Category Archives: SQL Server 2008 R2

Download SQL Server 2008 R2 System Views Map

LOGINPROPERTY Built-In function

SQL Server 2005/2008 built-in function LOGINPROPERTY can help us retrieve the important information of login properties.

We can retrieve the below important details using LOGINPROPERTY function.
1. Date of last password change
2. Login is locked or not
3. Loign password expired
4. Need to change password at next login or not
5. Count of consecutive failed login attempts
6. DateTime when the last login failed
7. DateTime when the login was locked out
8. Password hash
9. Returns the number of days until the password expires. LOGINPROPERTY(‘sa’, ‘DaysUntilExpiration’) argument is only available with SQL Server 2008
SELECT name, CASE LOGINPROPERTY(name, 'IsLocked') WHEN 0 THEN 'No' WHEN 1 THEN 'Yes' ELSE 'Unknown' END as IsAccountLocked, LOGINPROPERTY(name, 'PasswordLastSetTime') as PasswordLastSetDate, LOGINPROPERTY(name, 'BadPasswordCount') as CountOfFailedLoginAttempts, LOGINPROPERTY(name, 'BadPasswordTime') as LastFailedLoginTime, LOGINPROPERTY(name, 'LockoutTime') as LoginLockedOutDateTime, CASE LOGINPROPERTY(name, 'IsExpired') WHEN 0 THEN 'Password is not expired' WHEN 1 THEN 'Password is not expired,change it' ELSE 'Unknown' END as PasswordExpired, CASE LOGINPROPERTY(name, 'IsMustChange') WHEN 0 THEN 'Must not change password at next login' WHEN 1 THEN 'Must change password at next login' ELSE 'Unknown' END as PasswordChangeOnNextLogin, LOGINPROPERTY(name, 'DaysUntilExpiration') as 'DaysUntilthePasswordExpires', --New Property in SQL Server 2008 LOGINPROPERTY(name, 'PasswordHash') as PasswordHash From sys.sql_logins order by name

Output

SQL Server 2008 R2 Editions and Key Features

SQL Server 2005 Interview Questions

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Download SQL Server Interview Question

• If I want to see what fields a table is made of, and what the sizes of the
fields are, what option do I have to look for?
Sp_Columns ‘TableName’

• What is a query?
A request for information from a database. There are three general methods for posing queries:
# Choosing parameters from a menu: In this method, the database system presents a list of parameters from which you can choose. This is perhaps the easiest way to pose a query because the menus guide you, but it is also the least flexible.
# Query by example (QBE): In this method, the system presents a blank record and lets you specify the fields and values that define the query.
# Query language: Many database systems require you to make requests for information in the form of a stylized query that must be written in a special query language. This is the most complex method because it forces you to learn a specialized language, but it is also the most powerful.

• What is the purpose of the model database?
It works as Template Database for the Create Database Syntax

• What is the purpose of the master database?
Master database keeps the information about sql server configuration, databases users etc

• What is the purpose of the tempdb database?
Tempdb database keeps the information about the temporary objects (#TableName, #Procedure). Also the sorting, DBCC operations are performed in the TempDB

• What is the purpose of the USE command?
Use command is used for to select the database. For i.e Use Database Name

• If you delete a table in the database, will the data in the table be deleted too?
Yes

• What is the Parse Query button used for? How does this help you?
Parse query button is used to check the SQL Query Syntax

• Tables are created in a ____________________ in SQL Server 2005.
resouce database(System Tables)

• What is usually the first word in a SQL query?
SELECT

• Does a SQL Server 2005 SELECT statement require a FROM?
NO

• Can a SELECT statement in SQL Server 2005 be used to make an assignment? Explain with examples.
Yes. Select @MyDate = GetDate()

• What is the ORDER BY used for?
Order By clause is used for sorting records in Ascending or Descending order

• Does ORDER BY actually change the order of the data in the tables or does it just
change the output?
Order By clause change only the output of the data

• What is the default order of an ORDER BY clause?
Ascending Order

• What kind of comparison operators can be used in a WHERE clause?

