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Showing posts with label Examples. Show all posts
Showing posts with label Examples. Show all posts

Friday, May 8, 2009

How to Export data from SQL Server to Excel

Problem
Exporting data from SQL Server to Excel seems like a reasonably simple request. I just need to write out a few reports for users on a regular basis, nothing too fancy, the same basic report with a few different parameters. What native SQL Server options are available to do so? Do I need to learn another tool or can I use some T-SQL commands? Does SQL Server 2005 offer any new options to enhance this process?


Solution
Exporting data from SQL Server to Excel can be achieved in a variety of ways. Some of these options include Data Transformation Services (DTS), SQL Server Integration Services (SSIS) and Bulk Copy (BCP). Data Transformation Services (SQL Server 2000) and SQL Server Integration Services (SQL Server 2005) offers a GUI where widgets can be dragged and dropped Each option has advantages and disadvantages, but all can do the job. It is just a matter of your comfort level with the tools and the best solution to meet the need.

Another option that is available directly via the T-SQL language is the OPENROWSET command (SQL Server 2000 and SQL Server 2005). This command can be called directly in any stored procedure, script or SQL Server Job from T-SQL. Below outlines the full syntax available:

Source - SQL Server 2005 Books Online

Below is a simple example of writing out the Job name and date to Sheet1 of an Excel spreadsheet in either SQL Server 2005 or 2000:

INSERT INTO OPENROWSET('Microsoft.Jet.OLEDB.4.0',
'Excel 8.0;Database=C:\testing.xls;',
'SELECT Name, Date FROM [Sheet1$]')
SELECT [Name], GETDATE() FROM msdb.dbo.
sysjobs
GO

Using the OPENROWSET command creates two caveats. The first caveat is the need to have an Excel spreadsheet serve as a template in the needed directory with the correct worksheets and columns. Without this the you would receive an error message. The second caveat is that it is necessary to enable the OPENROWSET command with the SQL Server 2005 Surface Area Configuration utility. Note - This step is not needed for SQL Server 2000. With the loop example you could copy and paste the Excel spreadsheet and load the data as needed.

Although the example above is very simple, you could integrate this simple example into your code. For example, if you had the need to write out a number of reports in the same format, you could loop (WHILE loop or Cursor) over the records and write them out to different Excel spreadsheets based on the name or report type. In addition, you could integrate this code with either SQL Server 2000 mail or Database mail (SQL Server 2005) and mail the results to the users with very little effort and build the process entirely with T-SQL.


Tuesday, April 7, 2009

SQL Server Cursor Examples

Here's some Examples on SQL Server Cursor


Problem
In my T-SQL code I always use set based operations. I have been told these types of operations are what SQL Server is designed to process and it should be quicker than serial processing. I know cursors exist but I am not sure how to use them. Can you provide some cursor examples? Can you give any guidance on when to use cursors? I assume Microsoft created them for a reason so they must have a place where they can be used in an efficient manner.

Solution
In some circles cursors are never used, in others they are a last resort and in other groups they are used regularly. In each of these camps they have different reasons for their stand on cursor usage. Regardless of your stand on cursors they probably have a place in particular circumstances and not in others. So it boils down to your understanding of the coding technique then your understanding of the problem at hand to make a decision on whether or not cursor based processing is appropriate or not. To get started let's do the following:

  • Look at an example cursor
  • Break down the components of the cursor
  • Provide additional cursor examples
  • Analyze the pros and cons of cursor usage

Example Cursor

Here is an example cursor from tip Simple script to backup all SQL Server databases where backups are issued in a serial manner:

DECLARE @name VARCHAR(50) -- database name
DECLARE @path VARCHAR(256) -- path for backup files
DECLARE @fileName VARCHAR(256) -- filename for backup
DECLARE @fileDate VARCHAR(20) -- used for file name

SET @path = 'C:\Backup\'

SELECT @fileDate = CONVERT(VARCHAR(20),GETDATE(),112)

