20 Dynamic SQL Interview Questions and Answers

Dynamic SQL is a powerful tool for developers who need to generate SQL code at runtime. This can be used to build complex queries or to dynamically generate test data. While Dynamic SQL can be a great asset, it can also be a source of confusion during an interview. In this article, we will review some common Dynamic SQL questions and how you can answer them.

Dynamic SQL Interview Questions and Answers

Here are 20 commonly asked Dynamic SQL interview questions and answers to prepare you for your interview:

1. What is dynamic SQL?

Dynamic SQL is a type of SQL that is not hard-coded, but rather generated at runtime. This means that the SQL statement is not known until the program is run. Dynamic SQL can be used to increase the flexibility of a program and make it easier to customize SQL statements for different situations.

2. How does dynamic SQL work?

Dynamic SQL is a programming technique that allows you to build SQL statements dynamically at runtime. This means that you can construct SQL statements on the fly, based on user input or other conditions, and then execute those statements immediately. This can be a powerful tool for creating more flexible and responsive applications.

3. Can you give me some examples of how dynamic SQL can be used in a real-world scenario?

Dynamic SQL can be used in a number of scenarios where the specific SQL query to be executed is not known in advance. For example, if you are building a search feature for a website, you may not know what keywords the user will enter. In this case, you could use dynamic SQL to construct the SQL query on the fly based on the user’s input. Another example might be if you are building a reporting tool that allows users to select different criteria for generating a report. Again, you would not know in advance what combination of criteria the user would select, so you would need to use dynamic SQL to construct the SQL query dynamically.

4. Why do we use EXECUTE IMMEDIATE to execute dynamically created queries instead of simply using the query directly?

EXECUTE IMMEDIATE is used to execute dynamically created queries because it can take a string as input and execute it as if it were a normal SQL statement. This is useful for creating queries on the fly that can take advantage of different input parameters.

5. Can you explain the difference between static and dynamic SQL?

Static SQL is SQL that is hard-coded and does not change based on user input. Dynamic SQL is SQL that is generated at runtime based on user input. Static SQL is typically more efficient because the database can optimize the query before it is executed. However, dynamic SQL can be more flexible because it can be customized for each user.

6. What are some common problems with dynamic SQL?

One common problem with dynamic SQL is that it can be difficult to debug because the code is not always visible. Additionally, dynamic SQL can be less efficient than static SQL because it often requires more parsing and compilation. Finally, dynamic SQL can be more susceptible to SQL injection attacks.

7. What’s your understanding of cursors and their usage in dynamic SQL?

A cursor is a temporary work area created in the system memory when a SQL statement is executed. A cursor contains information on a select statement and the rows of data accessed by it. This allows the rows to be retrieved one at a time. In dynamic SQL, cursors are used to fetch data from the database one row at a time and process it as required.

8. What is the maximum number of characters allowed by DBMS_SQL for dynamic SQL statements?

DBMS_SQL allows for a maximum of 32767 characters for dynamic SQL statements. This limit is due to the fact that DBMS_SQL uses a VARCHAR2 data type to store the SQL statement, which has a maximum length of 32767 characters.

9. What are the different ways you can use when executing dynamic SQL statements?

There are four different ways that you can execute dynamic SQL statements:

1. EXECUTE statement
2. sp_executesql
3. OPENQUERY
4. OPENROWSET

10. Do you think that it’s possible to pass parameters to a query string before execution, or will this lead to security issues?

It is possible to pass parameters to a query string before execution, but this can lead to security issues if the parameters are not properly sanitized. If you are going to do this, it is important to make sure that you are only passing in valid parameters that will not cause any issues when the query is executed.

11. Are there any limitations on the kind of SQL statements that can be executed using Dynamic SQL?

There are some limitations on the kind of SQL statements that can be executed using Dynamic SQL. For example, you cannot use Dynamic SQL to execute a DDL statement, such as CREATE TABLE. Additionally, Dynamic SQL does not support the use of certain SQL keywords, such as the WITH clause.

12. In what situations would it be best to avoid using dynamic SQL?

There are a few situations where it might be best to avoid using dynamic SQL. If you are working with a large amount of data, dynamic SQL can be slow. Additionally, if you are working with sensitive data, dynamic SQL can be a security risk since it can be difficult to control what is being executed. Finally, if you are working with data that is subject to change often, dynamic SQL can be difficult to maintain.

13. Which one is better: Stored Procedures or Dynamic SQL?

It really depends on the situation. If you know that your SQL code is going to be relatively static and not change often, then stored procedures can be a good choice. They can be faster and more efficient since they are already compiled and ready to go. However, if your SQL code is going to be changing often or is particularly complex, then dynamic SQL might be a better choice. It can be more flexible and easier to change on the fly.

14. Does dynamic SQL cause performance problems? If yes, then how should they be solved?

Dynamic SQL can cause performance problems if it is not used correctly. One way to avoid these problems is to use parameterized queries instead of concatenating strings together to form a query. This will help to avoid SQL injection attacks and will also make sure that the query is optimized before it is executed.

15. What are some best practices for developing dynamic SQL?

Some best practices for developing dynamic SQL include using parameterized queries to avoid SQL injection attacks, using stored procedures whenever possible, and using a least privilege approach when granting permissions to users.

16. What are the advantages of using dynamic SQL?

Dynamic SQL has a number of advantages, chief among them being that it can be used to write code that is more flexible and adaptable. With dynamic SQL, you are not limited to a set number of parameters or a specific structure, which means that you can write code that is more easily reusable and that can be more easily modified to meet changing needs. Additionally, dynamic SQL can be used to write code that is more efficient, as it can be specifically tailored to the data that it will be working with.

17. Can you give an example of where “dynamic SQL” may not be appropriate?

One example where dynamic SQL may not be appropriate is when your application is going to be handling user input directly. If you’re not careful, dynamic SQL can introduce security vulnerabilities into your application. For example, if you’re concatenating user input directly into your SQL query string, a malicious user could enter SQL code that would be executed by your database server.

18. Is it possible to write recursive queries using dynamic SQL?

Yes, it is possible to write recursive queries using dynamic SQL. However, it is generally considered to be bad practice to do so, as it can lead to issues with performance and maintainability. If you absolutely need to write a recursive query, it is recommended that you use a stored procedure instead.

19. What are some alternatives to dynamic SQL?

There are a few alternatives to dynamic SQL, depending on what your specific needs are. If you need to generate SQL dynamically but don’t want to use dynamic SQL specifically, you could use a stored procedure. If you need to generate SQL dynamically but want to avoid the potential for SQL injection attacks, you could use parameterized queries. Finally, if you need to generate SQL dynamically but want to make sure that the generated SQL is still readable and maintainable, you could use template queries.

20. Why do we need dynamic SQL if stored procedures already exist?

Dynamic SQL is useful when you need to generate SQL on the fly, based on user input or other conditions. For example, you might use dynamic SQL to generate a query that returns data for a specific date range, or for a specific customer. Stored procedures are useful for storing and executing SQL that is not going to change, or that is not going to be generated dynamically.