FAQ : What is Partition Scheme in SQL Server?

Once you have created the Partition Function then the next step is to create Partition Scheme. As already mentioned, One partition function may have one or more Partition Scheme. . The partition scheme defines how any resulting partitions will be stored on filegroups. You list the filegroups for a partition scheme in the same order that you want to have them map to the partitions defined by the partition function. Creating a partition scheme assumes that you have already created the filegroups. You can mention ALL TO keyword to create all the partition to a single filegroup.

Eg. From BOL
CREATE PARTITION FUNCTION myRangePF1 (int)
AS RANGE LEFT FOR VALUES (1, 100, 1000);
GO
CREATE PARTITION SCHEME myRangePS1
AS PARTITION myRangePF1
TO (test1fg, test2fg, test3fg, test4fg);

Edit : Should Filegroup single file or multiple files considered as out of scope in this context. But selecting single filegroup VS multiple filegroup and Single files per filegroup VS multiple files also a significant decision to be made in terms of performance.

FAQ : What is Partition Function in SQL Server?

Partition functions are special kind of objects (of course created by user) created in a database which can be used only by partition scheme. Partition function contains a data type , that must be the same data type as the partition column chosen in the table. Partition Function as such not directly related to any table.

NOTE: Even though Partition Function to Partition scheme is One to Many, in sliding window scenario moving data between in and out of partition is a common requirement, which require Partition function modification. So practically it makes each Partition table should have exclusive partition function and scheme.
Partition functions are not user defined functions.

Here are few of facts to be known about partition functions• Partition functions are not listed as database objects in the sys.all_objects or sys.objects system tables; instead, you can find them listed in sys.partition_functions.
• Partition functions are not contained by a database schema.
• Special commands must be used for creating, altering, and dropping a partition function:
o CREATE PARTITION FUNCTION
o ALTER PARTITION FUNCTION
o DROP PARTITION FUNCTION
• Partition functions can be invoked interactively in Transact-SQL by using the $PARTITION function.

Partition Functions System Objects

• sys.partition_functions : Contains a row for each partition function.
• sys.partition_range_values : Contains a row for each range boundary value of a partition function of type R.
• sys.partition_parameters : Contains a row for each parameter of a partition function.
• $PARTITION. :Returns the partition number into which a set of partitioning column values would be mapped for any specified partition function.
Eg. SELECT $PARTITION.RangePF1 (10) ;

FAQ : What is the advantages and disadvantages of Table Partitioning of 2005 over Partition View of earlier versions?

Advantage of Table Partitioning
• No need to create separate physical tables for each ranges manually.
• There are few limitations when you insert data into Partition View like you cannot use BULK INSERT/BCP etc.
• Less complex to manage and administrate
• SQL Server automatically manages the placement of data in the proper partitions.


Disadvantage of Table Partitioning
• Major disadvantage is, we cannot have different index model for different range. Ie. In general, we may need to have more number of indexes when the data is READ ONLY and less or different index model for the data which is READWRITE. That is not possible with partition table.
• You cannot rebuild a partitioned index with the ONLINE option set to ON, because the entire table will be locked during the rebuild.

Partition is not recommended for a table in following condition

1. If you want to have different indexing structure for READ ONLY and READ WRITE data then partition is not recommended.
2. If the table is not accessed much or do not required much index maintenance
3. If the query on the tables are filtered(WHERE condition) by some column which cannot be used for partitioned.
4. If you planning to use ONLINE INDEX REBUILD option you cannot use partition. You cannot rebuild a partitioned index with the ONLINE option set to ON, because the entire table will be locked during the rebuild.

FAQ: How to determine partition suits for a table ?

There are few general guidelines for determining whether the partition feature is suited for a table or not. One point to be noted here is, if a table is not partitioned properly (ie. Not selected the most suitable partition column), though it will not adversely affect the performance but it will not give any performance benefit either. Remember that the query optimizer can limit the partitions that are scanned to resolve a query only if the query filters on the partitioning column. Precisely, just because the table is partitioned, we will not have performance benefit.

