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• Recursive Batch File

  - by MCZ

  I have a file that looks this: head1,head2,head3,head4,head5,head6 a11,a12,keyA,a14,a15,a16 a21,a22,keyB,a24,a25 a31,a32,keyC,a34 a41,a42,keyB,a44,a44 a51,a52,keyA,a54,a55,a56 a61,a62,keyA,a64,a65,a66 a71,a72,keyC,a74 some message Objective: Write list of unique keys to a text file. For example, the result for the file described above should be: keyA, keyB, keyC Here's the pseudocode I would like to implement in batch file recur.bat Read second line of inputfile If no key exist on second line, return else continue Append keyX to list FINDSTR /v keyX inputfile Pipe results to recur.bat I don't know if this is the most efficient way to do this without using actual programming language. Any suggestions for actual batch file code?

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• SQL Query fields change to uppercase on upload to server.

  - by Conor H

  Hi There, I have just finished developing an app using CodeIgniter. When I upload it to my Host (Hostgator shared) some of the SQL text is converted to uppercase and rendering the app unusable. In my database I have two tables client and transaction. When I upload the App to the server client and transaction is replaced with all caps. Obviously this is bad as MySQL queries are case sensitive. At first I was uploading with FTP and thought FTP was to blame. I then zipped up the app and uploaded the archive, unpacking it on the server shell. Still no joy. Any ideas on how to fix this? At the moment I just have to go into the server and edit my queries back to lowercase.. Cheers in advance for any ideas.. --Conor

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• bind: blackhole for invalid recursive queries?

  - by Udo G

  I have a name server that's publicly accessible since it is the authoritative name server for a couple of domains. Currently the server is flooded with faked type ANY requests for isc.org, ripe.net and similar (that's a known distributed DoS attack). The server runs BIND and has allow-recursion set to my LAN so that these requests are rejected. In such cases the server responds just with authority and additional sections referring the root servers. Can I configure BIND so that it completely ignores these requests, without sending a response at all?

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• Effects of internet connection speeds on server queries

  - by SephMerah

  Can my internet connection significantly effect queries run on phpmyadmin? I am currently 18 down and 30 up. I switched internet connections today and noticed a deep drop in query performance. The query that I am running is SELECT * FROM table. Simple. The table has one row of data. The MySQL server is on the same server as everything else. It is a VPS. Godaddy hosts. I dont have any other information. Centos 6.3 MySQL 5.1 PhpMyAdmin 3.4 Okay used google tools to inspect the XHR going out and coming in and this is what it reported. {"success":true,"message":"<div class=\"success\">Your SQL query has been executed successfully ( Query took 0.0033 sec )<\/div>","sql_query":"<div id=\"result_query\" align=\"\">\n<div class=\"success\">Your SQL query has been executed successfully ( Query took 0.0033 sec ) SNIP..................."}. So apparently my server is fine. The strange thing is though.. The returned XHR comes back exactly as soon as I execute the query on the page. It comes back within less than a second. Why PhpMyadmin does not report the change immediately. I am going to try a re-install.

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• Tool for downloading an entire site (recursive and Flash links processing)

  - by Ezequiel

  We need to replicate a working Flash site. The problem is that we don´t have access to the source code (the site is mainly a full Flash site). What is a tool to recursively download the site? The tool should process SWF files to extract the links in it. I´ve once used Teleport, but as far as I´m concerned it cannot process SWF.

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• Delete recursive directorys with FTP command on Bash

  - by Fake4d

  I have a problem with my infrastructure here. I am in a closed DMZ and have to access a FTP-Server in another DMZ from a headless Suse Linux 10.1. So i think i only got the ftp command.. But i have to delete a directory with about 100 subdirectorys and endless files in it.. When I type del directory it returns "Its not empty" and so i have to delete each sub directory and file manually. Oh please tell me a way how i can do this automatically :)

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• Recursive Unrar with Deletion as it progresses

  - by Jharwood

  Basically, i have a set of directories that are constantly being filled with .rar's, and i need to be able to extract them in place with automatic deletion of the left over .(rar|rXX) files. How would i go about this? Note: I can't delete all of them once done, they have to be deleted as the script completes one rar set. Example Directory Structure: / /folder1/ /file1.rar /file1.r00 /file1.r01 /folder2/ /sub.folder1/ /file2.part001.rar (contains a directory "file2") /file2.part002.rar /file2.part003.rar /sub.folder2/ /file3.rar /file3.r00 /file3.r01 Expected Result: / /folder1/ /file1.ext /folder2/ /sub.folder1/ /file2/ /file2.ext /sub.folder2/ /file3.ext

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• Recursive rm with condition in Linux

  - by zengr

  I have the following folder structure: parent - folder1 - main1.x - main1.y - main1.z - main1-626262.x - main1-626263.x - main1-626264.x - main1-626265.x - main1-626266.x - main1-626267.x - folder2 - main2.x - main2.y - main2.z - main2-726262.x - main2-726263.x - main2-726264.x - main2-726265.x - main2-726266.x - main2-726267.x Now, I want to remove: main-*********.x So, my required folder structure: parent - folder1 - main1.x - main1.y - main1.z - folder2 - main2.x - main2.y - main2.z So, how can I achieve this?

