SQL Server 2005 Interview Questions

• 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

 

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