1. First of all, just because of a table is big, it should not be partitioned. Ie. Only size of the table cannot be "THE" criteria for partition.
2. If the index maintenance on a table is time consuming or make the table offline for the users, you may opt partition because re-indexing on only required partition is better than re-indexing the whole table. Partitioning a large table divides the table and its indexes into smaller partitions, so that maintenance operations can be applied on a partition-by-partition basis, rather than on the entire table.
3. You can go for partition if the data must be aged out of the table (archived) periodically and the current delete process is taking time or blocking other users.
4. If the table is loaded with new data periodically and the loading process takes time and the table data lends itself to a partition column based on ascending date or time we may go for partition.
5. Table backup of huge table can be managed smartly by using new backup features of sql server 2005 and partitioning.
6. To summarize, the best way to put this in single statement is, if you have any table which fits into SLIDING WINDOW scenario you must partition it.

FAQ: What all are the types of table partitions in SQL Server

There are two types of partitions. Horizontal and vertical.

Horizontal partition
Horizontal partition divides the data on subset of rows. Ie. Divide the data in such a way that all the rows of single year /month /week(Range) may be in one partition kind. In earlier versions of SQL Server this method was achieved by creating physical tables for each subsets and UNION the tables using a View(Partition View) and application access the data using Views.

Vertical partition
In Vertical Partition , the columns of a very wide table are spread across multiple physical tables containing distinct subsets of the columns with the same number of rows. The relation would be ONE TO ONE among the tables. The result is multiple tables containing the same number of rows but different columns, usually with the same primary key column in each table. Often a view is defined across the multiple tables and queries directed against the view.

FAQ : What is Table Partitioning in SQL Server?

Partitioning is the process of dividing data into small , more manageable chunks. We can divide the data horizontally (on rows ) or vertically (on columns) . Table partitioning can make very large tables and indexes easier to manage, and improve the performance of APPROPRIATELY FILTERED queries. Horizontal Partitioning is one of the new feature added in SQL Server 2005 (in earlier versions we used to create separate physical table and create a wrapper view which union all the tables which is also known as Partition View). When a table is created as a partitioned table, SQL Server automatically places the table's rows in the correct partition, and SQL Server maintains the partitions behind the scenes. You can then perform maintenance operations on individual partitions, and properly filtered queries will access only the correct partitions. But it is still one table as far as SQL Server is concerned

FAQ : How to disable AUTO UPATE STATISTICS for a specific table or index in SQL Server

Using sp_autostats system stored procedure we can switch off AUTO UPDATE STATISTICS on a specific table or index. Please note that, if AUTO UPDATE STAT is OFF in Database level, you can not switch ON object level. In otherwords, if the DB level Auto update stat is ON then you can override the DB level setting and switch off AUTO UPDATE STAT object level using this stored procedure.

Syntax
sp_autostats [ @tblname = ] 'table_name'
[ , [ @flagc = ] 'stats_flag' ]
[ , [ @indname = ] 'index_name' ]


Enabling automatic statistics for all indexes of a table
The following example enables the automatic statistics setting for all indexes of the Product table.

USE AdventureWorks;
GO
EXEC sp_autostats 'Production.Product', 'ON'

FAQ : Why we need to have different service account for each service in SQL Server?

In SQL Server, as per the components we select, different services gets installed like SQL SERVER Database engine, Analysis Service, Integration Services, Reporting Services and SQL Server Agent Services. But each service have its own specific tasks to do which requires different privilege and permissions. If we are configuring all the services startup account with a single user, this user will have to have a sum of all the permission required by all the services, which is very against security policy recommended by Microsoft. For eg. DB Engine needs permission to the folder where the data and log files are kept why because it has to write the data into these files. Whereas SQL Server Agent does not need this permission. So, if we are using same user for both the services, if the SQL Server Agent service got hacked or compromised , even the database engine is at risk. This is the very basic reason why we need different windows user for each service.

