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TSQL Interview Questions – Part 5
Next part of TSQL Interview Questions, contd. from my previous post.
101. What are the required/mandatory parameters that have to be passed with RAISEERROR statement?
- message _id or message_str
- severity, and
- state
102. Difference between RAISEERROR and THROW
103. What severity level errors are managed in TRY-CATCH block?
104. What are row constructors?
New way to insert multiple records in a table with INSERT statement. Also known as Table Value Constructor.
More on: http://msdn.microsoft.com/en-us/library/dd776382.aspx
105. What is SCD (Slowly Changing Dimensions)? What are its types?
106. How many types of internal joins are there in SQL Server?
- Nested loop join
- Merge join
- Hash join
More on: http://msdn.microsoft.com/en-us/library/ms191426.aspx
107. What are pages in SQL Server? How many types of pages are there?
A page in SQL Server is an 8 KB data storage area.
There are 8 types of pages:
1. Data
2. Index
3. Text/Image
4. Global Allocation Map, Shared Global Allocation Map
5. Page Free Space
6. Index Allocation Map
7. Bulk Changed Map
8. Differential Changed Map
More on: http://msdn.microsoft.com/en-us/library/ms190969.aspx
108. How many data sources are available in SSIS?
- DataReader Source in 2005 & ADO NET Source in 2008 & above.
- Excel Source
- Flat File Source
- OLE DB Source
- Raw File Source
- Script Component
- XML Source
109. How will you deploy an SSIS package in testing, staging & production environments?
The dtutil is the command prompt utility which is used to manage SSIS packages.
This utility can copy, move, delete or verify the existence of a package.
More on: http://msdn.microsoft.com/en-us/library/ms162820.aspx
110. Where will you use Conditional Split transformation?
More info: http://msdn.microsoft.com/en-us/library/ms137886.aspx
111. What is live lock, deadlock and what is Lock escalation?
112. If you are working on a SQL database and if suddenly a developer changes the code and your queries results start giving errors, how will you check using a T-SQL query (on system tables) that what has changed in the database.
select o.name, o.object_id, o.modify_date, c.text
from sys.objects o
join sys.syscomments c
on o.object_id = c.id
113. Difference between Nested loops join, Merge join & Hash Join.
114. What are surrogate keys in a data warehouse?
… I’ll be adding more questions on upcoming post.
Comments welcome!!!
TSQL Interview Questions – Part 4
Next part of TSQL Interview Questions, contd. from my previous post.
76. What are Running totals and how would you calculate them? Create a single SQL statement starting with SELECT or ;WITH.
http://sqlwithmanoj.wordpress.com/2011/07/04/calculating-running-totals/
77. What are the various SSIS logging mechanisms?
- Text file
- SQL Server Profiler
- SQL Server
- Windows Event Log
- XML File
MS BOL link: http://msdn.microsoft.com/en-us/library/ms140246.aspx
78. On which table the SSIS SQL Server logs are stored?
On 2005 its sysdtslog90 & on 2008 its sysssislog.
More on SSIS logging on: http://sqlwithmanoj.wordpress.com/2011/06/15/logging-in-ssis-using-sql-server-log-provider/
79. Reverse a String value without using REVERSE() function and WHILE loop. Should be a single SQL statement/query.
http://sqlwithmanoj.wordpress.com/2011/08/18/reverse-a-string-without-using-tsqls-reverse-function/
80. What is the use of BCP utility in SQL Server and how will you use it?
http://sqlwithmanoj.wordpress.com/2011/09/09/bcp-in-out-queryout-the-bcp-util/
81. Is there any difference between Excel Source in SSIS 2005 & 2008?
http://social.msdn.microsoft.com/Forums/en-US/sqlintegrationservices/thread/ea770da2-6f0c-41c4-8093-52b5df73f460/#4267c1f1-74a0-4e2c-b5a4-e2909bf4e5f4
82. Difference between Bookmark lookup & RID lookup?
83. How nested transactions behave?
Here is a scenario:
I have a transaction T and inside this there are 2 transactions T1 AND T2.
