SQL Server DB Administrator Questions And Answers

41⟩ What are user defined datatypes and when you should go for them?

User defined datatypes let you extend the base SQL Server datatypes by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar(8). In this case you could create a user defined datatype called Flight_num_type of varchar(8) and use it across all your tables. See sp_addtype, sp_droptype in books online.

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42⟩ What are statistics, under what circumstances they go out of date, how do you update them?

Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.

Some situations under which you should update statistics:

1) If there is significant change in the key values in the index

2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated

3) Database is upgraded from a previous version

Look up SQL Server books online for the following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats, sp_updatestats

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43⟩ Let's assume you have data that resides on SQL Server 6.5. You have to move it SQL Server 7.0. How are you going to do it?

You have to use transfer command.

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44⟩ How to determine the service pack currently installed on SQL Server?

The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. To know more about this process visit SQL Server service packs and versions.

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45⟩ Explain different types of BACKUPs avaialabe in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, filegroup backup. Check out the BACKUP and RESTORE commands in SQL Server books online. Be prepared to write the commands in your interview. Books online also has information on detailed backup/restore architecture and when one should go for a particular kind of backup.

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46⟩ What is bit datatype and what's the information that can be stored inside a bit column?

Bit datatype is used to store boolean information like 1 or 0 (true or false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype can represent a third state, which is NULL.

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47⟩ What is denormalization and when would you go for it?

As the name indicates, denormalization is the reverse process of normalization. It's the controlled introduction of redundancy in to the database design. It helps improve the query performance as the number of joins could be reduced.

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48⟩ What are the different ways of moving data/databases between servers and databases in SQL Server?

There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT scripts to generate data.

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49⟩ Tell me what are the steps you will take to improve performance of a poor performing query?

This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables. Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer. Download the white paper on performance tuning SQL Server from Microsoft web site.

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50⟩ When you create a database how is it stored?

It is stored in two separate files: one file contains the data, system tables, other database objects, the other file stores the transaction log.

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51⟩ Explain the storage models of OLAP?

Check out MOLAP, ROLAP and HOLAP in SQL Server interview questions guides for more infomation.

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52⟩ What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. What are the advantages and disadvantages of this approach?

Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker. Indexes are of two types. Clustered indexes and non-clustered indexes. When you create a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and it's row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table. If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same t ime, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.

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53⟩ CREATE INDEX myIndex ON myTable(myColumn)What type of Index will get created after executing the above statement?

Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise.

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54⟩ What's the difference between DELETE TABLE and TRUNCATE TABLE commands?

DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back. TRUNCATE TABLE is functionally identical to DELETE statement with no WHERE clause: both remove all rows in the table. But TRUNCATE TABLE is faster and uses fewer system and transaction log resources than DELETE. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table's data, and only the page deallocations are recorded in the transaction log. TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column. If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement. You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint; instead, use DELETE statement without a WHERE clause. Because TRUNCATE TABLE is not logged, it cannot activate a trigger. TRUNCATE TABLE may not be used on tables participating in an indexed view

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55⟩ What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?

This question is generally asked to see how current is your knowledge. Generally there is a section in the beginning of the books online titled "What's New", which has all such information. Of course, reading just that is not enough, you should have tried those things to better answer the questions. Also check out the section titled "Backward Compatibility" in books online which talks about the changes that have taken place in the new version.

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56⟩ What are defaults? Is there a column to which a default can't be bound?

A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can't have defaults bound to them. See CREATE DEFAULT in books online.

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57⟩ How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships. One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships. Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table. It will be a good idea to read up a database designing fundamentals text book.

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58⟩ What is database replication? What are the different types of replication you can set up in SQL Server?

Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios: ? Snapshot replication ? Transactional replication (with immediate updating subscribers, with queued updating subscribers) ? Merge replication See SQL Server books online for indepth coverage on replication. Be prepared to explain how different replication agents function, what are the main system tables used in replication etc.

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59⟩ What are different types of BACKUPs available in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, filegroup backup.

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60⟩ What is the difference between DELETE TABLE and TRUNCATE TABLE commands?

DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back.

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SQL Server DB Administrator

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84 SQL Server DB Administrator Questions And Answers

41⟩ What are user defined datatypes and when you should go for them?

42⟩ What are statistics, under what circumstances they go out of date, how do you update them?

43⟩ Let's assume you have data that resides on SQL Server 6.5. You have to move it SQL Server 7.0. How are you going to do it?

44⟩ How to determine the service pack currently installed on SQL Server?

45⟩ Explain different types of BACKUPs avaialabe in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

46⟩ What is bit datatype and what's the information that can be stored inside a bit column?

47⟩ What is denormalization and when would you go for it?

48⟩ What are the different ways of moving data/databases between servers and databases in SQL Server?

49⟩ Tell me what are the steps you will take to improve performance of a poor performing query?

50⟩ When you create a database how is it stored?

51⟩ Explain the storage models of OLAP?

52⟩ What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. What are the advantages and disadvantages of this approach?

53⟩ CREATE INDEX myIndex ON myTable(myColumn)What type of Index will get created after executing the above statement?

54⟩ What's the difference between DELETE TABLE and TRUNCATE TABLE commands?

55⟩ What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?

56⟩ What are defaults? Is there a column to which a default can't be bound?

57⟩ How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

58⟩ What is database replication? What are the different types of replication you can set up in SQL Server?

59⟩ What are different types of BACKUPs available in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

60⟩ What is the difference between DELETE TABLE and TRUNCATE TABLE commands?

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SQL Server DB Administrator

Home MS SQL Server SQL Server DB Administrator

84 SQL Server DB Administrator Questions And Answers

41⟩ What are user defined datatypes and when you should go for them?

42⟩ What are statistics, under what circumstances they go out of date, how do you update them?

43⟩ Let's assume you have data that resides on SQL Server 6.5. You have to move it SQL Server 7.0. How are you going to do it?

44⟩ How to determine the service pack currently installed on SQL Server?

45⟩ Explain different types of BACKUPs avaialabe in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

46⟩ What is bit datatype and what's the information that can be stored inside a bit column?

47⟩ What is denormalization and when would you go for it?

48⟩ What are the different ways of moving data/databases between servers and databases in SQL Server?

49⟩ Tell me what are the steps you will take to improve performance of a poor performing query?

50⟩ When you create a database how is it stored?

51⟩ Explain the storage models of OLAP?

52⟩ What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. What are the advantages and disadvantages of this approach?

53⟩ CREATE INDEX myIndex ON myTable(myColumn)What type of Index will get created after executing the above statement?

54⟩ What's the difference between DELETE TABLE and TRUNCATE TABLE commands?

55⟩ What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?

56⟩ What are defaults? Is there a column to which a default can't be bound?

57⟩ How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

58⟩ What is database replication? What are the different types of replication you can set up in SQL Server?

59⟩ What are different types of BACKUPs available in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

60⟩ What is the difference between DELETE TABLE and TRUNCATE TABLE commands?

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