FAQ : What is Domain of a column? How it defer from Datatype

Domain of a columm is the set of the values that are applicable for a column. For example, Gender column can have Female or Male so these value make the domain for Gender column.

Though Domain and Datatype looks similar but it is not so. Datatype is the type of data that can be stored in the column . ie. Integer datatype column can only store numeric data.

FAQ : What is the difference between Framework and Standard?

We have heard lot about ITIL and ISOS. Here ITIL is framework where as ISOS is Standard. What is the difference between standard and framework? Have you ever thought about this?

Standard : Standard is something very rigid which should be followed across. Standard will define proper method to do a process. ISOS is a standard.

Framework : Framework is something where you have the boundary defined. It is flexible and not always defined with step by step process. ITIL is a framework.

FAQ : What is SQL Server PRINT equivalent in Oracle

Print In SQL Server
Returns a user-defined message to the client. Mainly Print is used while debugging procedures or triggers.
Eg
PRINT N'This is from first Loop.';

Oracle Equivalent :
What can come close in Oracle is DBMS_OUTPUT.PUT_LINE. Dbms_output is a PL/SQL Package which has a put_line procedure which write data to flat file or to direct your PL/SQL output to a screen.

DBMS_OUTPUT.PUT_LINE ('This is from first Loop);

FAQ : What is Oracle Predefined Exceptions equivalent in SQL Server

What is Oracle Predefined Exceptions
An exception is a runtime error or warning condition, which can be predefined or user-defined. Predefined exceptions are raised implicitly (automatically) by the runtime system. User-defined exceptions must be raised explicitly by RAISE statements. To handle raised exceptions, you write separate routines called exception handlers. PL/SQL declares predefined exceptions globally in package STANDARD, which defines the PL/SQL environment. So, you need not declare them yourself.
Here are few examples
NO_DATA_FOUND : A SELECT INTO statement returns no rows, or your program references a deleted element in a nested table or an uninitialized element in an index-by table. SQL aggregate functions such as AVG and SUM always return a value or a null. So, a SELECT INTO statement that calls an aggregate function never raises NO_DATA_FOUND. The FETCH statement is expected to return no rows eventually, so when that happens, no exception is raised.

TOO_MANY_ROWS : A SELECT INTO statement returns more than one row.

DUP_VAL_ON_INDEX : Your program attempts to store duplicate values in a database column that is constrained by a unique index.

Read more about Predefined exceptions here

What is SQL Server Equivalent?

Till SQL Server 2008 we do not have any equivalent. Ie there is no Predefined Exceptions in SQL Server. But this can be achieved by BEGIN TRY .. END TRY BEGIN CATCH … END CATCH. ERROR Number/Message combination.

FAQ : Oracle %ROWTYPE equivalent in SQL Server

What is %ROWTYPE in Oracle?

The %ROWTYPE attribute provides a feature to create Table based or Cursor Based record. Ie. If you have a table with 5 column and you want to select all the five column value of a single record at a stretch instead of declaring 5 scalar variable you just declare a single variable of %ROWTYPE which will intern have all the five column. Consider we have a table called Department with three columns Department_ID, Description and Name. Either you can declare three scalar variable or you can declare single variable of %ROWTYPE attribute. If you want to store a collection (multiple records ) then you can use TABLE OF TableName%RowType;
See the below eg.
DECLARE
Dept_REC DEPARTMENT%ROWTYPE;
BEGIN
SELECT *
INTO Dept_REC
FROM DEPARTMENT
WHERE DEPARTMENT_ID = 1;
DBMS_OUTPUT.PUT_LINE (' DEPARTMENT ID: '|| Dept_REC.DEPARTMENT_ID);
DBMS_OUTPUT.PUT_LINE ('COURSE DESCRIPTION: '||
Dept_REC.DESCRIPTION);
DBMS_OUTPUT.PUT_LINE ('Name: '||
Dept_REC.Name);
END;

SQL Server Equivalent.