If TRANSACTION T2 fails then what happens to transaction T and T1
84. How will you check if a stored procedure with 500 line of code is running very slow? What steps will you take to optimize it?
85. New features in SQL Server 2005 compared to SQL Server 2000 you’ve worked with.
PIVOT, UNPIVOT, Ranking functions (row_number, rank, dense_rank, ntile), CTEs, Grouping sets (ROLUP, CUBE), Intersect, Except, OUTPUT clause, Merge statement, Try-Catch, BIDS (SSIS, SSRS, SSAS), CLR, SMO.
New datatypes: XML, VARCHAR(max), NVARCHAR(max), VARBINARY(max) deprecating the TEXT, NTEXT AND IMAGE datatypes.
XML indexes.
Database (SMTP) mail, SSMS, DMVs, Express Edition, Service Broker, Data Encryption, MARS
86. How will you copy unique records from duplicates in source to destination in SSIS?
87. What transformation will you use to concatenate First name and Last name in SSIS?
88. What do you mean by selectivity of a column/table?
The selectivity is what goes with the cardinality concept. The “cardinality” refers to the number of “distinct” values, as in the set theory so, take a column “SEX”. The possible values are “male” and “female” (ignoring for the moment other possible values like “unknown” or even “other”) … so, your cardinality for that column would be 2, no matter how many rows you have in that table.
The selectivity is the “number of rows” / “cardinality”, so if you have 10K customers, and search for all “female”, you have to consider that the search would return 10K/2 = 5K rows, so a very “bad” selectivity.
The column for the primary key on the other side is “unique”, and hence the cardinality is equal to the number of rows, by definition. So, the selectivity for searching a value in that column will be 1, by definition, which is the best selectivity possible.
89. Difference between EXISTS & IN, which one gives good performance?
90. What output will “SELECT 1/2″ statement give?
0, it will give zero.
91. What is Database Partitioning?
This involves 4 steps:
1. Create Database with different file groups
2. Create Partition Function
3. Create Partition Scheme
4. Create Partitioned Table or Index
92. What is the use of NOLOCK option?
93. How many types of recovery models are available for a database?
1. Simple
2. Bulk logged
3. Full
94. How many types of temporary tables are there in SQL Server?
- Local Temp tables (#)
- Global temp tables (##)
- Table variables (@)
95. In how many ways you can get a table’s row count?
--// 1. Using COUNT(*)
Select count(*) from Person.Contact
--// 2. using COUNT(1)
select count(1) from Person.Contact
--// 3. Using SUM() aggregate function
select sum(1) from Person.Contact
--// 4. Using sysindexes view
select object_name(id), rows from sys.sysindexes where object_name(id) = 'Contact' and indid<2
--// 5. Using sp_spaceused system SP
exec sp_spaceused 'Person.Contact'
--// 6. Using DBCC CHECKTABLE function
DBCC CHECKTABLE('Person.Contact')
--// Note: Before running 5 & 6 you may need to run this script:
DBCC UPDATEUSAGE ('AdventureWorks','Person.Contact') WITH COUNT_ROWS
96. In how many ways you can select distinct records from a table?
97. In how many ways you can select top 1 row?
98. What are the new features introduced in SQL Server 2008 R2?
99. What are the new features added SQL Server 2012 (Denali)?
100. What new feature has been added to TRY-CATCH construct?
… more questions on next post Part-5.
TSQL Interview Questions – Part 3
Next part of TSQL Interview Questions, contd. from my previous post.
