.Net Database Interview Questions 12

Using query analyzer, name 3 ways you can get an accurate count of the number of records in a table.
Answer1.
a. Select count(*) from table1
b. SELECT object_name(id) ,rowcnt FROM sysindexes WHERE indid IN (1,0) AND OBJECTPROPERTY(id, ‘IsUserTable’) = 1
c. exec sp_table_validation @table = ‘authors’

Answer2.
SELECT count( * ) as totalrecords FROM employee
This will display total records under the name totalrecords in the table employee

use COUNT_BIG
Returns the number of items in a group.

@@ROWCOUNT
Returns the number of rows affected by the last statement.
Use this statement after an SQL select * statement, to retrieve the total number of rows in the table

What is the purpose of using COLLATE in a query?
Answer1.
Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case-sensitivity, accent marks, kana character types and character width.

Answer2.
COLLATE is a clause that can be applied to a database definition or a column definition to define the collation, or to a character string expression to apply a collation cast.

What is one of the first things you would do to increase performance of a query? For example, a boss tells you that “a query that ran yesterday took 30 seconds, but today it takes 6 minutes”?
Answer1.
Use Storedprocedure for any optimized result, because it is an compiled code.

Answer2.
One of the best ways to increase query performance is to use indexes.

What is an execution plan? When would you use it? How would you view the execution plan?
The Query Analyzer has a feature called Show Execution Plan. This option allows you to view the execution plan used by SQL Server’s Query Optimizer to actually execute the query. This option is available from the Query menu on the main menu of Query Analyzer, and must be turned on before the query is executed. Once the query is executed, the results of the execution plan are displayed in graphical format in a separate window, available from a tab that appears below the query results window on the screen.

What is the STUFF function and how does it differ from the REPLACE function? Answer1:
stuff-> inserts into it without removing any thing. Replace->replace the given text with the new one.

Answer2:
STUFF - it deletes a specified length of characters and inserts another set of characters at a specified starting point. REPLACE -Replaces all occurrences of a specified string value with another string value.

What does it mean to have quoted_identifier on? What are the implications of having it off?
SET QUOTED_IDENTIFIER ON- Causes SQL Server to follow the SQL-92 rules regarding quotation mark delimiting identifiers and literal strings. Identifiers delimited by double quotation marks can be either Transact-SQL reserved keywords or can contain characters not usually allowed by the Transact-SQL syntax rules for identifiers.

What is the difference between a Local temporary table and a Global temporary table? How is each one used?
Answer1:
Local templrary table will have a single # (#tablename) appended with the table name.Global templrary table will have Double # (##tablename) appended with the table name.
Ex:create table #table1
local temp. table will be available until the session who created it logs out, but global temp. table is available till the last session gets close in SQLServer.

Answer1:
Local temporary tables are visible only in the current session; global temporary tables are visible to all sessions.Prefix local temporary table names with single number sign (#table_name), and prefix global temporary table names with a double number sign (##table_name).

What are cursors? Name four type of cursors and when each one would be applied?
Opening a cursor on a result set allows processing the result set one row at a time.
The four API server cursor types supported by SQL Server are:
a) Static cursors
b) Dynamic cursors
c) Forward-only cursors
d) Keyset-driven cursors

What is the purpose of UPDATE STATISTICS?
UPDATE STATISTICS- it updates information about the distribution of key values for one or more statistics groups (collections) in the specified table or indexed view.

How do you use DBCC statements to monitor various ASPects of a SQL Server installation?
Database Consistency Checker (DBCC) - Is a statement used to check the logical and physical consistency of a database, check memory usage, decrease the size of a database, check performance statistics, and so on. Database consistency checker (DBCC) ensures the physical and logical consistency of a database, but is not corrective. DBCC can help in repairing or checking the installation in case of any failure.

What is referential integrity and how can we achieve it?
Referential integrity preserves the defined relationships between tables when records are entered or deleted. In SQL Server, referential integrity is based on relationships between foreign keys and primary keys or between foreign keys and unique keys. 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.
We can achieve this by using foreign key.