This document contains 20 questions and answers about IBM DB2 concepts. It covers topics such as foreign keys, the SELECT statement syntax, the use of the WHERE clause, different types of joins for retrieving data from multiple tables, DDL and DML statements, views and their purpose, outer joins, subselects vs nested selects, the difference between GROUP BY and ORDER BY, the EXPLAIN statement, table spaces, cursors and their function, referential integrity, factors that impact DB2 system performance such as CPU vs I/O, advantages of denormalizing tables, the database descriptor and lock contention, SPUFI, parameters that control free space in DB2 such as PCTFREE and FREEPAGE, and

1. IBM DB2 Interview Questions and Answers
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1. What are foreign keys?
These are attributes of one table that have matching values in a primary key in another table,
allowing for relationships between tables.
2. Describe the elements of the SELECT query syntax
SELECT element FROM table WHERE conditional statement .
3. Explain the use of the WHERE clause
WHERE is used with a relational statement to isolate the object element or row.
4. What techniques are used to retrieve data from more than one table in a single
SQL Statements?
Joins, unions and nested selects are used to retrieve data
5. What do the initials DDL and DML stand for and what is their meaning?
DDL is data definition language and DML is data manipulation language DDL
statements are CREATE, ALTER, TRUNCATE DML statements are SELECT, INSERT,
DELETE and UPDATE .
6. What is a view? Why use it?
A view is a virtual table made up of data from base tables and other views, but not stored
separately.
7. Explain an outer join
An outer join includes rows from tables when there are no matching values in the Tables.
8. What is a sub select? Is it different from a nested select?
Sub select is a select which works in conjunction with another select A nested select is a
kind of Sub Select where the inner select passes to the where criteria for the outer select.
9. What is the difference between group by and order by?
Group by controls the presentation of the rows, order by controls the presentation of the
columns for the results of the SELECT statement .
10. Explain the EXPLAIN statement
The explain statement provides information about the optimizer's choice of access path of
the SQL.
11. What is Table Space?

2. Tables are stored in Table Space (hence the name)! There are three types of Table Space
simple, segmented and partitioned
12. What is a cursor and what is its function?
An embedded Sql statement may return a number of rows while the programming
language can only access one row at a time The programming device called a cursor
controls the position of the row .
13. What is referential integrity?
Referential integrity refers to the consistency that must be maintained between primary
and foreign keys, ie every foreign key value must have a corresponding primary key
value.
14.Usually, which is more important for DB2 system performance - CPU processing
or I/O access?
I/O operations are usually most critical for DB2 performance (or any other database for
that matter)
15. Is there any advantage to De normalizing DB2 tables?
De-normalizing DB2 tables reduces the need for processing intensive relational joins and
reduces the number of foreign keys.
16. What is the database descriptor ?
The database descriptor, DBD is the DB2 component that limits access to the database
whenever objects are created, altered or dropped.
17. What is lock contention?
To maintain the integrity of DB2 objects the DBD permits access to only on object at a
time Lock contention happens if several objects are required by contending application
processes simultaneously.
18. What is SPUFI?
SPUFI stands for SQL processing using File input It is the DB2 interactive menu-driven
tool used by developers to create database objects
19. What is the significance of DB2 free space and what parameters control it?
The two parameters used in the CREATE statement are the PCTFREE which specifies
the percentage of free space for each page and FREEPAGE which indicates the number
of pages to be loaded with data between each free page Free space allows room for the
insertion of new rows
20. What is a NULL value? What are the pros and cons of using NULLS?
A NULL value takes up one byte of storage and indicates that a value is not present as
opposed to a space or zero value It's the DB2 equivalent of TBD on an organizational
chart and often correctly portrays a business situation Unfortunately, it requires extra
coding for an application program to handle this situation