51. What are Integrity Constraints?
http://sqlwithmanoj.wordpress.com/2010/11/23/integrity-constraints/
52. Difference between:
- Views, Tables & Stored Procedures
- Stored Procedures & Functions
- Sub Query & Co-related sub-query
- Physical & Logical Schema
- Table variable & Temporary Tables
- UNIQUE and CLUSTERED INDEXES
- Triggers and Constraints
- Primary Key & Unique Key
53. What do you mean by Referential Integrity? How will you attain it?
By using Foreign Keys.
http://www.databasedesign-resource.com/referential-integrity.html
54. What is the sequence for logical query processing, what is the order?
FROM, [JOIN CONDITION, JOIN TABLE ...], ON, OUTER, WHERE, GROUP BY, CUBE/ROLLUP/GROUPING SETS, HAVING, SELECT, DISTINCT, ORDER BY, TOP
http://sqlwithmanoj.wordpress.com/2010/10/28/sql-logical-query-processing-order/
55. How you debug Stored Procedures?
http://support.microsoft.com/kb/316549
http://www.sqlteam.com/article/debugging-stored-procedures-in-visual-studio-2005
http://www.15seconds.com/issue/050106.htm
56. What is ANSI_NULL?
http://sqlwithmanoj.wordpress.com/2010/12/10/set-ansi_nulls-quoted_identifier-ansi_padding/
57. How will you rename a table?
By using sp_rename stored procedure.
58. What are ACID properties, define them?
A – Atomicity (Transaction is atomic, if one part fails, then the entire transaction fails)
C – Consistency (Any transaction the database performs will take it from one consistent state to another, only valid data will be written to the database)
I – Isolation (Other operations cannot access data that has been modified during a transaction that has not yet completed)
D – Durability (On a transaction’s success the transaction will not be lost, the transaction’s data changes will survive system failure, and that all integrity constraints have been satisfied)
More on: http://en.wikipedia.org/wiki/ACID
59. What is a Live Lock?
http://social.msdn.microsoft.com/Forums/en/sqldatabaseengine/thread/478aa50f-b7dd-43fb-bb90-813057a6a1ed
http://blog.sqlauthority.com/2008/03/21/sql-server-introduction-to-live-lock-what-is-live-lock/
60. Difference between “Dirty Read” & “Phantom Read”. Explain both of them?
http://sqlwithmanoj.wordpress.com/2011/07/20/dirty-reads-and-phantom-reads/
61. What is BITMAP index and BITMAP filtering?
http://msdn.microsoft.com/en-us/library/bb522541%28v=SQL.100%29.aspx
http://social.msdn.microsoft.com/Forums/hu-HU/sqldatabaseengine/thread/4717addd-1c8d-4c6b-8607-e191324c1cd8
62. What are different ISOLATION Levels (High to Low)?
http://msdn.microsoft.com/en-us/library/ms189122.aspx
- SERIALIZABLE
- SNAPSHOT
- REPEATABLE READ (phantom read)
- READ COMMITTED
- READ UNCOMMITTED (dirty read)
http://blogs.msdn.com/b/sqlcat/archive/2011/02/20/concurrency-series-basics-of-transaction-isolation-levels.aspx
63. What is the highest, lowest & default ISOLATION Level?
Highest: SERIALIZABLE
Lowest: READ UNCOMMITTED
Default: READ COMMITTED
64. What is SERIALIZABLE Isolation Level?
http://msdn.microsoft.com/en-us/library/ms173763.aspx
65. What is a CTE & how it is different from a Derived table? Example of recursive CTE.
http://sqlwithmanoj.wordpress.com/2011/05/23/cte-recursion-sequence-dates-factorial-fibonacci-series/
66. What are design considerations for a Clustered Index & Non Clustered Index?
67. What are UDFs and their usage in a SELECT query?
- SCALAR
- TABLE VALUED
- MULTI LINE TABLE VALUED
http://sqlwithmanoj.wordpress.com/2010/12/11/udf-user-defined-functions/
68. What are UNION, UNION ALL, EXCEPT & INTERSECTION keywords?
69. What are File Groups in SQL Server? What is its benefit? Explain any scenario where you will use multiple file groups.