Operator	Meaning
= (Equals)	Equal to
> (Greater Than)	Greater than
< (Less Than)	Less than
>= (Greater Than or Equal To)	Greater than or equal to
<= (Less Than or Equal To)	Less than or equal to
<> (Not Equal To)	Not equal to
!= (Not Equal To)	Not equal to (not SQL-92 standard)
!< (Not Less Than)	Not less than (not SQL-92 standard)
!> (Not Greater Than)	Not greater than (not SQL-92 standard)

• What are four major operators that can be used to combine conditions on a WHERE
clause?

OR, AND, IN and BETWEEN

• What are the logical operators?

Operator	Meaning
ALL	TRUE if all of a set of comparisons are TRUE.
AND	TRUE if both Boolean expressions are TRUE.
ANY	TRUE if any one of a set of comparisons are TRUE.
BETWEEN	TRUE if the operand is within a range.
EXISTS	TRUE if a subquery contains any rows.
IN	TRUE if the operand is equal to one of a list of expressions.
LIKE	TRUE if the operand matches a pattern.
NOT	Reverses the value of any other Boolean operator.
OR	TRUE if either Boolean expression is TRUE.
SOME	TRUE if some of a set of comparisons are TRUE.

•In a WHERE clause, do you need to enclose a text column in quotes? Do you need to enclose a numeric column in quotes?
Enclose Text in Quotes (Yes)
Enclose Number in Quotes (NO)

• Is a null value equal to anything? Can a space in a column be considered a null value? Why or why not?
No NULL value means nothing. We can’t consider space as NULL value.

• Will COUNT(column) include columns with null values in its count?
Yes, it will include the null column in count

• What are column aliases? Why would you want to use column aliases? How can you embed blanks in column aliases?
You can create aliases for column names to make it easier to work with column names, calculations, and summary values. For example, you can create a column alias to:
* Create a column name, such as “Total Amount,” for an expression such as (quantity * unit_price) or for an aggregate function.
* Create a shortened form of a column name, such as “d_id” for “discounts.stor_id.”
After you have defined a column alias, you can use the alias in a Select query to specify query output

• What are table aliases?
Aliases can make it easier to work with table names. Using aliases is helpful when:
* You want to make the statement in the SQL Pane shorter and easier to read.
* You refer to the table name often in your query — such as in qualifying column names — and want to be sure you stay within a specific character-length limit for your query. (Some databases impose a maximum

length for queries.)
* You are working with multiple instances of the same table (such as in a self-join) and need a way to refer to one instance or the other.

• What are table qualifiers? When should table qualifiers be used?
[@table_qualifier =] qualifier
Is the name of the table or view qualifier. qualifier is sysname, with a default of NULL. Various DBMS products support three-part naming for tables (qualifier.owner.name). In SQL Server, this column represents the database name. In some products, it represents the server name of the table’s database environment.

• Are semicolons required at the end of SQL statements in SQL Server 2005?
No it is not required

• Do comments need to go in a special place in SQL Server 2005?
No its not necessary

• When would you use the ROWCOUNT function versus using the WHERE clause?
Returns the number of rows affected by the last statement. If the number of rows is more than 2 billion, use ROWCOUNT_BIG.
Transact-SQL statements can set the value in @@ROWCOUNT in the following ways:
* Set @@ROWCOUNT to the number of rows affected or read. Rows may or may not be sent to the client.
* Preserve @@ROWCOUNT from the previous statement execution.
* Reset @@ROWCOUNT to 0 but do not return the value to the client.
Statements that make a simple assignment always set the @@ROWCOUNT value to 1.

