DB2 Interview Questions

Top 50 DB2 interview questions and answers with examples to help you prepare for a DB2 interview:

1. What is DB2?

Answer: DB2 is a relational database management system (RDBMS) developed by IBM.

2. Explain the difference between DB2 and SQL.

Answer: DB2 is a specific RDBMS product, whereas SQL is a language used to interact with relational databases. SQL can be used with DB2.

3. What are the different types of DB2 environments?

Answer: DB2 has three main environments: Single Partition, Data Sharing, and Client/Server.

4. What is a tablespace in DB2?

Answer: A tablespace is a storage structure used to organize and manage data in DB2. Tables and indexes are stored in tablespaces.

5. What is a DB2 package?

Answer: A DB2 package is a collection of SQL statements that are precompiled and stored in the database for execution.

6. Explain the concept of isolation levels in DB2.

Answer: Isolation levels determine the level of data consistency in a DB2 transaction. The four isolation levels in DB2 are UR (Uncommitted Read), CS (Cursor Stability), RS (Read Stability), and RR (Repeatable Read).

7. How do you take a backup of a DB2 database?

Answer: You can use the db2 backup command to take a backup of a DB2 database. For example: db2 backup database mydb to /backupdir.

8. What is a DB2 alias?

Answer: A DB2 alias is an alternative name for a table or view. It can be used for data security or to simplify complex SQL statements.

9. What is the purpose of the DB2 catalog?

Answer: The DB2 catalog contains metadata about the database, such as table definitions, indexes, and access plans.

10. How do you retrieve all rows from a DB2 table?

Answer: You can use a simple SQL statement to retrieve all rows: SELECT * FROM mytable.

11. Explain the difference between CHAR and VARCHAR data types in DB2.

Answer: CHAR is a fixed-length character data type, while VARCHAR is a variable-length character data type. CHAR always uses the specified length, while VARCHAR uses only as much space as needed.

12. What is an index in DB2?

Answer: An index in DB2 is a data structure that improves the speed of data retrieval operations on a table. It contains a subset of the columns from the table and their corresponding values.

13. What is a stored procedure in DB2?

Answer: A stored procedure in DB2 is a set of SQL statements that can be executed as a single unit. It is stored in the database and can be called by applications.

14. How do you create a new table in DB2?

Answer: You can create a new table using the CREATE TABLE SQL statement. For example:

CREATE TABLE mytable (

    id INT NOT NULL,

    name VARCHAR(255),

    PRIMARY KEY (id)

);

15. What is a foreign key in DB2?

Answer: A foreign key is a constraint that enforces referential integrity between two tables. It ensures that the values in one table's column match the values in another table's primary key column.

16. How do you update data in a DB2 table?

Answer: You can use the UPDATE statement to modify data in a DB2 table. For example:

UPDATE mytable

SET name = 'NewName'

WHERE id = 1;

17. What is a DB2 cursor?

Answer: A cursor in DB2 is a database object used to retrieve and manipulate data row by row. Cursors are often used in stored procedures and application programs.

18. How do you delete data from a DB2 table?

Answer: You can use the DELETE statement to remove data from a DB2 table. For example:

DELETE FROM mytable

WHERE id = 1;

19. Explain the ACID properties of DB2 transactions.

Answer: ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are reliable and maintain data integrity.

20. What is the purpose of the DB2 LOCKLIST parameter?

Answer: The LOCKLIST parameter in DB2 specifies the maximum number of locks that can be held simultaneously by all applications.

21. How do you retrieve the current date and time in DB2?

Answer: You can use the CURRENT TIMESTAMP function to get the current date and time in DB2. For example:

SELECT CURRENT TIMESTAMP FROM sysibm.sysdummy1;

22. What is the purpose of the DB2 EXPLAIN statement?

Answer: The EXPLAIN statement in DB2 is used to analyze and optimize the execution plan of SQL statements. It provides information about how DB2 will access and process data.

23. Explain the difference between an inner join and an outer join in DB2.

Answer: An inner join returns only the rows that have matching values in both tables, while an outer join returns all rows from one table and the matching rows from the other table. Outer joins include LEFT, RIGHT, and FULL OUTER joins.

24. What is the purpose of the DB2 LOAD utility?

Answer: The DB2 LOAD utility is used to load large amounts of data into a DB2 table efficiently.

25. How do you create an index on a DB2 table column?

Answer: You can create an index on a table column using the CREATE INDEX statement. For example:

CREATE INDEX myindex

ON mytable (column_name);

26. What is a DB2 package bind process?

Answer: The package bind process in DB2 compiles and binds SQL statements in a package to generate access plans for efficient execution.

27. Explain the purpose of the DB2 COMMIT and ROLLBACK statements.

Answer: The COMMIT statement is used to save the changes made in a transaction, while the ROLLBACK statement is used to undo the changes and restore the database to its previous state.

28. What is a DB2 buffer pool?

Answer: A buffer pool in DB2 is a memory area used to cache frequently accessed data pages. It improves data retrieval performance.

29. How do you retrieve the count of rows in a DB2 table?

Answer: You can use the COUNT function to retrieve the count of rows in a DB2 table. For example:

SELECT COUNT(*) FROM mytable;

30. What is the purpose of the DB2 RUNSTATS utility?

Answer: The RUNSTATS utility in DB2 is used to collect statistics about table and