Tag Archives: SQL Server Interivew Questions

SQL Server Interview Questions 2K9 – Part – I

Question: What is COMMIT & ROLLBACK statement in SQL ?
Answer:
Commit statement helps in termination of the current transaction and does all the changes that occur in transaction persistent and this also commits all the changes to the database. COMMIT we can also use in store procedure.
ROLLBACK do the same thing just terminate the current transaction but one another thing is that the changes made to database are ROLLBACK to the database.

Question:-What is difference between OSQL and Query Analyzer ?
Answer:-Both are the same but there is little difference OSQL is command line tool which is execute query and display the result same a query analyzer but query analyzer is graphical and OSQL is a command line tool.OSQL have not ability like query analyzer to analyze queries and show static on speed of execution and other useful thing about OSQL is that its helps in scheduling.

Question: What is SQL?

Answer: The Structured Query Language (SQL) is foundation for all relational database systems. Most of the large-scale databases use the SQL to define all user and administrator interactions. QL is Non-Procedural language. It allows the user to concentrate on specifying what data is required rather than concentrating on the how to get it.

 

The DML component of SQL comprises four basic statements:
* SELECT
to get rows from tables
* UPDATE
to update the rows of tables
* DELETE
to remove rows from tables
* INSERT
to add new rows to tables

Question: What is DTS in SQL Server?
Answer:
If a organization is big then it is also there that there is multiple option to store data some people are using EXCEL some are using ACCESS and some of they are using SQL SERVER and in some other format also but there a problem is arise that how to merge that data into one format there is different tool are there for doing this function. One of product of SQL SERVER-2000 DTS helps in this problem it provides a set of tool from that tool we can customize are database according to our need DTSRun is a command-prompt utility used to execute existing DTS packages.

Question: What is the difference between SQL and Pl/Sql?
Answer:
We can get modify, Retrieve by single command or statement in SQL but PL/SQL process all SQL statements one at a time. With PL/SQL, an entire block of statements process in a single command line. sql is structured query language ,various queries are used to handle the database in a simplified manner. While pl/sql is procedural language contains various types of variable, functions and procedures and other major difference is Sql as the name suggest it is just structured query language whereas PLSQL is a combination of Programming language & SQL.

Question: Can You explain integration between SQL Server 2005 and Visual Studio 2005?
Answer:
This integration provide wider range of development with the help of CLR for database server. Because CLR helps developers to get flexibility for developing database applications and also provides language interoperability just like Visual C++, Visual Basic .Net and Visual C# .Net. The CLR helps developers to get the arrays, classes and exception handling available through programming languages such as Visual C++ or Visual C# which is use in stored procedures, functions and triggers for creating database application dynamically and also provide more efficient reuse of code and faster execution of complex tasks. We particularly liked the error-checking powers of the CLR environment, which reduces run-time errors

Question: What are Checkpoint in SQL Server?
Answer:
When we done operation on SQL SERVER that is not committed directly to the database. All operation must be logged in to Transaction Log files after that they should be done on to the main database. Checkpoint are the point which alert Sql Server to save all the data to main database if no check point is there then log files get full we can use Checkpoint command to commit all data in the SQL SERVER. When we stop the SQL Server it will take long time because Checkpoint is also fired.

Question: What is the difference between UNION ALL Statement and UNION?
Answer:-
The main difference between UNION ALL statement and UNION is UNION All statement is much faster than UNION, the reason behind this is that because UNION ALL statement does not look for duplicate rows, but on the other hand UNION statement does look for duplicate rows, whether or not they exist.

Question: Write some disadvantage of Cursor?
Answer:-
Cursor plays there row quite nicely but although there are some disadvantage of Cursor .
Because we know cursor doing roundtrip it will make network line busy and also make time consuming methods. First of all select query gernate output and after that cursor goes one by one so roundtrip happen.Another disadvange of cursor are ther are too costly because they require lot of resources and temporary storage so network is quite busy.

Question: What is Log Shipping and its purpose?
Answer:
In Log Shipping the transactional log file from one server is automatically updated in backup database on the other server and in the case when one server fails the other server will have the same DB and we can use this as the DDR(disaster recovery) plan.

Question: What are the null values in SQL SERVER?
Answer:
Before understand the null values we have some overview about what the value is. Value is the actual data stored in a particular field of particular record. But what is done when there is no value in the field. That value is something like <null>.Nulls present missing information. We can also call null propagation.

