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• Filter on count(*) in oracle

  - by chris

  I have a grouped query, and would like to filter it based on count(*) Can I do this without a subquery? This is what I have currently: select * from (select ID, count(*) cnt from name group by ID) where cnt > 1;

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• update multiple rows in oracle

  - by devang

  hi can you tell me how to update multiple rows in oracle as when i fired the update statment it gave me the following error ORA-01427: single-row subquery returns more than one row Thanks in advance

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• Transaction within IF THEN ELSE doesn't commit

  - by boris callens

  In my TSQL script I have an IF THEN ELSE structure that checks if a column already exists. If not it creates the column and updates it. IF NOT EXISTS( SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'tableName' AND COLUMN_NAME = 'columnName')) BEGIN BEGIN TRANSACTION ALTER TABLE tableName ADD columnName int NULL COMMIT BEGIN TRANSACTION update tableName set columnName = [something] from [subquery] COMMIT END This doesn't work because the column doesn't exist after the commit. Why doesn't the COMMIT commit?

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• MySql query BETWEEN two Strings sometimes doesn't work

  - by bucabay

  I have a mysql query where a subquery is: BETWEEN '5.00' AND '10.00' And this returns no results. However when I use Floats or Ints: BETWEEN 5 and 10 it works The BETWEEN query also works for other values AS strings, but just not for 5 and 10. EG: BETWEEN '4' AND '5' works. How could this be?

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• Update all table rows but top N in Mysql

  - by arthurprs

  I was trying to run the following query UPDATE blog_post SET `thumbnail_present`=0, `thumbnail_size`=0, `thumbnail_data`='' WHERE `blog_post` NOT IN ( SELECT `blog_post` FROM blog_post ORDER BY `blog_post` DESC LIMIT 10) But Mysql doesn't allow 'LIMIT' in an 'IN' subquery. I think I can make a select to count the table rows and then make an ordered update limited by 'COUNT - 10', but I was wondering if there is a better way. Thanks in advance.

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• Returning Null values with COUNT

  - by Randy B.

  With this query, I get a result that is two short of the table because they are not included in count, and I would like get the NULL values in the result. To do this, I am pretty sure I need to use a subquery of some kind, but I am not sure how, since the attribute in question is an aggregate. SELECT Equipment.SerialNo , Name, COUNT(Assignment.SerialNo) FROM Equipment INNER JOIN Assignment ON Assignment.SerialNo = Equipment.SerialNo GROUP BY Equipment.SerialNo, Name

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• Is it possible to get id of affected rows in MySQL?

  - by user198729

  I'm using pdo to do this : update tags set cnt=cnt-1 where name in ? delete from news_tag where news_id=? and tag_id in (select id from tags where name in ?) But if I can get affected rows' id,the subquery is not needed.

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• MySQL: How to do a conditional update?

  - by Tom

  Hi, I'm trying to a create an update statement along the following lines: TABLE car: id | owner_id | type | status An owner can have multiple cars. UPDATE car c SET c.type = 1 WHERE c.owner_id IN ($ids) AND c.status = [1 IF IT EXISTS, ELSE 0] $ids is reasonably small (under 50 values). It seems simple but I can't seem to get my head around it because I can't use a SELECT subquery with an UPDATE to the same table. Anyone? Thanks

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• How to connect two query results?

  - by nijansen

  I want to retrieve all ids within a certain timespan. The timestamps however, are stored in a different table: Table A has column my_id Table B has columns my_id, timestamp I would want something like SELECT id, time FROM (SELECT my_id AS id FROM A) q1, (SELECT timestamp AS time FROM B WHERE my_id = id) q2 ; But how can I get the value of id within a different subquery? Is there an elegant solution for this problem?

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• SQL SERVER – Weekly Series – Memory Lane – #032