• Is SQL case-sensitive? Is SQL Server 2005 case-sensitive?
No both are not case-sensitive. Case sensitivity depends on the collation you choose.
If you installed SQL Server with the default collation options, you might find that the following queries return the same results:

CREATE TABLE mytable
(
mycolumn VARCHAR(10)
)
GO

SET NOCOUNT ON

INSERT mytable VALUES(‘Case’)
GO

SELECT mycolumn FROM mytable WHERE mycolumn=’Case’
SELECT mycolumn FROM mytable WHERE mycolumn=’caSE’
SELECT mycolumn FROM mytable WHERE mycolumn=’case’

You can alter your query by forcing collation at the column level:

SELECT myColumn FROM myTable
WHERE myColumn COLLATE Latin1_General_CS_AS = ‘caSE’

SELECT myColumn FROM myTable
WHERE myColumn COLLATE Latin1_General_CS_AS = ‘case’

SELECT myColumn FROM myTable
WHERE myColumn COLLATE Latin1_General_CS_AS = ‘Case’

— if myColumn has an index, you will likely benefit by adding
— AND myColumn = ‘case’

• What is a synonym? Why would you want to create a synonym?
SYNONYM is a single-part name that can replace a two, three or four-part name in many SQL statements. Using SYNONYMS in RDBMS cuts down on typing.
SYNONYMs can be created for the following objects:

* Table
* View
* Assembly (CLR) Stored Procedure
* Assembly (CLR) Table-valued Function
* Assembly (CLR) Scalar Function
* Assembly Aggregate (CLR) Aggregate Functions
* Replication-filter-procedure
* Extended Stored Procedure
* SQL Scalar Function
* SQL Table-valued Function
* SQL Inline-table-valued Function
* SQL Stored Procedure

Syntax
CREATE SYNONYM [ schema_name_1. ] synonym_name FOR < object >

< object > :: =
{
[ server_name.[ database_name ] . [ schema_name_2 ].| database_name . [ schema_name_2 ].| schema_name_2. ] object_name
}

• Can a synonym name of a table be used instead of a table name in a SELECT statement?
Yes

• Can a synonym of a table be used when you are trying to alter the definition of a table?
Not Sure will try

• Can you type more than one query in the query editor screen at the same time?
Yes we can.

• While you are inserting values into a table with the INSERT INTO .. VALUES option, does the order of the columns in the INSERT statement have to be the same as the order of the columns in the table?
Not Necessary

• While you are inserting values into a table with the INSERT INTO .. SELECT option, does the order of the columns in the INSERT statement have to be the same as the order of the columns in the table?
Yes if you are not specifying the column names in the insert clause, you need to maintain the column order in SELECT statement

• When would you use an INSERT INTO .. SELECT option versus an INSERT INTO .. VALUES option? Give an example of each.
INSERT INTO .. SELECT is used insert data in to table from diffrent tables or condition based insert
INSERT INTO .. VALUES you have to specify the insert values

• What does the UPDATE command do?
Update command will modify the existing record

• Can you change the data type of a column in a table after the table has been created? If so,which command would you use?
Yes we can. Alter Table Modify Column

• Will SQL Server 2005 allow you to reduce the size of a column?
Yes it allows

• What integer data types are available in SQL Server 2005?

Exact-number data types that use integer data.

Data type	Range	Storage
bigint	-2^63 (-9,223,372,036,854,775,808) to 2^63-1 (9,223,372,036,854,775,807)	8 Bytes
int	-2^31 (-2,147,483,648) to 2^31-1 (2,147,483,647)	4 Bytes
smallint	-2^15 (-32,768) to 2^15-1 (32,767)	2 Bytes
tinyint	0 to 255	1 Byte

• What is the default value of an integer data type in SQL Server 2005?
NULL

• What is the difference between a CHAR and a VARCHAR datatype?

CHAR and VARCHAR data types are both non-Unicode character data types with a maximum length of 8,000 characters. The main difference between these 2 data types is that a CHAR data type is fixed-length while a VARCHAR is variable-length. If the number of characters entered in a CHAR data type column is less than the declared column length, spaces are appended to it to fill up the whole length.