Question: What is difference between OSQL and Query Analyzer?
Answer:
Both are same for functioning but there is a little difference OSQL is command line tool which execute query and display the result same a Query Analyzer do but Query Analyzer is graphical.OSQL have not ability like Query Analyzer to analyze queries and show statistics on speed of execution .And other useful thing about OSQL is that its helps in scheduling which is done in Query Analyzer with the help of JOB.

 

Question: Write a Role of Sql Server 2005 in XML Web Services?
Answer:-
SQL Server 2005 create a standard method for getting the database engine using SOAP via HTTP. By this method, we can send SOAP/HTTP requests to SQL Server for executing T-SQL batch statements, stored procedures, extended stored procedures, and scalar-valued user-defined functions may be with or without parameters.

Question: What are the different types of Locks ?
Answer:
There are three main types of locks that SQL Server
(1)Shared locks are used for operations that does not allow to change or update data, such as a SELECT statement.
(2)Update locks are used when SQL Server intends to modify a page, and later promotes the update page lock to an exclusive page lock before actually making the changes.
(3)Exclusive locks are used for the data modification operations, such as UPDATE, INSERT, or DELETE.

Question: What is ‘Write-ahead log’ in Sql Server 2000?
Answer:
Before understanding it we must have an idea about the transaction log files. These files are the files which hold the data for change in database.
Now we explain when we are doing some Sql Server 2000 query or any Sql query like Sql insert query, delete sql query, update sql query and change the data in sql server database it cannot change the database directly to table .Sql server extracts the data that is modified by sql server 2000 query or by sql query and places it in memory. Once data is stores in memory user can make changes to that a log file is generated this log file is generated in every five minutes of transaction is done. After this sql server writes changes to database with the help of transaction log files. This is called Write-ahead log.

Question: What do u mean by Extents and types of Extents ?
Answer:
An Extent is a collection of 8 sequential pages to hold database from becoming fragmented. Fragment means these pages relates to same table of database these also holds in indexing. To avoid for fragmentation Sql Server assign space to table in extents. So that the Sql Server keep up to date data in extents. Because these pages are continuously one after another. There are usually two types of extends:-Uniform and Mixed.
Uniform means when extent is own by a single object means all collection of 8 ages hold by a single extent is called uniform.
Mixed mean when more then one object is comes in extents is known as mixed extents.

Question: What is different in Rules and Constraints?
Answer:
Rules and Constraints are similar in functionality but there is little difference between them. Rules are used for backward compatibility. One the most exclusive difference is that we can bind rules to a data types whereas constraints are bound only to columns. So we can create our own data type with the help of Rules and get the input according to that.

Question: What Is Database?
Answer:
A database is similar to a data file in that it is a storage place for data. Like a data file, a database does not present information directly to a user; the user runs an application that accesses data from the database and presents it to the user in an understandable format. Database systems are more powerful than data files in that data is more highly organized. In a well-designed database, there are no duplicate pieces of data that the user or application must update at the same time. Related pieces of data are grouped together in a single structure or record, and relationships can be defined between these structures and records. When working with data files, an application must be coded to work with the specific structure of each data file. In contrast, a database contains a catalog that applications use to determine how data is organized. Generic database applications can use the catalog to present users with data from different databases dynamically, without being tied to a specific data format. A database typically has two main parts: first, the files holding the physical database and second, the database management system (DBMS) software that applications use to access data. The DBMS is responsible for enforcing the database structure, including: · maintaining relationships between data in the database. Ensuring that data is stored correctly and that the rules defining data relationships are not violated. · Recovering all data to a point of known consistency in case of system failures.

Question: what is Relational Database?
Answer: Although there are different ways to organize data in a database, relational databases are one of the most effective. Relational database systems are an application of mathematical set theory to the problem of effectively organizing data. In a relational database, data is collected into tables (called relations in relational theory). A table represents some class of objects that are important to an organization. For example, a company may have a database with a table for employees, another table for customers, and another for stores. Each table is built of columns and rows (called attributes and tuples in relational theory). Each column represents some attribute of the object represented by the table. For example, an Employee table would typically have columns for attributes such as first name, last name, employee ID, department, pay grade, and job title. Each row represents an instance of the object represented by the table. For example, one row in the Employee table represents the employee who has employee ID 12345. When organizing data into tables, you can usually find many different ways to define tables. Relational database theory defines a process called normalization, which ensures that the set of tables you define will organize your data effectively.