  - by Pinal Dave

  Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 Complete Series of Database Coding Standards and Guidelines SQL SERVER Database Coding Standards and Guidelines – Introduction SQL SERVER – Database Coding Standards and Guidelines – Part 1 SQL SERVER – Database Coding Standards and Guidelines – Part 2 SQL SERVER Database Coding Standards and Guidelines Complete List Download Explanation and Example – SELF JOIN When all of the data you require is contained within a single table, but data needed to extract is related to each other in the table itself. Examples of this type of data relate to Employee information, where the table may have both an Employee’s ID number for each record and also a field that displays the ID number of an Employee’s supervisor or manager. To retrieve the data tables are required to relate/join to itself. Insert Multiple Records Using One Insert Statement – Use of UNION ALL This is very interesting question I have received from new developer. How can I insert multiple values in table using only one insert? Now this is interesting question. When there are multiple records are to be inserted in the table following is the common way using T-SQL. Function to Display Current Week Date and Day – Weekly Calendar Straight blog post with script to find current week date and day based on the parameters passed in the function.  2008 In my beginning years, I have almost same confusion as many of the developer had in their earlier years. Here are two of the interesting question which I have attempted to answer in my early year. Even if you are experienced developer may be you will still like to read following two questions: Order Of Column In Index Order of Conditions in WHERE Clauses Example of DISTINCT in Aggregate Functions Have you ever used DISTINCT with the Aggregation Function? Here is a simple example about how users can do it. Create a Comma Delimited List Using SELECT Clause From Table Column Straight to script example where I explained how to do something easy and quickly. Compound Assignment Operators SQL SERVER 2008 has introduced new concept of Compound Assignment Operators. Compound Assignment Operators are available in many other programming languages for quite some time. Compound Assignment Operators is operator where variables are operated upon and assigned on the same line. PIVOT and UNPIVOT Table Examples Here is a very interesting question – the answer to the question can be YES or NO both. “If we PIVOT any table and UNPIVOT that table do we get our original table?” Read the blog post to get the explanation of the question above. 2009 What is Interim Table – Simple Definition of Interim Table The interim table is a table that is generated by joining two tables and not the final result table. In other words, when two tables are joined they create an interim table as resultset but the resultset is not final yet. It may be possible that more tables are about to join on the interim table, and more operations are still to be applied on that table (e.g. Order By, Having etc). Besides, it may be possible that there is no interim table; sometimes final table is what is generated when the query is run. 2010 Stored Procedure and Transactions If Stored Procedure is transactional then, it should roll back complete transactions when it encounters any errors. Well, that does not happen in this case, which proves that Stored Procedure does not only provide just the transactional feature to a batch of T-SQL. Generate Database Script for SQL Azure When talking about SQL Azure the most common complaint I hear is that the script generated from stand-along SQL Server database is not compatible with SQL Azure. This was true for some time for sure but not any more. If you have SQL Server 2008 R2 installed you can follow the guideline below to generate a script which is compatible with SQL Azure. Convert IN to EXISTS – Performance Talk It is NOT necessary that every time when IN is replaced by EXISTS it gives better performance. However, in our case listed above it does for sure give better performance. You can read about this subject in the associated blog post. Subquery or Join – Various Options – SQL Server Engine Knows the Best Every single time whenever there is a performance tuning exercise, I hear the conversation from developer where some prefer subquery and some prefer join. In this two part blog post, I explain the same in the detail with examples. Part 1 | Part 2 Merge Operations – Insert, Update, Delete in Single Execution MERGE is a new feature that provides an efficient way to do multiple DML operations. In earlier versions of SQL Server, we had to write separate statements to INSERT, UPDATE, or DELETE data based on certain conditions; however, at present, by using the MERGE statement, we can include the logic of such data changes in one statement that even checks when the data is matched and then just update it, and similarly, when the data is unmatched, it is inserted. 2011 Puzzle – Statistics are not updated but are Created Once Here is the quick scenario about my setup. Create Table Insert 1000 Records Check the Statistics Now insert 10 times more 10,000 indexes Check the Statistics – it will be NOT updated – WHY? Question to You – When to use Function and When to use Stored Procedure Personally, I believe that they are both different things - they cannot be compared. I can say, it will be like comparing apples and oranges. Each has its own unique use. However, they can be used interchangeably at many times and in real life (i.e., production environment). I have personally seen both of these being used interchangeably many times. This is the precise reason for asking this question. 2012 In year 2012 I had two interesting series ran on the blog. If there is no fun in learning, the learning becomes a burden. For the same reason, I had decided to build a three part quiz around SEQUENCE. The quiz was to identify the next value of the sequence. I encourage all of you to take part in this fun quiz. Guess the Next Value – Puzzle 1 Guess the Next Value – Puzzle 2 Guess the Next Value – Puzzle 3 Guess the Next Value – Puzzle 4 Simple Example to Configure Resource Governor – Introduction to Resource Governor Resource Governor is a feature which can manage SQL Server Workload and System Resource Consumption. We can limit the amount of CPU and memory consumption by limiting /governing /throttling on the SQL Server. If there are different workloads running on SQL Server and each of the workload needs different resources or when workloads are competing for resources with each other and affecting the performance of the whole server resource governor is a very important task. Tricks to Replace SELECT * with Column Names – SQL in Sixty Seconds #017 – Video  Retrieves unnecessary columns and increases network traffic When a new columns are added views needs to be refreshed manually Leads to usage of sub-optimal execution plan Uses clustered index in most of the cases instead of using optimal index It is difficult to debug SQL SERVER – Load Generator – Free Tool From CodePlex The best part of this SQL Server Load Generator is that users can run multiple simultaneous queries again SQL Server using different login account and different application name. The interface of the tool is extremely easy to use and very intuitive as well. A Puzzle – Swap Value of Column Without Case Statement Let us assume there is a single column in the table called Gender. The challenge is to write a single update statement which will flip or swap the value in the column. For example if the value in the gender column is ‘male’ swap it with ‘female’ and if the value is ‘female’ swap it with ‘male’. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Oracle analytic functions for "the attribute from the row with the max date"