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• Recursive rm with condition in Linux

  - by zengr

  I have the following folder structure: parent - folder1 - main1.x - main1.y - main1.z - main1-626262.x - main1-626263.x - main1-626264.x - main1-626265.x - main1-626266.x - main1-626267.x - folder2 - main2.x - main2.y - main2.z - main2-726262.x - main2-726263.x - main2-726264.x - main2-726265.x - main2-726266.x - main2-726267.x Now, I want to remove: main-*********.x So, my required folder structure: parent - folder1 - main1.x - main1.y - main1.z - folder2 - main2.x - main2.y - main2.z So, how can I achieve this?

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• Seeing double-cursor in 'recursive RDP'

  - by John

  I'm using a Virtual PC VM on my PC to connect to a remote PC using RDP over a VPN. It works just fine except that in the RDP session, I often see a double mouse cursor... I get a standard mouse-arrow and the context-specific cursor such as a caret or hourglass. It's not a big problem but rather annoying and I wondered if there's any way to fix it, or at least understand where it comes from? Is it because I'm effectively running one RDP session from inside another? My host PC runs W7, my local VM runs XP, and the remote PC access using RDP is W7. Thankyou for any help.

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• return the result of a query and the total number of rows in a single function

  - by csotelo

  This is a question as might be focused on working in the best way, if there are other alternatives or is the only way: Using Codeigniter ... I have the typical 2 functions of list records and show total number of records (using the page as an alternative). The problem is that they are rather large. Sample 2 functions in my model: count Rows: function get_all_count() { $this->db->select('u.id_user'); $this->db->from('user u'); if($this->session->userdata('detail') != '1') { $this->db->join('management m', 'm.id_user = u.id_user', 'inner'); $this->db->where('id_detail', $this->session->userdata('detail')); if($this->session->userdata('management') === '1') { $this->db->or_where('detail', 1); } else { $this->db->where("id_profile IN ( SELECT e2.id_profile FROM profile e, profile e2, profile_path p, profile_path p2 WHERE e.id_profile = " . $this->session->userdata('profile') . " AND p2.id_profile = e.id_profile AND p.path LIKE(CONCAT(p2.path,'%')) AND e2.id_profile = p.id_profile )", NULL, FALSE); $this->db->where('MD5(u.id_user) <>', $this->session->userdata('id_user')); } } $this->db->where('u.id_user <>', 1); $this->db->where('flag <>', 3); $query = $this->db->get(); return $query->num_rows(); } results per page function get_all($limit, $offset, $sort = '') { $this->db->select('u.id_user, user, email, flag'); $this->db->from('user u'); if($this->session->userdata('detail') != '1') { $this->db->join('management m', 'm.id_user = u.id_user', 'inner'); $this->db->where('id_detail', $this->session->userdata('detail')); if($this->session->userdata('management') === '1') { $this->db->or_where('detail', 1); } else { $this->db->where("id_profile IN ( SELECT e2.id_profile FROM profile e, profile e2, profile_path p, profile_path p2 WHERE e.id_profile = " . $this->session->userdata('profile') . " AND p2.id_profile = e.id_profile AND p.path LIKE(CONCAT(p2.path,'%')) AND e2.id_profile = p.id_profile )", NULL, FALSE); $this->db->where('MD5(u.id_user) <>', $this->session->userdata('id_user')); } } $this->db->where('u.id_user <>', 1); $this->db->where('flag <>', 3); if($sort) $this->db->order_by($sort); $this->db->limit($limit, $offset); $query = $this->db->get(); return $query->result(); } You see, I repeat the most of the functions, the difference is that only the number of fields and management pages. I wonder if there is any alternative to get as much results as the query in a single function. I have seen many tutorials, and all create 2 functions: one to count and another to show results ... Will there be more optimal?

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• SQL SERVER – Server Side Paging in SQL Server 2011 – A Better Alternative

  - by pinaldave

  Ranking has improvement considerably from SQL Server 2000 to SQL Server 2005/2008 to SQL Server 2011. Here is the blog article where I wrote about SQL Server 2005/2008 paging method SQL SERVER – 2005 T-SQL Paging Query Technique Comparison (OVER and ROW_NUMBER()) – CTE vs. Derived Table. One can achieve this using OVER clause and ROW_NUMBER() function. Now SQL Server 2011 has come up with the new Syntax for paging. Here is how one can easily achieve it. USE AdventureWorks2008R2 GO DECLARE @RowsPerPage INT = 10, @PageNumber INT = 5 SELECT * FROM Sales.SalesOrderDetail ORDER BY SalesOrderDetailID OFFSET @PageNumber*@RowsPerPage ROWS FETCH NEXT 10 ROWS ONLY GO I consider it good enhancement in terms of T-SQL. I am sure many developers are waiting for this feature for long time. We will consider performance different in future posts. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Remove Debug Button in SSMS – SQL in Sixty Seconds #020 – Video

  - by pinaldave

  SQL in Sixty Seconds is indeed tremendous fun to do. Every week, we try to come up with some new learning which we can share in Sixty Seconds. In this busy world, we all have sixty seconds to learn something new – no matter how much busy we are. In this episode of the series, we talk about another interesting feature of SQL Server Management Studio. In SQL Server Management Studio (SSMS) we have two button side by side. 1) Execute (!) and 2) Debug (>). It is quite confusing to a few developers. The debug button which looks like a play button encourages developers to click on the same thinking it will execute the code. Also developer with a Visual Studio background often click it because of their habit. However, Debug button is not the same as Execute button. In most of the cases developers want to click on Execute to run the query but by mistake they click on Debug and it wastes their valuable time. It is very easy to fix this. If developers are not frequently using a debug feature in SQL Server they should hide it from the toolbar itself. This will reduce the chances to incorrectly click on the debug button greatly as well save lots of time for developer as invoking debug processes and turning it off takes a few extra moments. In this Sixty second video we will discuss how one can hide the debug button and avoid confusion regarding execution button. I personally use function key F5 to execute the T-SQL code so I do not face this problem that often. More on Removing Debug Button in SSMS: SQL SERVER – Read Only Files and SQL Server Management Studio (SSMS) SQL SERVER – Standard Reports from SQL Server Management Studio – SQL in Sixty Seconds #016 – Video SQL SERVER – Discard Results After Query Execution – SSMS SQL SERVER – Tricks to Comment T-SQL in SSMS – SQL in Sixty Seconds #019 – Video SQL SERVER – Right Aligning Numerics in SQL Server Management Studio (SSMS) I encourage you to submit your ideas for SQL in Sixty Seconds. We will try to accommodate as many as we can. If we like your idea we promise to share with you educational material. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video

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• SQL SERVER – Difference Between GETDATE and SYSDATETIME

  - by pinaldave

  Sometime something so simple skips our mind. I never knew the difference between GETDATE and SYSDATETIME. I just ran simple query as following and realized the difference. SELECT GETDATE() fn_GetDate, SYSDATETIME() fn_SysDateTime In case of GETDATE the precision is till miliseconds and in case of SYSDATETIME the precision is till nanoseconds. Now the questions is to you – did you know this? Be honest and please share your views. I already accepted that I did not know this in very first line. Reference: Pinal Dave (http://www.SQLAuthority.com), Filed under: Pinal Dave, SQL, SQL Authority, SQL DateTime, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – When are Statistics Updated – What triggers Statistics to Update

  - by pinaldave

  If you are an SQL Server Consultant/Trainer involved with Performance Tuning and Query Optimization, I am sure you have faced the following questions many times. When is statistics updated? What is the interval of Statistics update? What is the algorithm behind update statistics? These are the puzzling questions and more. I searched the Internet as well many official MS documents in order to find answers. All of them have provided almost similar algorithm. However, at many places, I have seen a bit of variation in algorithm as well. I have finally compiled the list of various algorithms and decided to share what was the most common “factor” in all of them. I would like to ask for your suggestions as whether following the details, when Statistics is updated, are accurate or not. I will update this blog post with accurate information after receiving your ideas. The answer I have found here is when statistics are expired and not when they are automatically updated. I need your help here to answer when they are updated. Permanent table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in a table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Temporary table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in table is less than 6, statistics is updated for every 6 changes in table. If the number of rows in table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Table variable There is no statistics for Table Variables. If you want to read further about statistics, I suggest that you read the white paper Statistics Used by the Query Optimizer in Microsoft SQL Server 2008. Let me know your opinions about statistics, as well as if there is any update in the above algorithm. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Question, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Statistics

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• SQL SERVER – FT_IFTS_SCHEDULER_IDLE_WAIT – Full Text – Wait Type – Day 13 of 28

  - by pinaldave

  In the last few days during this series, I got many question about this Wait type. It would be great if you read my original related wait stats query in the first post because I have filtered it out in WHERE clause. However, I still get questions about this being one of the most wait types they encounter. The truth is, this is a background task processing and it really does not matter and it should be filtered out. There are many new Wait types related to Full Text Search that are introduced in SQL Server 2008. If you run the following query, you will be able to find them in the list. Currently there is not enough information for all of them available on BOL or any other place. But don’t worry; I will write an in-depth article when I learn more about them. SELECT * FROM sys.dm_os_wait_stats WHERE wait_type LIKE 'FT_%' The result set will contain following rows. FT_RESTART_CRAWL FT_METADATA_MUTEX FT_IFTSHC_MUTEX FT_IFTSISM_MUTEX FT_IFTS_RWLOCK FT_COMPROWSET_RWLOCK FT_MASTER_MERGE FT_IFTS_SCHEDULER_IDLE_WAIT We have understood so far that there is not much information available. But the problem is when you have this Wait type, what should you do?  The answer is to filter them out for the moment (i.e, do not pay attention on them) and focus on other pressing issues in wait stats or performance tuning. Here are two of my informal suggestions, which are totally independent from wait stats: Turn off the Full Text Search service in your system if you are  not necessarily using it on your server. Learn proper Full Text Search methodology. You can get Michael Coles’ book: Pro Full-Text Search in SQL Server 2008. Now I invite you to speak out your suggestions or any input regarding Full Text-related best practices and wait stats issue. Please leave a comment. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• SQL SERVER – SSMS: Memory Usage By Memory Optimized Objects Report

  - by Pinal Dave

  At conferences and at speaking engagements at the local UG, there is one question that keeps on coming which I wish were never asked. The question around, “Why is SQL Server using up all the memory and not releasing even when idle?” Well, the answer can be long and with the release of SQL Server 2014, this got even more complicated. This release of SQL Server 2014 has the option of introducing In-Memory OLTP which is completely new concept and our dependency on memory has increased multifold. In reality, nothing much changes but we have memory optimized objects (Tables and Stored Procedures) additional which are residing completely in memory and improving performance. As a DBA, it is humanly impossible to get a hang of all the innovations and the new features introduced in the next version. So today’s blog is around the report added to SSMS which gives a high level view of this new feature addition. This reports is available only from SQL Server 2014 onwards because the feature was introduced in SQL Server 2014. Earlier versions of SQL Server Management Studio would not show the report in the list. If we try to launch the report on the database which is not having In-Memory File group defined, then we would see the message in report. To demonstrate, I have created new fresh database called MemoryOptimizedDB with no special file group. Here is the query used to identify whether a database has memory-optimized file group or not. SELECT TOP(1) 1 FROM sys.filegroups FG WHERE FG.[type] = 'FX' Once we add filegroup using below command, we would see different version of report. USE [master] GO ALTER DATABASE [MemoryOptimizedDB] ADD FILEGROUP [IMO_FG] CONTAINS MEMORY_OPTIMIZED_DATA GO The report is still empty because we have not defined any Memory Optimized table in the database.  Total allocated size is shown as 0 MB. Now, let’s add the folder location into the filegroup and also created few in-memory tables. We have used the nomenclature of IMO to denote “InMemory Optimized” objects. USE [master] GO ALTER DATABASE [MemoryOptimizedDB] ADD FILE ( NAME = N'MemoryOptimizedDB_IMO', FILENAME = N'E:\Program Files\Microsoft SQL Server\MSSQL12.SQL2014\MSSQL\DATA\MemoryOptimizedDB_IMO') TO FILEGROUP [IMO_FG] GO You may have to change the path based on your SQL Server configuration. Below is the script to create the table. USE MemoryOptimizedDB GO --Drop table if it already exists. IF OBJECT_ID('dbo.SQLAuthority','U') IS NOT NULL DROP TABLE dbo.SQLAuthority GO CREATE TABLE dbo.SQLAuthority ( ID INT IDENTITY NOT NULL, Name CHAR(500)  COLLATE Latin1_General_100_BIN2 NOT NULL DEFAULT 'Pinal', CONSTRAINT PK_SQLAuthority_ID PRIMARY KEY NONCLUSTERED (ID), INDEX hash_index_sample_memoryoptimizedtable_c2 HASH (Name) WITH (BUCKET_COUNT = 131072) ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA) GO As soon as above script is executed, table and index both are created. If we run the report again, we would see something like below. Notice that table memory is zero but index is using memory. This is due to the fact that hash index needs memory to manage the buckets created. So even if table is empty, index would consume memory. More about the internals of how In-Memory indexes and tables work will be reserved for future posts. Now, use below script to populate the table with 10000 rows INSERT INTO SQLAuthority VALUES (DEFAULT) GO 10000 Here is the same report after inserting 1000 rows into our InMemory table.    There are total three sections in the whole report. Total Memory consumed by In-Memory Objects Pie chart showing memory distribution based on type of consumer – table, index and system. Details of memory usage by each table. The information about all three is taken from one single DMV, sys.dm_db_xtp_table_memory_stats This DMV contains memory usage statistics for both user and system In-Memory tables. If we query the DMV and look at data, we can easily notice that the system tables have negative object IDs.  So, to look at user table memory usage, below is the over-simplified version of query. USE MemoryOptimizedDB GO SELECT OBJECT_NAME(OBJECT_ID), * FROM sys.dm_db_xtp_table_memory_stats WHERE OBJECT_ID > 0 GO This report would help DBA to identify which in-memory object taking lot of memory which can be used as a pointer for designing solution. I am sure in future we will discuss at lengths the whole concept of In-Memory tables in detail over this blog. To read more about In-Memory OLTP, have a look at In-Memory OLTP Series at Balmukund’s Blog. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL Tagged: SQL Memory, SQL Reports

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• binary search tree recursive subtree in java

  - by Art Peterson

  Can anyone point me to a code example (java preferably) or psuedocode that uses recursion to return a subtree that contains all nodes with keys between fromKey and toKey. So if I was to call Tree.subtree(5,10) it should return all nodes in the BST that have keys between 5 and 10 inclusive - but I can't use loops or helper methods...only recursive calls to the subtree method, which takes fromKey and toKey as parameters. Thanks!

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• SQL SERVER – SSMS: Backup and Restore Events Report

  - by Pinal Dave

  A DBA wears multiple hats and in fact does more than what an eye can see. One of the core task of a DBA is to take backups. This looks so trivial that most developers shrug this off as the only activity a DBA might be doing. I have huge respect for DBA’s all around the world because even if they seem cool with all the scripting, automation, maintenance works round the clock to keep the business working almost 365 days 24×7, their worth is knowing that one day when the systems / HDD crashes and you have an important delivery to make. So these backup tasks / maintenance jobs that have been done come handy and are no more trivial as they might seem to be as considered by many. So the important question like: “When was the last backup taken?”, “How much time did the last backup take?”, “What type of backup was taken last?” etc are tricky questions and this report lands answers to the same in a jiffy. So the SSMS report, we are talking can be used to find backups and restore operation done for the selected database. Whenever we perform any backup or restore operation, the information is stored in the msdb database. This report can utilize that information and provide information about the size, time taken and also the file location for those operations. Here is how this report can be launched.   Once we launch this report, we can see 4 major sections shown as listed below. Average Time Taken For Backup Operations Successful Backup Operations Backup Operation Errors Successful Restore Operations Let us look at each section next. Average Time Taken For Backup Operations Information shown in “Average Time Taken For Backup Operations” section is taken from a backupset table in the msdb database. Here is the query and the expanded version of that particular section USE msdb; SELECT (ROW_NUMBER() OVER (ORDER BY t1.TYPE))%2 AS l1 ,       1 AS l2 ,       1 AS l3 ,       t1.TYPE AS [type] ,       (AVG(DATEDIFF(ss,backup_start_date, backup_finish_date)))/60.0 AS AverageBackupDuration FROM backupset t1 INNER JOIN sys.databases t3 ON ( t1.database_name = t3.name) WHERE t3.name = N'AdventureWorks2014' GROUP BY t1.TYPE ORDER BY t1.TYPE On my small database the time taken for differential backup was less than a minute, hence the value of zero is displayed. This is an important piece of backup operation which might help you in planning maintenance windows. Successful Backup Operations Here is the expanded version of this section.   This information is derived from various backup tracking tables from msdb database.  Here is the simplified version of the query which can be used separately as well. SELECT * FROM sys.databases t1 INNER JOIN backupset t3 ON (t3.database_name = t1.name) LEFT OUTER JOIN backupmediaset t5 ON ( t3.media_set_id = t5.media_set_id) LEFT OUTER JOIN backupmediafamily t6 ON ( t6.media_set_id = t5.media_set_id) WHERE (t1.name = N'AdventureWorks2014') ORDER BY backup_start_date DESC,t3.backup_set_id,t6.physical_device_name; The report does some calculations to show the data in a more readable format. For example, the backup size is shown in KB, MB or GB. I have expanded first row by clicking on (+) on “Device type” column. That has shown me the path of the physical backup file. Personally looking at this section, the Backup Size, Device Type and Backup Name are critical and are worth a note. As mentioned in the previous section, this section also has the Duration embedded inside it. Backup Operation Errors This section of the report gets data from default trace. You might wonder how. One of the event which is tracked by default trace is “ErrorLog”. This means that whatever message is written to errorlog gets written to default trace file as well. Interestingly, whenever there is a backup failure, an error message is written to ERRORLOG and hence default trace. This section takes advantage of that and shows the information. We can read below message under this section, which confirms above logic. No backup operations errors occurred for (AdventureWorks2014) database in the recent past or default trace is not enabled. Successful Restore Operations This section may not be very useful in production server (do you perform a restore of database?) but might be useful in the development and log shipping secondary environment, where we might be interested to see restore operations for a particular database. Here is the expanded version of the section. To fill this section of the report, I have restored the same backups which were taken to populate earlier sections. Here is the simplified version of the query used to populate this output. USE msdb; SELECT * FROM restorehistory t1 LEFT OUTER JOIN restorefile t2 ON ( t1.restore_history_id = t2.restore_history_id) LEFT OUTER JOIN backupset t3 ON ( t1.backup_set_id = t3.backup_set_id) WHERE t1.destination_database_name = N'AdventureWorks2014' ORDER BY restore_date DESC,  t1.restore_history_id,t2.destination_phys_name Have you ever looked at the backup strategy of your key databases? Are they in sync and do we have scope for improvements? Then this is the report to analyze after a week or month of maintenance plans running in your database. Do chime in with what are the strategies you are using in your environments. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL Tagged: SQL Reports

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• SQL SERVER – Concurrency Basics – Guest Post by Vinod Kumar

