Database Management System Interview Questions and Answers For Freshers and Experience Part-11
101. What are the four objectives of the selection of a data type?
A data type should be selected so that all possible values are represented using minimal storage space. The data type should help to ensure data integrity and support all possible data manipulations (i.e., cannot place a letter in a field such as salary where a number is required).
102. Describe the four types of indexes.
A unique primary index is unique and is used to find and store a row. A nonunique primary index is not unique and is used to find a row but also where to store a row (based on its unique primary index). A unique secondary index is unique for each row and used to find table rows. A nonunique secondary index is not unique and used to find table rows.
103. What is denormalization and why would someone consider doing so?
Denormalization is the process of taking normalized relations and changing them so that they are not longer normalized. This process may lead to anomalies and create data redundancy as negative consequences. However, the revised relations should improve database performance.
104. Compare a hierarchical and network database model?
The hierarchical model is a top-down structure where each parent may have many children but each child can have only one parent. This model supports one-to-one and one-to-many relationships. The network model can be much more flexible than the hierarchical model since each parent can have multiple children but each child can also have multiple parents. This model supports one-to-one, one-to-many, and many-to-many relationships.
105. Describe the differences between vertical and horizontal portioning.
Horizontal portioning is where the rows in a relation are separated by some criteria and placed into a new relation or file with the same layout as the original relation (in this case only the records in each file differ). Vertical portioning is where the columns in a relation are separated by some criteria and placed into a new relation or file with a different layout as the original relation.
106. Explain the difference between a dynamic and materialized view.
A dynamic view may be created every time that a specific view is requested by a user. A materialized view is created and or updated infrequently and it must be synchronized with its associated base table(s).
107. Discuss some of the techniques that can be used to tune operational performance.
Choosing primary and secondary keys can increase the speed of row selection, joining, and row ordering. Selecting the appropriate file organization for base tables and indexes can also improve performance. Clustering related rows together and maintaining statistics about tables and indexes can lead to increased efficiency.
108. Briefly describe the three types of SQL commands.
Data definition language commands are used to create, alter, and drop tables. Data manipulation commands are used to insert, modify, update, and query data in the database. Data control language commands help the DBA to control the database.
109. What are the steps to follow when preparing to create a table?
1. Identify the data type, length, and precision for each attribute. 2. Identify the columns that can accept a null value. 3. Identify the columns that need to be unique. 4. Identify primary and related foreign keys with the parent table being created before the child. 5. Determine default values. 6. Determine where the domain values are that need to be constrained. 7. Create the indexes.
110. What are some disadvantages of a standard language such as SQL?
A standard language can hinder the effort to create a new language. One standard is never enough to meet all of the business needs. A standard can be a compromise among interested parties which can cause the standard to not be ideal. If a standard is altered by some, than portability between platforms could be hurt.