  - by tpdi

  I'm refactoring a colleague's code, and I have several cases where he's using a cursor to get "the latest row that matches some predicate": His technique is to write the join as a cursor, order it by the date field descending, open the cursor, get the first row, and close the cursor. This requires calling a cursor for each row of the result set that drives this, which is costly for many rows. I'd prefer to be able to join, but what something cheaper than a correlated subquery: select a.id_shared_by_several_rows, a.foo from audit_trail a where a.entry_date = (select max(a.entry_date) from audit_trail b where b.id_shared_by_several_rows = a.id_shared_by_several_rows ); I'm guessing that since this is a common need, there's an Oracle analytic function that does this?

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• Oracle analytic functions for "the atatrbute from the row with the max date"

  - by tpdi

  I'm refactoring a colleague's code, and I have several cases where he's using a cursor to get "the latest row that matches some predicate": His technique is to write the join as a cursor, order it by the date field descending, open the cursor, get the first row, and close the cursor. This requires calling a cursor for each row of the result set that drives this, which is costly for many rows. I'd prefer to be able to join, but what something cheaper than a correlated subquery: select a.id_shared_by_several_rows, a.foo from audit_trail a where a.entry_date = (select max(a.entry_date) from audit_trail b where b.id_shared_by_several_rows = a.id_shared_by_several_rows ); I'm guessing that since this is a common need, there's an Oracle analytic function that does this?

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• Optimal Sharing of heavy computation job using Snow and/or multicore

  - by James

  Hi, I have the following problem. First my environment, I have two 24-CPU servers to work with and one big job (resampling a large dataset) to share among them. I've setup multicore and (a socket) Snow cluster on each. As a high-level interface I'm using foreach. What is the optimal sharing of the job? Should I setup a Snow cluster using CPUs from both machines and split the job that way (i.e. use doSNOW for the foreach loop). Or should I use the two servers separately and use multicore on each server (i.e. split the job in two chunks, run them on each server and then stich it back together). Basically what is an easy way to: 1. Keep communication between servers down (since this is probably the slowest bit). 2. Ensure that the random numbers generated in the servers are not highly correlated.

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• Calculating probability that a string has been randomized? - Python

  - by RadiantHex

  Hi folks, this is correlated to a question I asked earlier (question) I have a list of manually created strings such as: lucy87 gordan_king fancy_unicorn77 joplucky_kanga90 base_belong_to_narwhals and a list of randomized strings: johnkdf pancake90kgjd fancy_jagookfk manhattanljg What gives away that the last set of strings are randomized is that sequences such as 'kjg', 'jgf', 'lkd', ... . Any clever way I could separate strings that contain these apparently randomized strings from the crowd? I guess that this plays a lot on the fact that certain characters are more likely to be placed next to others (e.g. 'co', 'ka', 'ja', ...). Any ideas on this one? Kylotan mentioned Reverend, but I am not sure if it can be used fr such purpose. Help would be much appreciated!

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• Can I use SQL to update multiple rows with multiple values from another table?

  - by stu

  I've got a one to many table with ids and traits for those users. I want to copy one user's settings to another. userid trait onoff ------ ----- ----- 1 1 on 1 2 on 1 3 on 1 4 on 2 1 off 2 2 off 2 3 off 2 4 off So I want to copy the onoff values from user 1 to 2, so that user2 has everything on when I'm done. update table set onoff = (select onoff from table where userid=1) where userid=2 that's the basic idea, but obviously doesn't work. I imagine I want the server to think in terms of a correlated subquery, but the outer part isn't a query, it's an update. Is this even possible in one step?