Another difference is in the storage size wherein the storage size for CHAR is n bytes while for VARCHAR is the actual length in bytes of the data entered (and not n bytes).

You should use CHAR data type when the data values in a column are expected to be consistently close to the same size. On the other hand, you should use VARCHAR when the data values in a column are expected to vary considerably in size.

• Does Server SQL treat CHAR as a variable-length or fixed-length column?
SQL Server treats CHAR as fixed length column

• If you are going to have too many nulls in a column, what would be the best data type to use?
Variable length columns only use a very small amount of space to store a NULL so VARCHAR datatype is the good option for null values

• When columns are added to existing tables, what do they initially contain?
The column initially contains the NULL values

• What command would you use to add a column to a table in SQL Server?
ALTER TABLE tablename ADD column_name DATATYPE

• Does an index slow down updates on indexed columns?
Yes

• What is a constraint?
Constraints in Microsoft SQL Server 2000/2005 allow us to define the ways in which we can automatically enforce the integrity of a database. Constraints define rules regarding permissible values allowed in columns and are the standard mechanism for enforcing integrity. Using constraints is preferred to using triggers, stored procedures, rules, and defaults, as a method of implementing data integrity rules. The query optimizer also uses constraint definitions to build high-performance query execution plans.

• How many indexes does SQL Server 2005 allow you to have on a table?
250 indices per table

• What command would you use to create an index?
CREAT INDEX INDEXNAME ON TABLE(COLUMN NAME)

• What is the default ordering that will be created by an index (ascending or descending)?
Clustered indexes can be created in SQL Server databases. In such cases the logical order of the index key values will be the same as the physical order of rows in the table.
By default it is ascending order, we can also specify the index order while index creation.
CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name
ON { table | view } ( column [ ASC | DESC ] [ ,…n ] )

• How do you delete an index?
DROP INDEX authors.au_id_ind

• What does the NOT NULL constraint do?
Constrain will not allow NULL values in the column

• What command must you use to include the NOT NULL constraint after a table has already been created?
DEFAULT, WITH CHECK or WITH NOCHECK

• When a PRIMARY KEY constraint is included in a table, what other constraints does this imply?
Unique + NOT NULL

• What is a concatenated primary key?
Each table has one and only one primary key, which can consist of one or many columns. A concatenated primary key comprises two or more columns. In a single table, you might find several columns, or groups of columns, that might serve as a primary key and are called candidate keys. A table can have more than one candidate key, but only one candidate key can become the primary key for that table

• How are the UNIQUE and PRIMARY KEY constraints different?
A UNIQUE constraint is similar to PRIMARY key, but you can have more than one UNIQUE constraint per table.

When you declare a UNIQUE constraint, SQL Server creates a UNIQUE index to speed up the process of searching for duplicates. In this case the index defaults to NONCLUSTERED index, because you can have only one CLUSTERED index per table.

* The number of UNIQUE constraints per table is limited by the number of indexes on the table i.e 249 NONCLUSTERED index and one possible CLUSTERED index.

Contrary to PRIMARY key UNIQUE constraints can accept NULL but just once. If the constraint is defined in a combination of fields, then every field can accept NULL and can have some values on them, as long as the combination values is unique.

• What is a referential integrity constraint? What two keys does the referential integrity constraint usually include?
Referential integrity in a relational database is consistency between coupled tables. Referential integrity is usually enforced by the combination of a primary key or candidate key (alternate key) and a foreign key. For referential integrity to hold, any field in a table that is declared a foreign key can contain only values from a parent table’s primary key or a candidate key. For instance, deleting a record that contains a value referred to by a foreign key in another table would break referential integrity. The relational database management system (RDBMS) enforces referential integrity, normally either by deleting the foreign key rows as well to maintain integrity, or by returning an error and not performing the delete. Which method is used would be determined by the referential integrity constraint, as defined in the data dictionary.