Question: What are Data Integrity and its categories?
Answer:
Enforcing data integrity ensures the quality of the data in the database. For example, if an employee is entered with an employee_id value of 123, the database should not allow another employee to have an ID with the same value. If you have an employee_rating column intended to have values ranging from 1 to 5, the database should not accept a value of 6. If the table has a dept_id column that stores the department number for the employee, the database should allow only values that are valid for the department numbers in the company. Two important steps in planning tables are to identify valid values for a column and to decide how to enforce the integrity of the data in the column. Data integrity falls into these categories:
1) Entity integrity
2) Domain integrity
3) Referential integrity
4) User-defined integrity

Entity Integrity: Entity integrity defines a row as a unique entity for a particular table. Entity integrity enforces the integrity of the identifier column(s) or the primary key of a table (through indexes, UNIQUE constraints, PRIMARY KEY constraints, or IDENTITY properties).
Domain Integrity: Domain integrity is the validity of entries for a given column. You can enforce domain integrity by restricting the type (through data types), the format (through CHECK constraints and rules), or the range of possible values (through FOREIGN KEY constraints, CHECK constraints, DEFAULT efinitions, NOT NULL definitions, and rules).
Referential Integrity: Referential integrity preserves the defined relationships between tables when records are entered or deleted. In Microsoft® SQL Server™ 2000, referential integrity is based on relationships between foreign keys and primary keys or between foreign keys and unique keys (through FOREIGN KEY and CHECK constraints). Referential integrity ensures that key values are consistent across tables. Such consistency requires that there be no references to nonexistent values and that if a key value changes, all references to it change consistently throughout the database. When you enforce referential integrity, SQL Server prevents users from:
· Adding records to a related table if there is no associated record in the primary table.
· Changing values in a primary table that result in orphaned records in a related table.
· Deleting records from a primary table if there are matching related records.
For example, with the sales and titles tables in the pubs database, referential integrity is based on the relationship between the foreign key (title_id) in the sales table and the primary key (title_id) in the titles table.
User-Defined: Integrity User-defined integrity allows you to define specific business rules that do not fall into one of the other integrity categories. All of the integrity categories support user-defined integrity (all column- and table-level constraints in CREATE TABLE, stored procedures, and triggers).

Question: SQL Server runs on which TCP/IP port and From where can you change the default port?
Answer: SQL Server runs on port 1433 but we can also change it for better security and From the network Utility TCP/IP properties –>Port number.both on client and the server.

Question: What is the use of DBCC commands?
Answer:
DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.DBCC CHECKDB – Ensures that tables in the db and the indexes are correctly linked.and DBCC CHECKALLOC To check that all pages in a db are correctly allocated. DBCC SQLPERF – It gives report on current usage of transaction log in percentage. DBCC CHECKFILEGROUP – Checks all tables file group for any damage.

Question: What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Answer:
Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

Question: When do you use SQL Profiler?
Answer:
SQL Profiler utility allows us to basically track Connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc.

Question: Can you explain the role of each service?
Answer:
SQL SERVER – is for running the databases SQL AGENT – is for automation such as Jobs, DB Maintenance, Backups DTC – Is for linking and connecting to other SQL Servers.

Question: What is Normalization ?
Answer:
The logical design of the database, including the tables and the relationships between them, is the core of an optimized relational database. A good logical database design can lay the foundation for optimal database and application performance. A poor logical database design can impair the performance of the entire system.

Normalizing a logical database design involves using formal methods to separate the data into multiple, related tables. A greater number of narrow tables (with fewer columns) is characteristic of a normalized database. A few wide tables (with more columns) is characteristic of an nonnomalized database. Reasonable normalization often improves performance. When useful indexes are available, the Microsoft® SQL Server™ 2000 query optimizer is efficient at selecting rapid, efficient joins between tables.

Some of the benefits of normalization include:
·Faster sorting and index creation.
·A larger number of clustered indexes. For more information, Narrower and more compact indexes.
·Fewer indexes per table, which improves the performance of INSERT, UPDATE, and DELETE statements.
·Fewer null values and less opportunity for inconsistency, which increase database compactness.

As normalization increases, so do the number and complexity of joins required to retrieve data. Too many complex relational joins between too many tables can hinder performance. Reasonable normalization often includes few regularly executed queries that use joins involving more than four tables.