DECLARE db_cursor CURSOR FOR
SELECT
name
FROM master.dbo.sysdatabases
WHERE name NOT IN ('master','model','msdb','tempdb')

OPEN db_cursor
FETCH NEXT FROM db_cursor INTO @name

WHILE @@FETCH_STATUS = 0
BEGIN
SET
@fileName = @path + @name + '_' + @fileDate + '.BAK'
BACKUP DATABASE @name TO DISK = @fileName

FETCH NEXT FROM db_cursor INTO @name
END

CLOSE
db_cursor
DEALLOCATE
db_cursor

Cursor Components

Based on the example above, cursors include these components:

  • DECLARE statements - Declare variables used in the code block
  • SET\SELECT statements - Initialize the variables to a specific value
  • DECLARE CURSOR statement - Populate the cursor with values that will be evaluated
    • NOTE - There are an equal number of variables in the DECLARE CURSOR FOR statement as there are in the SELECT statement. This could be 1 or many variables and associated columns.
  • OPEN statement - Open the cursor to begin data processing
  • FETCH NEXT statements - Assign the specific values from the cursor to the variables
    • NOTE - This logic is used for the initial population before the WHILE statement and then again during each loop in the process as a portion of the WHILE statement
  • WHILE statement - Condition to begin and continue data processing
  • BEGIN...END statement - Start and end of the code block
    • NOTE - Based on the data processing multiple BEGIN...END statements can be used
  • Data processing - In this example, this logic is to backup a database to a specific path and file name, but this could be just about any DML or administrative logic
  • CLOSE statement - Releases the current data and associated locks, but permits the cursor to be re-opened
  • DEALLOCATE statement - Destroys the cursor

Additional Cursor Examples

In the example above backups are issued via a cursor, check out these other tips that leverage cursor based logic:

Cursor Analysis

The analysis below is intended to serve as insight into various scenarios where cursor based logic may or may not be beneficial:

  • Online Transaction Processing (OLTP) - In most OLTP environments, SET based logic makes the most sense for short transactions. Our team has run into a third party application that uses cursors for all of its processing, which has caused issues, but this has been a rare occurrence. Typically, SET based logic is more than feasible and cursors are rarely needed.
  • Reporting - Based on the design of the reports and the underlying design, cursors are typically not needed. However, our team has run into reporting requirements where referential integrity does not exist on the underlying database and it is necessary to use a cursor to correctly calculate the reporting values. We have had the same experience when needing to aggregate data for downstream processes, a cursor based approach was quick to develop and performed in an acceptable manner to meet the need.
  • Serialized processing - If you have a need to complete a process in serialized manner, cursors are a viable option.
  • Administrative tasks - Many administrative tasks need to be executed in a serial manner, which fits nicely into cursor based logic, but other system based objects exist to fulfill the need. In some of those circumstances, cursors are used to complete the process.
  • Large data sets - With large data sets you could run into any one or more of the following:
    • Cursor based logic may not scale to meet the processing needs.
    • With large set based operations on servers with a minimal amount of memory, the data may be paged or monopolize the SQL Server which is time consuming can cause contention and memory issues. As such, a cursor based approach may meet the need.
    • Some tools inherently cache the data to a file under the covers, so processing the data in memory may or may not actually be the case.
    • If the data can be processed in a staging SQL Server database the impacts to the production environment are only when the final data is processed. All of the resources on the staging server can be used for the ETL processes then the final data can be imported.
    • SSIS supports batching sets of data which may resolve the overall need to break-up a large data set into more manageable sizes and perform better than a row by row approach with a cursor.
    • Depending on how the cursor or SSIS logic is coded, it may be possible to restart at the point of failure based on a checkpoint or marking each row with the cursor. However, with a set based approach that may not be the case until an entire set of data is completed. As such, troubleshooting the row with the problem may be more difficult.

Cursor Alternatives

Below outlines alternatives to cursor based logic which could meet the same needs: