOT work?

11What is the difference between LENGTH() and CHAR_LENGTH() functions?

12How does MySQL handle type conversion when using operators on different data types?

13What is the difference between ROUND(), TRUNCATE(), and FORMAT() functions?

14Explain how CASE and IF() functions can be used for conditional logic.

15What are comparison operators in MySQL, and how are they used with NULL values?

16How do aggregate functions like AVG(), SUM(), and MAX() behave when NULLs are present?

17Explain the use of REGEXP and LIKE operators. What’s the difference between them?

18What are user-defined functions (UDFs), and how do they differ from stored procedures?

19What are the differences between DATE_ADD() and ADDDATE() functions?

20How can you use STR_TO_DATE() and DATE_FORMAT() for converting and displaying date values?

21How does MySQL internally optimize and cache results of deterministic functions?

22What are window functions in MySQL 8.0, and how do they differ from aggregate functions?

23Explain the difference between RANK(), DENSE_RANK(), and ROW_NUMBER() window functions.

24How does MySQL evaluate operator precedence when multiple operators are used in a single expression?

25Can functions be used in the WHERE clause? What are the performance implications?

26How can you use JSON_EXTRACT() and JSON_CONTAINS() to work with JSON data in MySQL?

27What are the performance trade-offs of using scalar functions inside JOIN or GROUP BY clauses?

28Explain how collation affects comparison operators in string functions.

29What are deterministic and non-deterministic functions? How does this affect replication and indexes?

30How would you combine multiple functions and operators to clean, transform, and aggregate data efficiently in one query?

mysql

Functions and Operators

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What are user-defined functions (UDFs), and how do they differ from stored procedures?

User-Defined Functions (UDFs) vs Stored Procedures in MySQL

User-defined functions (UDFs) and stored procedures are both reusable database routines in MySQL, but they differ in purpose, behavior, and how they are used in queries.

1. User-Defined Functions (UDFs)

1
Return a single value (scalar) every time they are called.
2
Can be used inside SQL expressions (e.g., SELECT, WHERE, ORDER BY).
3
Must not modify data (no INSERT, UPDATE, DELETE, or transactions).
4
Must return a value using RETURN.
5
Are deterministic or non-deterministic, depending on their logic.

UDF Example

2. Stored Procedures

1
Perform a sequence of operations—often complex logic.
2
Can return zero, one, or many values (via OUT parameters or result sets).
3
Can modify data (INSERT, UPDATE, DELETE allowed).
4
Cannot be used inside SELECT statements.
5
Support control flow, loops, and exception handling.

Stored Procedure Example

3. Key Differences Between UDFs and Stored Procedures

1
UDFs return a single value; procedures can return multiple values.
2
UDFs cannot change database state; procedures can.
3
UDFs are called inside SQL queries; procedures are invoked with CALL.
4
UDFs must be deterministic to be optimized; procedures do not require this.
5
Procedures support complex logic, loops, and error handling; UDFs do not.

In summary: Use UDFs for computations within queries that return a value, and use stored procedures for performing operations, workflows, or multi-step logic on the database.