Sometimes the logical database design is already fixed and total redesign is not feasible. Even then, however, it might be possible to normalize a large table selectively into several smaller tables. If the database is accessed through stored procedures, this schema change could take place without affecting applications. If not, it might be possible to create a view that hides the schema change from the applications.

Question: Can you explain what View is in SQL ?
Answer:
View is just a virtual table nothing else which is based or we can say devlop with SQL SELECT query. So we can say that its a real database table (it has columns and rows just like a regular table),but one difference is that real tables store data,but views can’t. View data is generated dynamically when the view is referenced.And view can also references one or more existing database tables or other views. We can say that it is filter of database.

Question: How to get which Process is Blocked in SQL SERVER ?

Answer:- There are two ways to get this  sp_who and sp_who2 . You cannot get any detail about the sp_who2 but its provide more information then the sp_who . And other option from which we can find which process is blocked by other process is by using Enterprise Manager or Management Studio, these two commands work much faster and more efficiently than these GUI-based front-ends.

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SQL Server Interview Questions for DBA/Developer

• What is a DDL, DML, DCL, TCL and DSPL concept in RDBMS world?
The Data Definition Language (DDL) includes,

CREATE TABLE – creates new database table
ALTER TABLE – alters or changes the database table
DROP TABLE – deletes the database table
CREATE INDEX – creates an index or used as a search key
DROP INDEX – deletes an index

The Data Manipulation Language (DML) includes,

SELECT – extracts data from the database
UPDATE – updates data in the database
DELETE – deletes data from the database
INSERT INTO – inserts new data into the database

The Data Control Language (DCL) includes,

GRANT – gives access privileges to users for database
REVOKE – withdraws access privileges to users for database

The Transaction Control (TCL) includes,

COMMIT – saves the work done
ROLLBACK – restore the database to original since the last COMMIT

DSPL – Database Stored Procedure Language came to relational databases relatively late in the game – and thus the languages used for triggers, event handlers, and stored procedures are completely different among the database vendors. Oracle’s PL/SQL is quite different even in statement syntax from SQL Server’s Transact SQL which in turn differs again from DB2’s Stored Procedure language. And of course given the underlying differences in DDL, DML, and DCL it is inevitable that the stored procedure languages would vary in content as well as syntax.

Define candidate key, alternate key, composite key.
A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys.

A key formed by combining at least two or more columns is called composite key.

How to Reset the Identity Values?

You can set the identity values using 1. DBCC CHECKIND(TABLENAME,RESEED,0) 2. Truncate table.

What are “GRANT”, “REVOKE’ and “DENY’ statements?

GRANT
Creates an entry in the security system that allows a user in the current database to work with data in the current database or execute specific Transact-SQL statements.
Syntax
Statement permissions:

GRANT { ALL | statement [ ,…n ] }
TO security_account [ ,…n ]

Object permissions:

GRANT
{ ALL [ PRIVILEGES ] | permission [ ,…n ] }
{
[ ( column [ ,…n ] ) ] ON { table | view }
| ON { table | view } [ ( column [ ,…n ] ) ]
| ON { stored_procedure | extended_procedure }
| ON { user_defined_function }
}
TO security_account [ ,…n ]
[ WITH GRANT OPTION ]
[ AS { group | role } ]

REVOKE
Removes a previously granted or denied permission from a user in the current database.

Syntax
Statement permissions:

REVOKE { ALL | statement [ ,…n ] }
FROM security_account [ ,…n ]

Object permissions:

REVOKE [ GRANT OPTION FOR ]
{ ALL [ PRIVILEGES ] | permission [ ,…n ] }
{
[ ( column [ ,…n ] ) ] ON { table | view }
| ON { table | view } [ ( column [ ,…n ] ) ]
| ON { stored_procedure | extended_procedure }
| ON { user_defined_function }
}
{ TO | FROM }
security_account [ ,…n ]
[ CASCADE ]
[ AS { group | role } ]

DENY
Creates an entry in the security system that denies a permission from a security account in the current database and prevents the security account from inheriting the permission through its group or role memberships.

Syntax
Statement permissions:

DENY { ALL | statement [ ,…n ] }
TO security_account [ ,…n ]

Object permissions:

DENY
{ ALL [ PRIVILEGES ] | permission [ ,…n ] }
{
[ ( column [ ,…n ] ) ] ON { table | view }
| ON { table | view } [ ( column [ ,…n ] ) ]
| ON { stored_procedure | extended_procedure }
| ON { user_defined_function }
}
TO security_account [ ,…n ]
[ CASCADE ]

• What is Stored Procedure?
A stored procedure is a collection of T-SQL statements. The stored procedure stored in the system tables of the User Database in SQL Server. The system tables used in stored procedure is sysObjects, sysDepends and sysComments.

Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data and stored procedure also returns the output parameter. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_help,sp_helpdb (Alt + F1), sp_renamedb, sp_depends etc.

Stored Procedure can takes 1024 input and returns the 1024 output parameters.

• What is Trigger?
Trigger are used to enforce the business rules in the RDBMS. A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the RDBMS. Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed. The RDBMS automatically fires the trigger as a result of a data modification to the associated table.
Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.

There are two types of trigger in SQL Server 1. After Trigger 2. Instead of Trigger

Nested Trigger: Like the stored procedure trigger can also be nested upto 32 levels. A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger. For the nested trigger user has to define the execution order of the trigger.

The trigger will create two magic tables inserted and deleted which contains the structure of table on which it excutes.

• What is View?
A view is one type of virtual tables which only stores the SELECT query without data. User can perform the Insert/Update/Delete operation on the view. View can give us the better security.

User can define the index on views. The Instead of trigger can fire on the view.

• What is Index?
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 craete 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.
• What is the difference between clustered and a non-clustered index?

There are clustered and nonclustered indexes. A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows. SQL Server can create 249 Non-clustered index per table.

• What is cursors?
Cursors allow row-by-row prcessing of the resultsets. The system table used in the cursor operation is sysCursors. The cursor can be local or global.

Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information.

Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network round trip, where as a normal SELECT query makes only one round trip, however large the result set is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Further, there are restrictions on the SELECT statements that can be used with some types of cursors.

What is the use of DBCC commands?
DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB – Ensures that tables in the db and the indexes are correctly linked.
DBCC CHECKALLOC – To check that all pages in a db are correctly allocated.
DBCC CHECKFILEGROUP – Checks all tables file group for any damage.

• What is a Linked Server?
Think of a Linked Server as an alias on your local SQL server that points to an external data source. This external data source can be Access, Oracle, Excel or almost any other data system that can be accessed by OLE or ODBC–including other MS SQL servers. An MS SQL linked server is similar to the MS Access feature of creating a “Link Table.”

Stored Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.

• What’s the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.

• What is a NOLOCK?
Using the NOLOCK query optimizer hint is generally considered good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. The result is dirty read/uncommited data read. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete.

• What is difference between DELETE & TRUNCATE commands?
Delete: Delete is logged operation. Trigger can fire on the delete operation. Delete can use the where clause. Can be used in foreign key relationship tables and remove the data from the child table if the ON DELETE CASCADE is specified.
DELETE Can be Rolled back.
DELETE is DML Command.
DELETE does not reset identity of the table.

TRUNCATE
TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
TRUNCATE 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 removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. Truncate resets the identity value.

We cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
TRUNCATE can be Rolled back if it is used between Begin/Commit/Rollback transactions.
TRUNCATE is DDL Command.
TRUNCATE Resets identity of the table.

Difference between Function and Stored Procedure?
UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section whereas Stored procedures cannot be.
UDFs can return the table variable.

Inline UDF’s can be though of as views that take parameters and can be used in JOINs and other Rowset operations.

We can not write the configuration statements in UDFs. UDs can return only one value whereas SPs can return 1024 output parameters.

When is the use of UPDATE_STATISTICS command?
This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

• What types of Joins are possible with Sql Server?
Joins are used in queries to explain how different tables are related. Joins also let us select data from a table depending upon data from another table.
Types of joins: SELF JOINs, MERGE JOINs, INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.

• What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. It is the good practice to use WHERE clause with the Group By for the better performance result.

• What is SQL Profiler?

It is a tool which help us to profiling the activities at the database level. It is the good practice to use the profiler from the different machine rather than the production machine.

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. We can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performance by executing too slowly.
Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data iscollected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.

• What is User Defined Functions?
User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.

• Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties –> Port number.both on client and the server.

• What are the authentication modes in SQL Server? How can it be changed?
Windows mode and mixed mode (SQL & Windows).
• Where are SQL server users names and passwords are stored in sql server?
They get stored in master db in the sysxlogins table.

Which command using Query Analyzer will give you the version of SQL server and operating system?
SELECT SERVERPROPERTY(‘productversion’), SERVERPROPERTY (‘productlevel’), SERVERPROPERTY(‘edition’), SELECT @@version

• What is SQL server agent?