• What is a foreign key?
FOREIGN KEY constraints identify the relationships between tables.
A foreign key in one table points to a candidate key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no candidate keys with that value. In the following sample, the order_part table establishes a foreign key referencing the part_sample table defined earlier. Usually, order_part would also have a foreign key against an order table, but this is a simple example.

CREATE TABLE order_part
(order_nmbr int,
part_nmbr int
FOREIGN KEY REFERENCES part_sample(part_nmbr)
ON DELETE NO ACTION,
qty_ordered int)
GO

You cannot insert a row with a foreign key value (except NULL) if there is no candidate key with that value. The ON DELETE clause controls what actions are taken if you attempt to delete a row to which existing foreign keys point. The ON DELETE clause has two options:

NO ACTION specifies that the deletion fails with an error.

CASCADE specifies that all the rows with foreign keys pointing to the deleted row are also deleted.
The ON UPDATE clause defines the actions that are taken if you attempt to update a candidate key value to which existing foreign keys point. It also supports the NO ACTION and CASCADE options.

• What does the ON DELETE CASCADE option do?
ON DELETE CASCADE
Specifies that if an attempt is made to delete a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are also deleted. If cascading referential actions have also been defined on the target tables, the specified cascading actions are also taken for the rows deleted from those tables.

ON UPDATE CASCADE
Specifies that if an attempt is made to update a key value in a row, where the key value is referenced by foreign keys in existing rows in other tables, all of the foreign key values are also updated to the new value specified for the key. If cascading referential actions have also been defined on the target tables, the specified cascading actions are also taken for the key values updated in those tables.

• What does the ON UPDATE NO ACTION do?
ON DELETE NO ACTION
Specifies that if an attempt is made to delete a row with a key referenced by foreign keys in existing rows in other tables, an error is raised and the DELETE is rolled back.

ON UPDATE NO ACTION
Specifies that if an attempt is made to update a key value in a row whose key is referenced by foreign keys in existing rows in other tables, an error is raised and the UPDATE is rolled back.

• Can you use the ON DELETE and ON UPDATE in the same constraint?
Yes we can.
CREATE TABLE part_sample
(part_nmbr int PRIMARY KEY,
part_name char(30),
part_weight decimal(6,2),
part_color char(15) )

CREATE TABLE order_part
(order_nmbr int,
part_nmbr int
FOREIGN KEY REFERENCES part_sample(part_nmbr)
ON DELETE NO ACTION ON UPDATE NO ACTION,
qty_ordered int)
GO

Download SQL Server Interview Question

Transactions and Locks in SQL Server

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• What is a “Database Transactions “?
A database transaction is a unit of work performed against a database management system or similar system that is treated in a coherent and reliable way independent of other transactions. A database transaction, by definition, must be atomic, consistent, isolated and durable. These properties of database transactions are often referred to by the acronym ACID.

Transactions provide an “all-or-nothing” proposition stating that work units performed in a database must be completed in their entirety or take no effect whatsoever. Further, transactions must be isolated from other transactions, results must conform to existing constraints in the database and transactions that complete successfully must be committed to durable storage.

In some systems, transactions are also called LUWs for Logical Units of Work.

• What is ACID?
The ACID model is one of the oldest and most important concepts of database theory. It sets forward four goals that every database management system must strive to achieve: atomicity, consistency, isolation and durability. No database that fails to meet any of these four goals can be considered reliable.

Let’s take a moment to examine each one of these characteristics in detail:

Atomicity states that database modifications must follow an “all or nothing” rule. Each transaction is said to be “atomic.” If one part of the transaction fails, the entire transaction fails. It is critical that the database management system maintain the atomic nature of transactions in spite of any DBMS, operating system or hardware failure.

Consistency states that only valid data will be written to the database.If, for some reason, a transaction is executed that violates the database’s consistency rules, the entire transaction will be rolled back and the database will be restored to a state consistent with those rules. On the other hand, if a transaction successfully executes, it will take the database from one state that is consistent with the rules to another state that is also consistent with the rules.