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• Get/save parameters to an expected JMock method call?

  - by Tayeb

  Hi, I want to test an "Adapter" object that when it receives an xml message, it digest it to a Message object, puts message ID + CorrelationID both with timestamps and forwards it to a Client object.=20 A message can be correlated to a previous one (e.g. m2.correlationID =3D m1.ID). I mock the Client, and check that Adapter successfully calls "client.forwardMessage(m)" twice with first message with null correlationID, and a second with a not-null correlationID. However, I would like to precisely test that the correlationIDs are set correctly, by grabing the IDs (e.g. m1.ID). But I couldn't find anyway to do so. There is a jira about adding the feature, but no one commented and it is unassigned. Is this really unimplemented? I read about the alternative of redesigning the Adapter to use an IdGenerator object, which I can stub, but I think there will be too many objects.=20 Don't you think it adds unnecessary complexity to split objects to a so fine granularity? Thanks, and I appreciate any comments :-) Tayeb

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• Where to add an observer to the NotificationCenter in a UITableViewController

  - by Saifis

  I want to send a notification from a UITableViewController-A to UITableViewController-B. I was adding the observer in the initwithCoder of the UITableViewController that is supposed to catch the notifications. The classes are correlated as folows RootViewController ===NavigationController-A =====UITableViewController-A ===NavigationController-B =====UITableViewController-B I need to add the observer before the views are actually loaded because notifications may be sent before the view is called. However I have been told that initializing in the initWithCoder method in a UIViewController is not advisable, and was told to add the observer in the AppDelegate. Are there any other suggestions for doing this?

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• javascript - how to control if /else if / else

  - by Fernando SBS

  How to control to which if the else is correlated? ex: if X = 1 { // A if Y > 1 { // B gothere(); } } else if X < 1 { // C gohere(); } else { // D gonowhere(); } how to make sure C and D will not be related to B??? here´s another example: if xxx { ... FM_log(7,"vList.length = "+vList.length); if (skippingAvancado) if (vList.length > 1) changeVillage(); else { if (skipcounter >= maxSkipCount) { FM_log(7,"ROTINA ANTIGA SKIPCOUNTER"); changeVillage(); } } else {

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• Top 5 Developer Enabling Nuggets in MySQL 5.6