In SQL Server what can come close to TABLE OF TableName%RowType is Declare a table type variable (in case it is collection). Another way may be create a #temp table. But temp table method may involve IO which need to be aware of and also in there are limitation where you can create #temp table. For a single row, it is better to declare separate scalar variable for each columns

Table variable Method
Declare @Dept Table (Department_id Int,Name Varchar(100),Description Varchar(1000))
The below statement will insert all the rows from Department to @Dept variable.
Select *INTO @Dept
FROM
Department

Temp table method
Select *into #Temp_Dept
FROM Department
The above statement will create a temp table on the fly. This can be used in Procedure but not in Function.

FAQ : What is SQL Server Profiler equivalent in Oracle

What is SQL Server Profiler?

Microsoft SQL Server Profiler is a graphical user interface to SQL Trace for monitoring an instance of the Database Engine or Analysis Services. You can capture and save data about each event to a file or table to analyze later. For example, you can monitor a production environment to see which stored procedures are affecting performance by executing too slowly. Basically this tool is a wrapper which internally calls SQL Trace system stored procedures. Generally, running profiler is not recommended in production if you need to trace events, then in production it is better to go for SQL Trace system Stored procedure. Refer this link for more info.

Oracle Equivalent . (please note that this is based on my little experience in Oracle and If anyone feels that If I am going wrong please feel free to correct me)

Automatic Workload Repository (AWR)

Oracle offers many ways to trace events which again later version may have new tools and features. In 10 G, Oracle offers Automatic Workload Repository (AWR) which is used to collect statistics including
• Wait events used to identify performance problems.
• Time model statistics indicating the amount of DB time associated with a process from the V$SESS_TIME_MODEL and V$SYS_TIME_MODEL views.
• Active Session History (ASH) statistics from the V$ACTIVE_SESSION_HISTORY view.
• Some system and session statistics from the V$SYSSTAT and V$SESSTAT views.
• Object usage statistics.
• Resource intensive SQL statements.

Read more about AWR here

SQL trace files and TKPROF

If you are still in Oracle 9, you can go for SQL trace files which gives you statement by statement log of SQL and PL/SQL executed by Database Client(s). The SQL Trace facility and TKPROF are two basic performance diagnostic tools that can help you monitor and tune applications running against the Oracle Server. SQL Trace files entries can be classified in to mainly four categories.
• Database calls (parse, execute, and fetch)
• Wait events
• Bind variable values
• Miscellaneous events like timestamps, instance service name, session, module, action, and client
identifier

TKPROF

You can run the TKPROF program to format the contents of the trace file and place the output into a readable output file. Optionally, TKPROF can also:
• Determine the execution plans of SQL statements
• Create a SQL script that stores the statistics in the database
Read more about SQL Trace files and TKPROF here

FAQ: What is optimizer in SQL Server?

Unlike procedural language SQL Statements does not state the exact steps that database engine should follow to extract the data or manipulate the data. In procedural language the statements are ran as per the sequence they have written. But in SQL , database engine must analyse the statement to determine the most efficient way to extract/manipulate data. This process is called optimization and the component which does this process is called Optimizer.

The input to the optimizer contains , Query , schema (table/indexes definitions) and the statistics available.

The output from the optimizer is query execution plan.



The SQL Server query optimizer is a cost-based optimizer. Each possible execution plan has an associated cost in terms of the amount of computing resources used. The query optimizer must analyze the possible plans and choose the one with the lowest estimated cost. Some complex SELECT statements have thousands of possible execution plans. In these cases, the query optimizer does not analyze all possible combinations. Instead, it uses complex algorithms to find an execution plan that has a cost reasonably close to the minimum possible cost.

FAQ : What is Optimizing SQL statement .

Unlike procedural language SQL Statements does not state the exact steps that database engine should follow to extract the data or manipulate the data. In procedural language the statements are ran as per the sequence they have written. But in SQL , database engine must analyse the statement to determine the most efficient way to extract/manipulate data. This process is called optimization.

FAQ : What is the equivalent of SELECT * INTO of SQL Server in Oracle

SQL Server
Select * into TargettableName from sourceTableName

Oracle
Create table targetTableName as Select *From sourceTableName

FAQ : What is Packages in Oracle and its equivalent in SQL Server

A package is a schema object that groups logically related PL/SQL types, variables, and subprograms. Packages usually have two parts, a specification (spec) and a body; sometimes the body is unnecessary. The specification is the interface to the package. It declares the types, variables, constants, exceptions, cursors, and subprograms that can be referenced from outside the package. The body defines the queries for the cursors and the code for the subprograms.

There is no equivalent in SQL Server yet.

FAQ : How to declare a variable in SQL Server (T-SQL) and in Oracle PL/SQL

SQL Server

Variables are declared in the body of a batch or procedure with the DECLARE Statement and are assigned to values with either a SET or SELECT Statement.After declaration all variables are initialized as NULL
Variables are often used in batch or procedure /functions as counters for WHILE, LOOP or for an IF..ELSE block. Variables can be used only in expression, not in the place of object names or key words (in that case you need to use Dynamic SQL. See Dynamic SQL for more info).

Types of Variable : Three types of variables are available
• @local variable
• @Cursor_Variable_Name
• @table_variable_name

Declare a variable :
DECLARE @VariableName datatype : Variable prefixed with @ symbol.
Eg. DECLARE @Count INT
DECLARE @Name varchar(50), @Address varchar(200)

Seting /initialising a variable :

SET @Name=’Madhu’
SET @Count=100
Initialise multiple variable using Select statement :

SET can be used for only single variable where as SELECT can be used for multiple variable in a single statement

SELECT @Name=’Madhu’ , @Count=0 , @Address=’XYZ’

WHILE(@i<@Count)
BEGIN
SET @i=@i+1
PRINT @i
END

Oracle (PL/SQL) : Declaring Variables
In oracle, Variables can have any SQL datatype, such as CHAR, DATE, or NUMBER, or a PL/SQL-only datatype, such as BOOLEAN or PLS_INTEGER. For example, assume that you want to declare variables for part data, such as part_no to hold 6-digit numbers and in_stock to hold the Boolean value TRUE or FALSE. You declare these and related part variables as shown in Example 1. Note that there is a semi-colon (;) at the end of each line in the declaration section.

Example 1–1. Declaring Variables in PL/SQL
DECLARE
part_no NUMBER(6);
part_name VARCHAR2(20);

You can also declare nested tables, variable-size arrays (varrays for short), and records using the TABLE, VARRAY, and RECORD composite datatypes.

Assigning Values to a Variable
You can assign values to a variable in three ways. The first way uses the assignment operator (:=), a colon followed by an equal sign, as shown in Example 2. You place the variable to the left of the operator and an expression, including function calls, to the right. Note that you can assign a value to a variable when it is declared.

Example 1–2 Assigning Values to Variables With the Assignment Operator
DECLARE
wages NUMBER;
hours_worked NUMBER := 40;
emp_rec1 employees%ROWTYPE;
country := UPPER('Canada');


The second way to assign values to a variable is by selecting (or fetching) database values into it. In Example 1–3, 10% of an employee's salary is selected into the bonus variable. Now you can use the bonus variable in another computation or insert its value into a database table.

Example 1–3 Assigning Values to Variables by SELECTing INTO

DECLARE
bonus NUMBER(8,2);
emp_id NUMBER(6) := 100;
BEGIN
SELECT salary * 0.10 INTO bonus FROM employees
WHERE employee_id = emp_id;
END;

The third way to assign a value to a variable is by passing it as an OUT or IN OUT parameter to a subprogram, and then assigning the value inside the subprogram.