Isolation requires that multiple transactions occurring at the same time not impact each other’s execution. For example, if Joe issues a transaction against a database at the same time that Mary issues a different transaction, both transactions should operate on the database in an isolated manner. The database should either perform Joe’s entire transaction before executing Mary’s or vice-versa. This prevents Joe’s transaction from reading intermediate data produced as a side effect of part of Mary’s transaction that will not eventually be committed to the database. Note that the isolation property does not ensure which transaction will execute first, merely that they will not interfere with each other.

Durability ensures that any transaction committed to the database will not be lost. Durability is ensured through the use of database backups and transaction logs that facilitate the restoration of committed transactions in spite of any subsequent software or hardware failures.

• What is “Begin Trans”, “Commit Tran”, “Rollback Tran” and “Save Tran”?
Transactions group a set of tasks into a single execution unit. Each transaction begins with a specific task and ends when all the tasks in the group successfully complete. If any of the tasks fails, the transaction fails. Therefore, a transaction has only two results: success or failure. Incomplete steps result in the failure of the transaction.

Users can group two or more Transact-SQL statements into a single transaction using the following statements:

* Begin Transaction
* Rollback Transaction
* Commit Transaction

Begin Transaction
Marks the starting point of an explicit, local transaction. BEGIN TRANSACTION increments @@TRANCOUNT by 1.

Rollback Transaction
If anything goes wrong with any of the grouped statements, all changes need to be aborted. The process of reversing changes is called rollback in SQL Server terminology.
A ROLLBACK, on the other hand, works regardless of the level at which it is issued, but rolls back all transactions, regardless of the nesting level

Commit Transaction
If everything is in order with all statements within a single transaction, all changes are recorded together in the database. In SQL Server terminology, we say that these changes are committed to the database.
A COMMIT issued against any transaction except the outermost one doesn’t commit any changes to disk – it merely decrements the@@TRANCOUNT automatic variable.

Save Tran
Savepoints offer a mechanism to roll back portions of transactions. A user can set a savepoint, or marker, within a transaction. The savepoint defines a location to which a transaction can return if part of the transaction is conditionally canceled. SQL Server allows you to use savepoints via the SAVE TRAN statement, which doesn’t affect the @@TRANCOUNT value. A rollback to a savepoint (not a transaction) doesn’t affect the value returned by @@TRANCOUNT, either. However, the rollback must explicitly name the savepoint: using ROLLBACK TRAN without a specific name will always roll back the entire transaction.

• What are “Checkpoint’s” in SQL Server?
Forces all dirty pages for the current database to be written to disk. Dirty pages are data or log pages modified after entered into the buffer cache, but the modifications have not yet been written to disk.

Syntax
CHECKPOINT

• What are “Implicit Transactions”?
Microsoft SQL Server operates in three transaction modes:
Autocommit transactions
Each individual statement is a transaction.
Explicit transactions
Each transaction is explicitly started with the BEGIN TRANSACTION statement and explicitly ended with a COMMIT or ROLLBACK statement.
Implicit transactions
A new transaction is implicitly started when the prior transaction completes, but each transaction is explicitly completed with a COMMIT or ROLLBACK statement.

• Is it good to use “Implicit Transactions”?
If you want all your commands to require an explicit COMMIT or ROLLBACK in order to finish, you can issue the command SET IMPLICIT_TRANSACTIONS ON. By default, SQL Server operates in the autocommit mode; it does not operate with implicit transactions. Any time you issue a data modification command such as INSERT, UPDATE, or DELETE, SQL Server automatically commits the transaction. However, if you use the SET IMPLICIT_TRANSACTIONS ON command, you can override the automatic commitment so that SQL Server will wait for you to issue an explicit COMMIT or ROLLBACK statement to do anything with the transaction. This can be handy when you issue commands interactively, mimicking the behavior of other databases such as Oracle.