  - by Rob Young

  MySQL 5.6 is truly a better MySQL and reflects Oracle's commitment to the evolution of the most popular and widelyused open source database on the planet.  The feature-complete 5.6 release candidate was announced at MySQL Connect in late September and the production-ready, generally available ("GA") product should be available in early 2013.  While the message around 5.6 has been focused mainly on mass appeal, advanced topics like performance/scale, high availability, and self-healing replication clusters, MySQL 5.6 also provides many developer-friendly nuggets that are designed to enable those who are building the next generation of web-based and embedded applications and services. Boiling down the 5.6 feature set into a smaller set, of simple, easy to use goodies designed with developer agility in mind, these things deserve a quick look:Subquery Optimizations Using semi-JOINs and late materialization, the MySQL 5.6 Optimizer delivers greatly improved subquery performance. Specifically, the optimizer is now more efficient in handling subqueries in the FROM clause; materialization of subqueries in the FROM clause is now postponed until their contents are needed during execution. Additionally, the optimizer may add an index to derived tables during execution to speed up row retrieval. Internal tests run using the DBT-3 benchmark Query #13, shown below, demonstrate an order of magnitude improvement in execution times (from days to seconds) over previous versions. select c_name, c_custkey, o_orderkey, o_orderdate, o_totalprice, sum(l_quantity)from customer, orders, lineitemwhere o_orderkey in (                select l_orderkey                from lineitem                group by l_orderkey                having sum(l_quantity) > 313  )  and c_custkey = o_custkey  and o_orderkey = l_orderkeygroup by c_name, c_custkey, o_orderkey, o_orderdate, o_totalpriceorder by o_totalprice desc, o_orderdateLIMIT 100;What does this mean for developers?  For starters, simplified subqueries can now be coded instead of complex joins for cross table lookups: SELECT title FROM film WHERE film_id IN (SELECT film_id FROM film_actor GROUP BY film_id HAVING count(*) > 12); And even more importantly subqueries embedded in packaged applications no longer need to be re-written into joins.  This is good news for both ISVs and their customers who have access to the underlying queries and who have spent development cycles writing, testing and maintaining their own versions of re-written queries across updated versions of a packaged app.The details are in the MySQL 5.6 docs. Online DDL OperationsToday's web-based applications are designed to rapidly evolve and adapt to meet business and revenue-generationrequirements. As a result, development SLAs are now most often measured in minutes vs days or weeks. For example, when an application must quickly support new product lines or new products within existing product lines, the backend database schema must adapt in kind, and most commonly while the application remains available for normal business operations.  MySQL 5.6 supports this level of online schema flexibility and agility by providing the following new ALTER TABLE online DDL syntax additions:  CREATE INDEX DROP INDEX Change AUTO_INCREMENT value for a column ADD/DROP FOREIGN KEY Rename COLUMN Change ROW FORMAT, KEY_BLOCK_SIZE for a table Change COLUMN NULL, NOT_NULL Add, drop, reorder COLUMN Again, the details are in the MySQL 5.6 docs. Key-value access to InnoDB via Memcached APIMany of the next generation of web, cloud, social and mobile applications require fast operations against simple Key/Value pairs. At the same time, they must retain the ability to run complex queries against the same data, as well as ensure the data is protected with ACID guarantees. With the new NoSQL API for InnoDB, developers have allthe benefits of a transactional RDBMS, coupled with the performance capabilities of Key/Value store.MySQL 5.6 provides simple, key-value interaction with InnoDB data via the familiar Memcached API.  Implemented via a new Memcached daemon plug-in to mysqld, the new Memcached protocol is mapped directly to the native InnoDB API and enables developers to use existing Memcached clients to bypass the expense of query parsing and go directly to InnoDB data for lookups and transactional compliant updates.  The API makes it possible to re-use standard Memcached libraries and clients, while extending Memcached functionality by integrating a persistent, crash-safe, transactional database back-end.  The implementation is shown here:So does this option provide a performance benefit over SQL?  Internal performance benchmarks using a customized Java application and test harness show some very promising results with a 9X improvement in overall throughput for SET/INSERT operations:You can follow the InnoDB team blog for the methodology, implementation and internal test cases that generated these results here. How to get started with Memcached API to InnoDB is here. New Instrumentation in Performance SchemaThe MySQL Performance Schema was introduced in MySQL 5.5 and is designed to provide point in time metrics for key performance indicators.  MySQL 5.6 improves the Performance Schema in answer to the most common DBA and Developer problems.  New instrumentations include: Statements/Stages What are my most resource intensive queries? Where do they spend time? Table/Index I/O, Table Locks Which application tables/indexes cause the most load or contention? Users/Hosts/Accounts Which application users, hosts, accounts are consuming the most resources? Network I/O What is the network load like? How long do sessions idle? Summaries Aggregated statistics grouped by statement, thread, user, host, account or object. The MySQL 5.6 Performance Schema is now enabled by default in the my.cnf file with optimized and auto-tune settings that minimize overhead (< 5%, but mileage will vary), so using the Performance Schema ona production server to monitor the most common application use cases is less of an issue.  In addition, new atomic levels of instrumentation enable the capture of granular levels of resource consumption by users, hosts, accounts, applications, etc. for billing and chargeback purposes in cloud computing environments.The MySQL docs are an excellent resource for all that is available and that can be done with the 5.6 Performance Schema. Better Condition Handling - GET DIAGNOSTICSMySQL 5.6 enables developers to easily check for error conditions and code for exceptions by introducing the new MySQL Diagnostics Area and corresponding GET DIAGNOSTICS interface command. The Diagnostic Area can be populated via multiple options and provides 2 kinds of information:Statement - which provides affected row count and number of conditions that occurredCondition - which provides error codes and messages for all conditions that were returned by a previous operation The addressable items for each are: The new GET DIAGNOSTICS command provides a standard interface into the Diagnostics Area and can be used via the CLI or from within application code to easily retrieve and handle the results of the most recent statement execution.  An example of how it is used might be:mysql> DROP TABLE test.no_such_table; ERROR 1051 (42S02): Unknown table 'test.no_such_table' mysql> GET DIAGNOSTICS CONDITION 1 -> @p1 = RETURNED_SQLSTATE, @p2 = MESSAGE_TEXT; mysql> SELECT @p1, @p2; +-------+------------------------------------+| @p1   | @p2                                | +-------+------------------------------------+| 42S02 | Unknown table 'test.no_such_table' | +-------+------------------------------------+ Options for leveraging the MySQL Diagnotics Area and GET DIAGNOSTICS are detailed in the MySQL Docs.While the above is a summary of some of the key developer enabling 5.6 features, it is by no means exhaustive. You can dig deeper into what MySQL 5.6 has to offer by reading this developer zone article or checking out "What's New in MySQL 5.6" in the MySQL docs.BONUS ALERT!  If you are developing on Windows or are considering MySQL as an alternative to SQL Server for your next project, application or shipping product, you should check out the MySQL Installer for Windows.  The installer includes the MySQL 5.6 RC database, all drivers, Visual Studio and Excel plugins, tray monitor and development tools all a single download and GUI installer.   So what are your next steps? Register for Dec. 13 "MySQL 5.6: Building the Next Generation of Web-Based Applications and Services" live web event.  Hurry!  Seats are limited. Download the MySQL 5.6 Release Candidate (look under the Development Releases tab) Provide Feedback <link to http://bugs.mysql.com/> Join the Developer discussion on the MySQL Forums Explore all MySQL Products and Developer Tools As always, thanks for your continued support of MySQL!

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• Is there any way to send a column value from outer query to inner sub query? [closed]

  - by chetan

  'Discussions' table schema title description desid replyto upvote downvote views browser used a1 none 1 1 12 - bad topic b2 a1 2 3 14 sql database a3 none 4 5 34 - crome b4 a3 3 4 12 The above table has two types of content types Main Topics and Comments. Unique content identifier 'desid' used to identify that its a main topic or a comment. 'desid' starts with 'a' for Main Topic and for comment 'desid' starts with 'b'. For comment 'replyto' is the 'desid' of main topic to which this comment is associated. I like to find out the list of the top main topics that are arranged on the basis of (upvote+downvote+visits+number of comments to it) addition. The following query gives top topics list in order of (upvote+downvote+visits) select * with highest number of upvote+downvote+views by query "select * from [DB_user1212].[dbo].[discussions] where desid like 'a%' order by (upvote+downvote+visited) desc For (comments+upvote+downvote+views ) I tried select * from [DB_user1212].[dbo].[discussions] where desid like 'a%' order by ((select count(*) from [DB_user1212].[dbo].[discussions] where replyto = desid )+upvote+downvote+visited) desc but it didn't work because its not possible to send desid from outer query to inner subquery. How to solve this? Please note that I want solution in query language only.

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• What relational database system should I learn? [closed]

  - by acidzombie24

  At the moment i know sqlite (my favorite), mysql (its ok, i get annoyed) and i do not want to learn ms/t sql (it only allows one nullable row if the column is unique). I am thinking about learning a new database system. My requirements for it is Must allow multiple connections at once (read and write) All or data i choose must be ACID compliant Performance should be good. I have a 17gb table in one project. It should perform well on read and transactional writes. With mysql it took hours to restore it and there were no foreign keys on that specific table. It only finished in a workday because i found a suggestion to adjust a setting which i think was key-buffer. And it still took hours Unique columns that allow more then one row to be null. I shouldn't have to say it but dammit MS. Allows one to make ongoing backups. Something like 'binary logs'. Some relatively small amounts of data i can grab and apply it to my local db to have it in sync with the one on the server. Table joins. I rather not write a bunch of queries to simulate a join What I would like but is not required Foreign keys. This may be a requirement later Open sourced Fair tool support. So i can measure queries, easily backup/restore, etc .NET and C (or C++) interface. (I seen one that uses raw tcp with JSON which was okish) Good subquery support. Once i was working with an older version of mysql (i believe <5.1 but it could have been 5.1) and i had to write many queries to do one query because it couldn't do subqueries. Or maybe it couldnt do it efficiently and died bc of memory limitations with a huge dataset. What db system should i learn?

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• Why is SQLite3 using covering indices instead of the indices I created?

  - by Geoff

  I have an extremely large database (contacts has ~3 billion entries, people has ~280 million entries, and the other tables have a negligible number of entries). Most other queries I've run are really fast. However, I've encountered a more complicated query that's really slow. I'm wondering if there's any way to speed this up. First of all, here is my schema: CREATE TABLE activities (id INTEGER PRIMARY KEY, name TEXT NOT NULL); CREATE TABLE contacts ( id INTEGER PRIMARY KEY, person1_id INTEGER NOT NULL, person2_id INTEGER NOT NULL, duration REAL NOT NULL, -- hours activity_id INTEGER NOT NULL -- FOREIGN_KEY(person1_id) REFERENCES people(id), -- FOREIGN_KEY(person2_id) REFERENCES people(id) ); CREATE TABLE people ( id INTEGER PRIMARY KEY, state_id INTEGER NOT NULL, county_id INTEGER NOT NULL, age INTEGER NOT NULL, gender TEXT NOT NULL, -- M or F income INTEGER NOT NULL -- FOREIGN_KEY(state_id) REFERENCES states(id) ); CREATE TABLE states ( id INTEGER PRIMARY KEY, name TEXT NOT NULL, abbreviation TEXT NOT NULL ); CREATE INDEX activities_name_index on activities(name); CREATE INDEX contacts_activity_id_index on contacts(activity_id); CREATE INDEX contacts_duration_index on contacts(duration); CREATE INDEX contacts_person1_id_index on contacts(person1_id); CREATE INDEX contacts_person2_id_index on contacts(person2_id); CREATE INDEX people_age_index on people(age); CREATE INDEX people_county_id_index on people(county_id); CREATE INDEX people_gender_index on people(gender); CREATE INDEX people_income_index on people(income); CREATE INDEX people_state_id_index on people(state_id); CREATE INDEX states_abbreviation_index on states(abbreviation); CREATE INDEX states_name_index on states(name); Note that I've created an index on every column in the database. I don't care about the size of the database; speed is all I care about. Here's an example of a query that, as expected, runs almost instantly: SELECT count(*) FROM people, states WHERE people.state_id=states.id and states.abbreviation='IA'; Here's the troublesome query: SELECT * FROM contacts WHERE rowid IN (SELECT contacts.rowid FROM contacts, people, states WHERE contacts.person1_id=people.id AND people.state_id=states.id AND states.name='Kansas' INTERSECT SELECT contacts.rowid FROM contacts, people, states WHERE contacts.person2_id=people.id AND people.state_id=states.id AND states.name='Missouri'); Now, what I think would happen is that each subquery would use each relevant index I've created to speed this up. However, when I show the query plan, I see this: sqlite> EXPLAIN QUERY PLAN SELECT * FROM contacts WHERE rowid IN (SELECT contacts.rowid FROM contacts, people, states WHERE contacts.person1_id=people.id AND people.state_id=states.id AND states.name='Kansas' INTERSECT SELECT contacts.rowid FROM contacts, people, states WHERE contacts.person2_id=people.id AND people.state_id=states.id AND states.name='Missouri'); 0|0|0|SEARCH TABLE contacts USING INTEGER PRIMARY KEY (rowid=?) (~25 rows) 0|0|0|EXECUTE LIST SUBQUERY 1 2|0|2|SEARCH TABLE states USING COVERING INDEX states_name_index (name=?) (~1 rows) 2|1|1|SEARCH TABLE people USING COVERING INDEX people_state_id_index (state_id=?) (~5569556 rows) 2|2|0|SEARCH TABLE contacts USING COVERING INDEX contacts_person1_id_index (person1_id=?) (~12 rows) 3|0|2|SEARCH TABLE states USING COVERING INDEX states_name_index (name=?) (~1 rows) 3|1|1|SEARCH TABLE people USING COVERING INDEX people_state_id_index (state_id=?) (~5569556 rows) 3|2|0|SEARCH TABLE contacts USING COVERING INDEX contacts_person2_id_index (person2_id=?) (~12 rows) 1|0|0|COMPOUND SUBQUERIES 2 AND 3 USING TEMP B-TREE (INTERSECT) In fact, if I show the query plan for the first query I posted, I get this: sqlite> EXPLAIN QUERY PLAN SELECT count(*) FROM people, states WHERE people.state_id=states.id and states.abbreviation='IA'; 0|0|1|SEARCH TABLE states USING COVERING INDEX states_abbreviation_index (abbreviation=?) (~1 rows) 0|1|0|SEARCH TABLE people USING COVERING INDEX people_state_id_index (state_id=?) (~5569556 rows) Why is SQLite using covering indices instead of the indices I created? Shouldn't the search in the people table be able to happen in log(n) time given state_id which in turn is found in log(n) time?