It is one of the services provided by SQL Server. Used for the scheduling purpose. To start the this service from the dos prompt you can write net start sqlserveragent
• What is @@ERROR?
The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement, it must be saved to a variable if it is needed to process it further after checking it.

• What is Raiseerror?
Stored procedures report errors to client applications via the RAISERROR command. RAISERROR doesn’t change the flow of a procedure; it merely displays an error message, sets the @@ERROR automatic variable, and optionally writes the message to the SQL Server error log and the NT application event log.

• What is log shipping?
Log shipping is the process of automating the backup of database and transaction log files on a
production SQL server, and then restoring them onto a standby server. Enterprise Editions only
supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db can be used this as the Disaster Recovery plan. The key feature of log shipping is that is will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.

• What is the difference between a local and a global variable?
User can create local temporary table using Single(#) and global temporary table using (##)A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement.
A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection are closed, the data in the global temporary table disappears. However, the table definition remains with the database for access when database is opened next time.
What command do we use to rename a db?
sp_renamedb ‘oldname’ , ‘newname’
If someone is using db it will not accept sp_renmaedb. In that case first bring db to single user using sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to bring database to multi user mode.

• What are the different types of replication? Explain.
The SQL Server 2000-supported replication types are as follows:
· Transactional
· Snapshot
· Merge
Snapshot replication distributes data exactly as it appears at a specific moment in time and does not monitor for updates to the data. Snapshot replication is best used as a method for replicating data that changes infrequently or where the most up-to-date values (low latency) are not a requirement. When synchronization occurs, the entire snapshot is generated and sent to Subscribers.

Transactional replication, an initial snapshot of data is applied at Subscribers, and then when data modifications are made at the Publisher, the individual transactions are captured and applied to Subscribers.

Merge replication is the process of distributing data from Publisher to Subscribers, allowing the
Publisher and Subscribers to make updates while connected or disconnected, and then merging the updates between sites when they are connected.
What are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)

• What does it mean to have quoted_identifier on? What are the implications of having it off?
When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.

• What is the STUFF function and how does it differ from the REPLACE function?
STUFF function to overwrite existing characters. Using this syntax, STUFF(string_expression, start,length, replacement_characters), string_expression is the string that will have characters substituted,start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string.
REPLACE function to replace existing characters of all occurance. Using this syntax
REPLACE(string_expression, search_string, replacement_string), where every incidence of
search_string found in the string_expression will be replaced with replacement_string.

• Using query analyzer, name 3 ways to get an accurate count of the number of records in a table?
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

What is the basic functions for master, msdb, model, tempdb databases?
The Master database stores the information about the sql server configuration, databases, users etc.

The msdb database stores information regarding database backups, SQL Agent information, DTS packages, backup and restore history, SQL Server jobs, and some replication information such as for log shipping.
The tempdb holds temporary objects such as global and local temporary tables and stored procedures.
The model is essentially a template database used in the creation of any new user database created in the instance.

• What are primary keys and foreign keys?
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.
Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.

• What is data integrity? Explain constraints?
Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.
A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.
A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered.The unique key constraints are used to enforce entity integrity as the primary key constraints.

A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.

A NOT NULL constraint enforces that the column will not accept null values. The not null constraints
are used to enforce domain integrity, as the check constraints.

• What is Identity?
Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set.

• What is BCP? When does it used?
BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination.

How do you load large data to the SQL server database?
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.

• How to know which index a table is using?
SELECT table_name,index_name FROM user_constraints

• How to copy the tables, schema and views from one SQL server to another?
Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and
programmable objects that lets user extract, transform, and consolidate data from disparate sources into single or multiple destinations.

• What is Self Join?
This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company have a hierarchal reporting structure whereby one member of staff reports to another.

• What is Cross Join?
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.

• Which virtual table/Magic Tables does a trigger use?
Inserted and Deleted.

• List few advantages of Stored Procedure.
· Stored procedure can reduced network traffic and latency, boosting application performance.
· Stored procedure execution plans can be reused, staying cached in SQL Server’s memory,
reducing server overhead.
· Stored procedures help promote code reuse.
· Stored procedures can encapsulate logic. You can change stored procedure code without
affecting clients.
· Stored procedures provide better security to your data.

What is an execution plan? When would you use it? How would you view the execution plan?
An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called “Show Execution Plan” (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.