What’s distinctive about implicit transactions is that reissuing SET IMPLICIT_TRANSACTIONS ON does not increase the value of @@TRANCOUNT. Also, neither COMMIT nor ROLLBACK reduce the value of @@TRANCOUNT until after you issue the command SET IMPLICIT_TRANSACTIONS OFF. Developers do not often use implicit transactions; however, there is an interesting exception in ADO. See the sidebar, Implicit Transactions and ADO Classic.

• What is Concurrency?
When many people attempt to modify data in a database at the same time, a system of controls must be implemented so that modifications made by one person do not adversely affect those of another person. This is called concurrency control.

Concurrency control theory has two classifications for the methods of instituting concurrency control:
Pessimistic concurrency control
A system of locks prevents users from modifying data in a way that affects other users. After a user performs an action that causes a lock to be applied, other users cannot perform actions that would conflict with the lock until the owner releases it. This is called pessimistic control because it is mainly used in environments where there is high contention for data, where the cost of protecting data with locks is less than the cost of rolling back transactions if concurrency conflicts occur.
Optimistic concurrency control
In optimistic concurrency control, users do not lock data when they read it. When an update is performed, the system checks to see if another user changed the data after it was read. If another user updated the data, an error is raised. Typically, the user receiving the error rolls back the transaction and starts over. This is called optimistic because it is mainly used in environments where there is low contention for data, and where the cost of occasionally rolling back a transaction outweighs the costs of locking data when read.

• What are “Dirty reads”?
Uncommitted dependency occurs when a second transaction selects a row that is being updated by another transaction. The second transaction is reading data that has not been committed yet and may be changed by the transaction updating the row.

• What are “Unrepeatable reads”?
Inconsistent Analysis (Nonrepeatable Read)
Inconsistent analysis occurs when a second transaction accesses the same row several times and reads different data each time. Inconsistent analysis is similar to uncommitted dependency in that another transaction is changing the data that a second transaction is reading. However, in inconsistent analysis, the data read by the second transaction was committed by the transaction that made the change. Also, inconsistent analysis involves multiple reads (two or more) of the same row and each time the information is changed by another transaction; thus, the term nonrepeatable read.

• What are “Phantom rows”?
Phantom reads occur when an insert or delete action is performed against a row that belongs to a range of rows being read by a transaction. The transaction’s first read of the range of rows shows a row that no longer exists in the second or succeeding read, as a result of a deletion by a different transaction. Similarly, as the result of an insert by a different transaction, the transaction’s second or succeeding read shows a row that did not exist in the original read.

For example, an editor makes changes to a document submitted by a writer, but when the changes are incorporated into the master copy of the document by the production department, they find that new unedited material has been added to the document by the author. This problem could be avoided if no one could add new material to the document until the editor and production department finish working with the original document.

• What are “Lost Updates”?
Lost updates occur when two or more transactions select the same row and then update the row based on the value originally selected. Each transaction is unaware of other transactions. The last update overwrites updates made by the other transactions, which results in lost data.

• What are different levels of granularity of locking resources?
Microsoft SQL Server 2000 has multigranular locking that allows different types of resources to be locked by a transaction. To minimize the cost of locking, SQL Server locks resources automatically at a level appropriate to the task. Locking at a smaller granularity, such as rows, increases concurrency, but has a higher overhead because more locks must be held if many rows are locked. Locking at a larger granularity, such as tables, are expensive in terms of concurrency because locking an entire table restricts access to any part of the table by other transactions, but has a lower overhead because fewer locks are being maintained.

SQL Server can lock these resources (listed in order of increasing granularity).
RID: Row identifier. Used to lock a single row within a table.
Key: Row lock within an index. Used to protect key ranges in serializable transactions.
Page: 8 kilobyte –(KB) data page or index page.
Extent: Contiguous group of eight data pages or index pages.
Table: Entire table, including all data and indexes.
DB: Database.

• What are different types of Isolation levels in SQL Server?
READ COMMITTED
Specifies that shared locks are held while the data is being read to avoid dirty reads, but the data can be changed before the end of the transaction, resulting in nonrepeatable reads or phantom data. This option is the SQL Server default.

READ UNCOMMITTED
Implements dirty read, or isolation level 0 locking, which means that no shared locks are issued and no exclusive locks are honored. When this option is set, it is possible to read uncommitted or dirty data; values in the data can be changed and rows can appear or disappear in the data set before the end of the transaction. This option has the same effect as setting NOLOCK on all tables in all SELECT statements in a transaction. This is the least restrictive of the four isolation levels.

REPEATABLE READ
Locks are placed on all data that is used in a query, preventing other users from updating the data, but new phantom rows can be inserted into the data set by another user and are included in later reads in the current transaction. Because concurrency is lower than the default isolation level, use this option only when necessary.

SERIALIZABLE
Places a range lock on the data set, preventing other users from updating or inserting rows into the data set until the transaction is complete. This is the most restrictive of the four isolation levels. Because concurrency is lower, use this option only when necessary. This option has the same effect as setting HOLDLOCK on all tables in all SELECT statements in a transaction.

• If you are using COM+, what “Isolation” level is set by default?
SERIALIZABLE transaction isolation level is the default isolation level for the COM+ application.

• What are “Lock” hints?
A range of table-level locking hints can be specified using the SELECT, INSERT, UPDATE, and DELETE statements to direct Microsoft SQL Server 2000 to the type of locks to be used. Table-level locking hints can be used when a finer control of the types of locks acquired on an object is required. These locking hints override the current transaction isolation level for the session.

• What is a “Deadlock”?
Deadlocking occurs when two user processes have locks on separate objects and each process is trying to acquire a lock on the object that the other process has. When this happens, SQL Server identifies the problem and ends the deadlock by automatically choosing one process and aborting the other process, allowing the other process to continue. The aborted transaction is rolled back and an error message is sent to the user of the aborted process. Generally, the transaction that requires the least amount of overhead to rollback is the transaction that is aborted.

• What are the steps you can take to avoid “Deadlocks”?
Here are some tips on how to avoid deadlocking on your SQL Server:
* Ensure the database design is properly normalized.
* Have the application access server objects in the same order each time.
* During transactions, don’t allow any user input. Collect it before the transaction begins.
* Avoid cursors.
* Keep transactions as short as possible. One way to help accomplish this is to reduce the number of round trips between your application and SQL Server by using stored procedures or keeping transactions with a single batch. Another way of reducing the time a transaction takes to complete is to make sure you are not performing the same reads over and over again. If your application does need to read the same data more than once, cache it by storing it in a variable or an array, and then re-reading it from there, not from SQL Server.
* Reduce lock time. Try to develop your application so that it grabs locks at the latest possible time, and then releases them at the very earliest time.
* If appropriate, reduce lock escalation by using the ROWLOCK or PAGLOCK.
* Consider using the NOLOCK hint to prevent locking if the data being locked is not modified often.
* If appropriate, use as low of an isolation level as possible for the user connection running the transaction.
* Consider using bound connections.

• What is Bound Connection?
Bound connections allow two or more connections to share the same transaction and locks. Bound connections can work on the same data without lock conflicts. Bound connections can be created from multiple connections within the same application, or from multiple applications with separate connections. Bound connections make coordinating actions across multiple connections easier.

To participate in a bound connection, a connection calls sp_getbindtoken or srv_getbindtoken (Open Data Services) to get a bind token. A bind token is a character string that uniquely identifies each bound transaction. The bind token is then sent to the other connections participating in the bound connection. The other connections bind to the transaction by calling sp_bindsession, using the bind token received from the first connection.

• Specity the types of Bound Connections
Local bound connection
Allows bound connections to share the transaction space of a single transaction on a single server.
Distributed bound connection
Allows bound connections to share the same transaction across two or more servers until the entire transaction is either committed or rolled back by using Microsoft Distributed Transaction Coordinator (MS DTC).

• How can I know what locks are running on which resource?
Use SP_Locks system stored procedure

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