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• Tips on ensuring Model Quality

  - by [email protected]

  Given enough data that represents well the domain and models that reflect exactly the decision being optimized, models usually provide good predictions that ensure lift. Nevertheless, sometimes the modeling situation is less than ideal. In this blog entry we explore the problems found in a few such situations and how to avoid them.1 - The Model does not reflect the problem you are trying to solveFor example, you may be trying to solve the problem: "What product should I recommend to this customer" but your model learns on the problem: "Given that a customer has acquired our products, what is the likelihood for each product". In this case the model you built may be too far of a proxy for the problem you are really trying to solve. What you could do in this case is try to build a model based on the result from recommendations of products to customers. If there is not enough data from actual recommendations, you could use a hybrid approach in which you would use the [bad] proxy model until the recommendation model converges.2 - Data is not predictive enoughIf the inputs are not correlated with the output then the models may be unable to provide good predictions. For example, if the input is the phase of the moon and the weather and the output is what car did the customer buy, there may be no correlations found. In this case you should see a low quality model.The solution in this case is to include more relevant inputs.3 - Not enough cases seenIf the data learned does not include enough cases, at least 200 positive examples for each output, then the quality of recommendations may be low. The obvious solution is to include more data records. If this is not possible, then it may be possible to build a model based on the characteristics of the output choices rather than the choices themselves. For example, instead of using products as output, use the product category, price and brand name, and then combine these models.4 - Output leaking into input giving the false impression of good quality modelsIf the input data in the training includes values that have changed or are available only because the output happened, then you will find some strong correlations between the input and the output, but these strong correlations do not reflect the data that you will have available at decision (prediction) time. For example, if you are building a model to predict whether a web site visitor will succeed in registering, and the input includes the variable DaysSinceRegistration, and you learn when this variable has already been set, you will probably see a big correlation between having a Zero (or one) in this variable and the fact that registration was successful.The solution is to remove these variables from the input or make sure they reflect the value as of the time of decision and not after the result is known. 

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• Read access to Active Directory property (uSNCreated)

  - by Tom Ligda

  I have an issue with read access to the uSNCreated property when doing LDAP searches. If I do an LDAP search with a user that is a member of the Domain Admins group (UserA), I can see the uSNCreated property for every user. The problem is that if I do an LDAP search with a user (UserB) that is not a member of the Domain Admins group, I can see the uSNCreated property for some users (UserGroupA) and not for some users (UserGroupB). When I look at the users in UserGroupA and compare them to the users in UserGroupB, I see a crucial difference in the "Security" tab. The users in UserGroupA have the "Include inheritable permissions from this object's parent" unchecked. The users in UserGroupB have that option checked. I also noticed that the users in UserGroupA are users that were created earlier. The users in UserGroupB are users created recently. It's difficult to quantify, but I estimate the border between creation time between the users in UserGroupA and UserGroupB is about 6 months ago. What can cause the user creation to default to having that security property checked as opposed to unchecked? A while back (maybe around 6 months ago?) I changed the domain functional level from Windows Server 2003 to Windows Server 2008 R2. Would that have had this effect? (I can't exactly downgrade the domain functional level to test it out.) Is this security property actually the cause of the issue with read access to the uSNChanged property on LDAP searches? It seems correlated, but I'm not sure about causation. What I want in the end is for all authenticated users to have read access to the uSNCreated property for all users when doing an LDAP search. I would also be OK if I could grant read access for that property to an AD group. Then I can control access by adding members to the group.

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• Plone site randomly serving wrong content

  - by Chris Miller

  I have a Plone site that has begun to randomly serve up the wrong content. Any given content suddenly shows something else. Sometimes a JPEG loads a stylesheet instead or a stylesheet loads as a page or a page as an image. The images move around, some times our site logo shows a bullet, or one of the other site images. Fiddler shows the wrong content in the response, the apache logs show the content type of the incorrect file (so if the an image loads in place of a style sheet, apache shows that). We thought mod_proxy was the source of our grief, but we get the problem hitting Zope directly. I never get the wrong content using the Medusa Monitor to repeatedly hit the content. I do see ConflictErrors in the instance.log file, and they seem to be correlated to the problem, but not 100%. ZPublisher.Conflict ConflictError at \path\to\object: database conflict error (oid 0x3586, class BTrees._OIBTree.OIBTree, serial this txn started with blah, serial currently committed blah) (X conflicts (0 unresolved) since startup blah) I pulled that off the web, it's not from our logs, but it's the same message. This may be a red herring, it sounds like those messages are normal. We've updated to the 3.3.5, same problems. I'm at a loss. I'm wondering if there a good way to intercept what is being served? Secondly, is there a way to increase the verbosity of the access log to included the content-type? I've even seen the problem manifest in ZMI. It happens more often when we're authenticated. Sometimes it can take a thousand reloads to see the problem, other times it happens in different ways every time we reload. I believe we've seen this problem for a couple years, but it was very intermittent, a page would show the content of a GIF, then a reload later wouldn't happen for a long time. Now it's a huge problem.

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