  - by pinaldave

  This guest post is by Vinod Kumar. Vinod Kumar has worked with SQL Server extensively since joining the industry over a decade ago. Working on various versions from SQL Server 7.0, Oracle 7.3 and other database technologies – he now works with the Microsoft Technology Center (MTC) as a Technology Architect. Let us read the blog post in Vinod’s own voice. Learning is always fun when it comes to SQL Server and learning the basics again can be more fun. I did write about Transaction Logs and recovery over my blogs and the concept of simplifying the basics is a challenge. In the real world we always see checks and queues for a process – say railway reservation, banks, customer supports etc there is a process of line and queue to facilitate everyone. Shorter the queue higher is the efficiency of system (a.k.a higher is the concurrency). Every database does implement this using checks like locking, blocking mechanisms and they implement the standards in a way to facilitate higher concurrency. In this post, let us talk about the topic of Concurrency and what are the various aspects that one needs to know about concurrency inside SQL Server. Let us learn the concepts as one-liners: Concurrency can be defined as the ability of multiple processes to access or change shared data at the same time. The greater the number of concurrent user processes that can be active without interfering with each other, the greater the concurrency of the database system. Concurrency is reduced when a process that is changing data prevents other processes from reading that data or when a process that is reading data prevents other processes from changing that data. Concurrency is also affected when multiple processes are attempting to change the same data simultaneously. Two approaches to managing concurrent data access: Optimistic Concurrency Model Pessimistic Concurrency Model Concurrency Models Pessimistic Concurrency Default behavior: acquire locks to block access to data that another process is using. Assumes that enough data modification operations are in the system that any given read operation is likely affected by a data modification made by another user (assumes conflicts will occur). Avoids conflicts by acquiring a lock on data being read so no other processes can modify that data. Also acquires locks on data being modified so no other processes can access the data for either reading or modifying. Readers block writer, writers block readers and writers. Optimistic Concurrency Assumes that there are sufficiently few conflicting data modification operations in the system that any single transaction is unlikely to modify data that another transaction is modifying. Default behavior of optimistic concurrency is to use row versioning to allow data readers to see the state of the data before the modification occurs. Older versions of the data are saved so a process reading data can see the data as it was when the process started reading and not affected by any changes being made to that data. Processes modifying the data is unaffected by processes reading the data because the reader is accessing a saved version of the data rows. Readers do not block writers and writers do not block readers, but, writers can and will block writers. Transaction Processing A transaction is the basic unit of work in SQL Server. Transaction consists of SQL commands that read and update the database but the update is not considered final until a COMMIT command is issued (at least for an explicit transaction: marked with a BEGIN TRAN and the end is marked by a COMMIT TRAN or ROLLBACK TRAN). Transactions must exhibit all the ACID properties of a transaction. ACID Properties Transaction processing must guarantee the consistency and recoverability of SQL Server databases. Ensures all transactions are performed as a single unit of work regardless of hardware or system failure. A – Atomicity C – Consistency I – Isolation D- Durability Atomicity: Each transaction is treated as all or nothing – it either commits or aborts. Consistency: ensures that a transaction won’t allow the system to arrive at an incorrect logical state – the data must always be logically correct.  Consistency is honored even in the event of a system failure. Isolation: separates concurrent transactions from the updates of other incomplete transactions. SQL Server accomplishes isolation among transactions by locking data or creating row versions. Durability: After a transaction commits, the durability property ensures that the effects of the transaction persist even if a system failure occurs. If a system failure occurs while a transaction is in progress, the transaction is completely undone, leaving no partial effects on data. Transaction Dependencies In addition to supporting all four ACID properties, a transaction might exhibit few other behaviors (known as dependency problems or consistency problems). Lost Updates: Occur when two processes read the same data and both manipulate the data, changing its value and then both try to update the original data to the new value. The second process might overwrite the first update completely. Dirty Reads: Occurs when a process reads uncommitted data. If one process has changed data but not yet committed the change, another process reading the data will read it in an inconsistent state. Non-repeatable Reads: A read is non-repeatable if a process might get different values when reading the same data in two reads within the same transaction. This can happen when another process changes the data in between the reads that the first process is doing. Phantoms: Occurs when membership in a set changes. It occurs if two SELECT operations using the same predicate in the same transaction return a different number of rows. Isolation Levels SQL Server supports 5 isolation levels that control the behavior of read operations. Read Uncommitted All behaviors except for lost updates are possible. Implemented by allowing the read operations to not take any locks, and because of this, it won’t be blocked by conflicting locks acquired by other processes. The process can read data that another process has modified but not yet committed. When using the read uncommitted isolation level and scanning an entire table, SQL Server can decide to do an allocation order scan (in page-number order) instead of a logical order scan (following page pointers). If another process doing concurrent operations changes data and move rows to a new location in the table, the allocation order scan can end up reading the same row twice. Also can happen if you have read a row before it is updated and then an update moves the row to a higher page number than your scan encounters later. Performing an allocation order scan under Read Uncommitted can cause you to miss a row completely – can happen when a row on a high page number that hasn’t been read yet is updated and moved to a lower page number that has already been read. Read Committed Two varieties of read committed isolation: optimistic and pessimistic (default). Ensures that a read never reads data that another application hasn’t committed. If another transaction is updating data and has exclusive locks on data, your transaction will have to wait for the locks to be released. Your transaction must put share locks on data that are visited, which means that data might be unavailable for others to use. A share lock doesn’t prevent others from reading but prevents them from updating. Read committed (snapshot) ensures that an operation never reads uncommitted data, but not by forcing other processes to wait. SQL Server generates a version of the changed row with its previous committed values. Data being changed is still locked but other processes can see the previous versions of the data as it was before the update operation began. Repeatable Read This is a Pessimistic isolation level. Ensures that if a transaction revisits data or a query is reissued the data doesn’t change. That is, issuing the same query twice within a transaction cannot pickup any changes to data values made by another user’s transaction because no changes can be made by other transactions. However, this does allow phantom rows to appear. Preventing non-repeatable read is a desirable safeguard but cost is that all shared locks in a transaction must be held until the completion of the transaction. Snapshot Snapshot Isolation (SI) is an optimistic isolation level. Allows for processes to read older versions of committed data if the current version is locked. Difference between snapshot and read committed has to do with how old the older versions have to be. It’s possible to have two transactions executing simultaneously that give us a result that is not possible in any serial execution. Serializable This is the strongest of the pessimistic isolation level. Adds to repeatable read isolation level by ensuring that if a query is reissued rows were not added in the interim, i.e, phantoms do not appear. Preventing phantoms is another desirable safeguard, but cost of this extra safeguard is similar to that of repeatable read – all shared locks in a transaction must be held until the transaction completes. In addition serializable isolation level requires that you lock data that has been read but also data that doesn’t exist. Ex: if a SELECT returned no rows, you want it to return no. rows when the query is reissued. This is implemented in SQL Server by a special kind of lock called the key-range lock. Key-range locks require that there be an index on the column that defines the range of values. If there is no index on the column, serializable isolation requires a table lock. Gets its name from the fact that running multiple serializable transactions at the same time is equivalent of running them one at a time. Now that we understand the basics of what concurrency is, the subsequent blog posts will try to bring out the basics around locking, blocking, deadlocks because they are the fundamental blocks that make concurrency possible. Now if you are with me – let us continue learning for SQL Server Locking Basics. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Concurrency