http://msdn.microsoft.com/en-us/library/ms179316.aspx
70. How will you handle & avoid Deadlock?
http://www.sql-server-performance.com/tips/deadlocks_p1.aspx
http://support.microsoft.com/kb/169960
http://www.devx.com/getHelpOn/10MinuteSolution/16488/1954
71. What are Implicit Transactions?
http://msdn.microsoft.com/en-us/library/ms188317.aspx
http://msdn.microsoft.com/en-us/library/ms190230.aspx
72. How will you know Index usage on tables?
- Execution plan
- SET STATISTICS PROFILE ON
73. What are Indexed Views and their use? How will you create them?
http://msdn.microsoft.com/en-us/library/ms191432.aspx
A view must meet the following requirements before you can create a clustered index on it:
- The ANSI_NULLS and QUOTED_IDENTIFIER options must have been set to ON when the CREATE VIEW statement was executed.
- The ANSI_NULLS option must have been set to ON for the execution of all CREATE TABLE statements that create tables referenced by the view.
- The view must not reference any other views, only base tables.
- All base tables referenced by the view must be in the same database as the view and have the same owner as the view.
- The view must be created with the SCHEMABINDING option. Schema binding binds the view to the schema of the underlying base tables.
- User-defined functions referenced in the view must have been created with the SCHEMABINDING option.
- Tables and user-defined functions must be referenced by two-part names in the view. One-part, three-part, and four-part names are not allowed.
- If the view definition uses an aggregate function, the SELECT list must also include COUNT_BIG (*).
- If GROUP BY is specified, the view select list must contain a COUNT_BIG(*) expression, and the view definition cannot specify HAVING, ROLLUP, CUBE, or GROUPING SETS.
The SELECT statement in the view cannot contain the following Transact-SQL syntax elements:
- The * or table_name.* syntax to specify columns. Column names must be explicitly stated.
- An expression on a column used in the GROUP BY clause, or an expression on the results of an aggregate.
- A derived table.
- A common table expression (CTE).
- Rowset functions.
- UNION, EXCEPT or INTERSECT operators.
- Subqueries.
- Outer or self joins.
- TOP clause.
- ORDER BY clause.
- DISTINCT keyword.
- COUNT (COUNT_BIG(*) is allowed.)
- A SUM function that references a nullable expression.
- The OVER clause, which includes ranking or aggregate window functions.
- A CLR user-defined aggregate function.
- The full-text predicates CONTAINS or FREETEXT.
- COMPUTE or COMPUTE BY clause.
- The CROSS APPLY or OUTER APPLY operators.
- The PIVOT or UNPIVOT operators
- Table hints (applies to compatibility level of 90 or higher only).
- Join hints.
- Direct references to Xquery expressions. Indirect references, such as Xquery expressions inside a schema-bound user-defined function, are acceptable.
74. What do you mean by Concurrency control?
http://msdn.microsoft.com/en-us/library/ms189130.aspx
75. What do you understand by Star & Snowflake schema and whats the difference between them?
… more questions on next post Part-4.
TSQL Interview Questions – Part 2
Next part of TSQL Interview Questions, contd. from my previous post.
26. What are the virtual tables in Triggers?
Inserted & Deleted
27. What is benefit of a having stored-procedure?
28. Can stored-procedures be recursive? And upto how much level?
Yes, 32 levels.
29. How you can load large data in SQL Server?
BulkCopy is a tool used to copy huge amount of data from tables. BULK INSERT command helps to Imports a data file into a database table or view in a user-specified format.
30. What is the trade-offs of a BCP command, when various users are loading data in a particular table at same time?
31. How can you copy schema from one SQL Server to another?
DTS, import/export wizard.
Scripting out Database objects.
32. What is the benefit of a Temporary Table, how would you define it?
33. What is a table called that has ## before its name, what is its scope?
Table with ## (double pound signs) is called Global Temp table. Scope is outside the session but only till the original session lasts.
34. What is the scope of a temporary table?
Scope is limited to its session only.
35. What is Mutex error in Triggers?
MSDN link: http://social.msdn.microsoft.com/Forums/en-US/transactsql/thread/c86c97a7-73ea-482e-9529-e2407bd7018c
36. What is the use of WITH (nolock)?
Table Hints, MS BOL: http://msdn.microsoft.com/en-us/library/ms187373(v=SQL.90).aspx
http://blogs.msdn.com/b/davidlean/archive/2009/04/06/sql-server-nolock-hint-other-poor-ideas.aspx?wa=wsignin1.0
37. What are the various Isolation levels?
a) Read Uncommitted Isolation Level
b) Read Committed Isolation Level
c) Repeatable Read Isolation Level
d) Serializable Isolation Level
e) Snapshot Isolation Level
f) Read Committed Snapshot Isolation Level
http://www.sql-server-performance.com/articles/dba/isolation_levels_2005_p1.aspx
38. What are implicit & explicit cursors?
http://geekexplains.blogspot.com/2008/11/implicit-vs-explicit-cursors-static-vs.html
39. Define the life cycle of a Cursor.
http://sqlwithmanoj.wordpress.com/2010/10/24/sql-server-cursor-life-cycle/
40. How would you know that if a cursor is open or closed?
declare @mycursor cursor
declare @FirstName varchar(12)
select CURSOR_STATUS('variable','@mycursor') --// -2 (Not applicable)
set @mycursor = cursor for
select FirstName from Person.Contact
select CURSOR_STATUS('variable','@mycursor') --// -1 (The cursor is closed)
open @mycursor
select CURSOR_STATUS('variable','@mycursor') --// 1 (The result set of the cursor has at least one row)
fetch next from @mycursor into @FirstName
select CURSOR_STATUS('variable','@mycursor') --// 1 (The result set of the cursor has at least one row)
close @mycursor
select CURSOR_STATUS('variable','@mycursor') --// -1 (The cursor is closed)
deallocate @mycursor
select CURSOR_STATUS('variable','@mycursor') --// -2 (Not applicable)
select CURSOR_STATUS('variable','@nocursor') --// -3 (A cursor with the specified name does not exist)
41. How many non-clustered indexes can you have in a table?
Upto 249 non-clustered indexes can be created in a table.
42. What all indexes can you have in a table?
One Clustered Index, one or more than one non-clustered index, unique index, filtered, spatial, xml, etc.
MS BOL: http://msdn.microsoft.com/en-us/library/ms175049.aspx
43. How will you know what indexes a particular table is using?
44. What is the benefit of cross joins? How would you use a where clause with Cross Joins?
The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
http://weblogs.sqlteam.com/jeffs/archive/2005/09/12/7755.aspx
http://www.dotnetspider.com/forum/44591-why-we-use-cross-join-sqlserver.aspx
45. Difference between VARCHAR & VARCHAR2?
VARCHAR2 is specific to Oracle. MS SQL Server has VARCHAR & VARCHAR(MAX) data types.
46. What is de-normalization?
De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access. http://social.msdn.microsoft.com/Forums/en-US/transactsql/thread/8c54d1d2-5fbd-4b62-a07f-16c34a863668
47. How would you get error & row number at the same time?
If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it would have been reset.
And if @@Recordcount is checked before the error-checking statement then @@Error would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them in local variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR
http://blog.sqlauthority.com/2007/04/20/sql-server-interview-questions-part-6/
48. What is Collation?
MS BOL link: http://msdn.microsoft.com/en-us/library/aa174903(v=sql.80).aspx
My Blog link: http://sqlwithmanoj.wordpress.com/page/2/?s=collation
49. Types of Replication? Difference between Merge & Transactional Replication.
MS BOL link: http://msdn.microsoft.com/en-us/library/ms165713(v=sql.90).aspx
50. What can you do with COLASCE function?
MS BOL link: http://msdn.microsoft.com/en-us/library/ms190349.aspx
… more questions on next post [Part-3].
2010 in review…
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Crunchy numbers
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Attractions in 2010
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TSQL Interview Questions December 2010
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