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• SQL SERVER – Puzzle to Win Print Book – Explain Value of PERCENTILE_CONT() Using Simple Example

  - by pinaldave

  From last several days I am working on various Denali Analytical functions and it is indeed really fun to refresh the concept which I studied in the school. Earlier I wrote article where I explained how we can use PERCENTILE_CONT() to find median over here SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012. Today I am going to ask question based on the same blog post. Again just like last time the intention of this puzzle is as following: Learn new concept of SQL Server 2012 Learn new concept of SQL Server 2012 even if you are on earlier version of SQL Server. On another note, SQL Server 2012 RC0 has been announced and available to download SQL SERVER – 2012 RC0 Various Resources and Downloads. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: The reason we get median is because we are passing value .05 to PERCENTILE_COUNT() function. Now run read the puzzle. Puzzle: Run following T-SQL code: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.9) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO Observe the result and you will notice that MidianCont has different value than before, the reason is PERCENTILE_CONT function has 0.9 value passed. For first four value the value is 775.1. Now run following T-SQL code: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.1) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO Observe the result and you will notice that MidianCont has different value than before, the reason is PERCENTILE_CONT function has 0.1 value passed. For first four value the value is 709.3. Now in my example I have explained how the median is found using this function. You have to explain using mathematics and explain (in easy words) why the value in last columns are 709.3 and 775.1 Hint: SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012 Rules Leave a comment with your detailed answer by Nov 25's blog post. Open world-wide (where Amazon ships books) If you blog about puzzle’s solution and if you win, you win additional surprise gift as well. Prizes Print copy of my new book SQL Server Interview Questions Amazon|Flipkart If you already have this book, you can opt for any of my other books SQL Wait Stats [Amazon|Flipkart|Kindle] and SQL Programming [Amazon|Flipkart|Kindle]. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Solution – Puzzle – SELECT * vs SELECT COUNT(*)

  - by pinaldave

  Earlier I have published Puzzle Why SELECT * throws an error but SELECT COUNT(*) does not. This question have received many interesting comments. Let us go over few of the answers, which are valid. Before I start the same, let me acknowledge Rob Farley who has not only answered correctly very first but also started interesting conversation in the same thread. The usual question will be what is the right answer. I would like to point to official Microsoft Connect Items which discusses the same. RGarvao https://connect.microsoft.com/SQLServer/feedback/details/671475/select-test-where-exists-select tiberiu utan http://connect.microsoft.com/SQLServer/feedback/details/338532/count-returns-a-value-1 Rob Farley count(*) is about counting rows, not a particular column. It doesn’t even look to see what columns are available, it’ll just count the rows, which in the case of a missing FROM clause, is 1. “select *” is designed to return columns, and therefore barfs if there are none available. Even more odd is this one: select ‘blah’ where exists (select *) You might be surprised at the results… Koushik The engine performs a “Constant scan” for Count(*) where as in the case of “SELECT *” the engine is trying to perform either Index/Cluster/Table scans. amikolaj When you query ‘select * from sometable’, SQL replaces * with the current schema of that table. With out a source for the schema, SQL throws an error. so when you query ‘select count(*)’, you are counting the one row. * is just a constant to SQL here. Check out the execution plan. Like the description states – ‘Scan an internal table of constants.’ You could do ‘select COUNT(‘my name is adam and this is my answer’)’ and get the same answer. Netra Acharya SELECT * Here, * represents all columns from a table. So it always looks for a table (As we know, there should be FROM clause before specifying table name). So, it throws an error whenever this condition is not satisfied. SELECT COUNT(*) Here, COUNT is a Function. So it is not mandetory to provide a table. Check it out this: DECLARE @cnt INT SET @cnt = COUNT(*) SELECT @cnt SET @cnt = COUNT(‘x’) SELECT @cnt Naveen Select 1 / Select ‘*’ will return 1/* as expected. Select Count(1)/Count(*) will return the count of result set of select statement. Count(1)/Count(*) will have one 1/* for each row in the result set of select statement. Select 1 or Select ‘*’ result set will contain only 1 result. so count is 1. Where as “Select *” is a sysntax which expects the table or equauivalent to table (table functions, etc..). It is like compilation error for that query. Ramesh Hi Friends, Count is an aggregate function and it expects the rows (list of records) for a specified single column or whole rows for *. So, when we use ‘select *’ it definitely give and error because ‘*’ is meant to have all the fields but there is not any table and without table it can only raise an error. So, in the case of ‘Select Count(*)’, there will be an error as a record in the count function so you will get the result as ’1'. Try using : Select COUNT(‘RAMESH’) and think there is an error ‘Must specify table to select from.’ in place of ‘RAMESH’ Pinal : If i am wrong then please clarify this. Sachin Nandanwar Any aggregate function expects a constant or a column name as an expression. DO NOT be confused with * in an aggregate function.The aggregate function does not treat it as a column name or a set of column names but a constant value, as * is a key word in SQL. You can replace any value instead of * for the COUNT function.Ex Select COUNT(5) will result as 1. The error resulting from select * is obvious it expects an object where it can extract the result set. I sincerely thank you all for wonderful conversation, I personally enjoyed it and I am sure all of you have the same feeling. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: CodeProject, Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• Linq-to-sql Compiled Query returns object NOT belonging to submitted DataContext ?

  - by Vladimir Kojic

  Compiled query: public static class Machines { public static readonly Func<OperationalDataContext, short, Machine> QueryMachineById = CompiledQuery.Compile((OperationalDataContext db, short machineID) => db.Machines.Where(m => m.MachineID == machineID).SingleOrDefault() ); public static Machine GetMachineById(IUnitOfWork unitOfWork, short id) { Machine machine; // Old code (working) //var machineRepository = unitOfWork.GetRepository<Machine>(); //machine = machineRepository.Find(m => m.MachineID == id).SingleOrDefault(); // New code (making problems) machine = QueryMachineById(unitOfWork.DataContext, id); return machine; } It looks like compiled query is returning result from another data context [TestMethod] public void GetMachinesTest() { using (var unitOfWork = IoC.Get<IUnitOfWork>()) { // Compile Query var machine = Machines.GetMachineById(unitOfWork, 3); } using (var unitOfWork = IoC.Get<IUnitOfWork>()) { var machineRepository = unitOfWork.GetRepository<Machine>(); // Get From Repository var machineFromRepository = machineRepository.Find(m => m.MachineID == 2).SingleOrDefault(); var machine = Machines.GetMachineById(unitOfWork, 2); VerifyHuskyHostMachine(machineFromRepository, 2, "Machine 2", "222222", "H400RS", "MachineIconB.xaml", false, true, LicenseType.Licensed, InterfaceType.HuskyHostV2, "10.0.97.2:8080", "10.0.97.2", 8080, "4.0"); VerifyHuskyHostMachine(machine, 2, "Machine 2", "222222", "H400RS", "MachineIconB.xaml", false, true, LicenseType.Licensed, InterfaceType.HuskyHostV2, "10.0.97.2:8080", "10.0.97.2", 8080, "4.0"); Assert.AreSame(machineFromRepository, machine); // FAIL } } If I run other (complex) unit tests I'm getting as expected: An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. Another Important information is that this test is under TransactionScope! UPDATE: It looks like next link is describing similar problem (is this bug solved ?): http://social.msdn.microsoft.com/Forums/en-US/linqprojectgeneral/thread/9bcffc2d-794e-4c4a-9e3e-cdc89dad0e38

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• How do I break down MySQL query results into categories, each with a specific number of rows?

  - by Mel

  Hello, Problem: I want to list n number of games from each genre (order not important) The following MySQL query resides inside a ColdFusion function. It is meant to list all games under a platform (for example, list all PS3 games; list all Xbox 360 games; etc...). The variable for PlatformID is passed through the URL. I have 9 genres, and I would like to list 10 games from each genre. SELECT games.GameID AS GameID, games.GameReleaseDate AS rDate, titles.TitleName AS tName, titles.TitleShortDescription AS sDesc, genres.GenreName AS gName, platforms.PlatformID, platforms.PlatformName AS pName, platforms.PlatformAbbreviation AS pAbbr FROM (((games join titles on((games.TitleID = titles.TitleID))) join genres on((genres.GenreID = games.GenreID))) join platforms on((platforms.PlatformID = games.PlatformID))) WHERE (games.PlatformID = '#ARGUMENTS.PlatformID#') ORDER BY GenreName ASC, GameReleaseDate DESC Once the query results come back I group them in ColdFusion as follows: <cfoutput query="ListGames" group="gName"> (first loop which lists genres) #ListGames.gName# <cfoutput> (nested loop which lists games) #ListGames.tName# </cfoutput> </cfoutput> The problem is that I only want 10 games from each genre to be listed. If I place a "limit" of 50 in the SQL, I will get ~ 50 games of the same genre (depending on how much games of that genre there are). The second issue is I don't want the overload of querying the database for all games when each person will only look at a few. What is the correct way to do this? Many thanks!

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• SQL SERVER – SQLServer Quiz 2011 – Do you know your execution plan – Two questions – One Answer

  - by pinaldave

  My friend Jacob Sebastian has SQL Server Quiz 2011 launched. This time when he asked me to come up with quiz question – I wanted to come up with something which is new and make participant to think about it. After carefully thinking I come with question which I really like to solve myself. Here is the details: 1) Using Single table only Once in Single SELECT statement generate execution plan which have JOIN operator. Explain the reason for the same. 2) Using Single table only Once in Single SELECT statement generate execution plan which have parallelism operator. Explain the reason for the same. Bonus: Create a single query which satisfy both of the above statement. To answer this question and win exciting gifts please visit the SQL Server Quiz website. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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