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• sql server 2005 indexes and low cardinality

  - by Peanut

  How does SQL Server determine whether a table column has low cardinality? The reason I ask is because query optimizer would most probably not use an index on a gender column (values 'm' and 'f'). However how would it determine the cardinality of the gender column to come to that decision? On top of this, if in the unlikely event that I had a million entries in my table and only one entry in the gender column was 'm', would SQL server be able to determine this and use the index to retrieve that single row? Or would it just know there are only 2 distinct values in the column and not use the index? I appreciate the above discusses some poor db design, but I'm just trying to understand how query optimizer comes to its decisions. Many thanks.

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• Is it worth caching a Dictionary for foreign key values in ASP.net?

  - by user169867

  I have a Dictionary<int, string> cached (for 20 minutes) that has ~120 ID/Name pairs for a reference table. I iterate over this collection when populating dropdown lists and I'm pretty sure this is faster than querying the DB for the full list each time. My question is more about if it makes sense to use this cached dictionary when displaying records that have a foreign key into this reference table. Say this cached reference table is a EmployeeType table. If I were to query and display a list of employee names and types should I query for EmployeeName and EmployeeTypeID and use my cached dictionary to grab the EmployeeTypeIDs name as each record is displayed or is it faster to just have the DB grab the EmployeeName and JOIN to get the EmployeeType string bypassing the cached Dictionary all together. I know both will work but I'm interested in what will perform the fastest. Thanks for any help.

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• Problem with truncation of floating point values in DBSlayer.

  - by chrisdew

  When I run a query through DBslayer http://code.nytimes.com/projects/dbslayer the floating point results are truncated to a total of six digits (plus decimal point and negative sign when needed). { ... "lat":52.2228,"lng":-2.19906, ... } When I run the same query in MySQL, the results are as expected. | 52.22280884 | -2.19906425 | Firstly, am I correct in identifying DBSlayer as the cause of this effect? (Or the JSON library it uses, etc.) Secondly, is this floating point precision configurable within DBSlayer? Thanks, Chris. P.S. Ubuntu 9.10, x86_64 Path: . URL: http://dbslayer.googlecode.com/svn/trunk Repository Root: http://dbslayer.googlecode.com/svn Repository UUID: 5df2be84-4748-0410-afd4-f777a056bd0c Revision: 65 Node Kind: directory Schedule: normal Last Changed Author: dgottfrid Last Changed Rev: 65 Last Changed Date: 2008-03-28 22:52:46 +0000 (Fri, 28 Mar 2008)

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• SQL: select random row from table where the ID of the row isn't in another table?

  - by johnrl

  I've been looking at fast ways to select a random row from a table and have found the following site: http://74.125.77.132/search?q=cache:http://jan.kneschke.de/projects/mysql/order-by-rand/&hl=en&strip=1 What I want to do is to select a random url from my table 'urls' that I DON'T have in my other table 'urlinfo'.The query I am using now selects a random url from 'urls' but I need it modified to only return a random url that is NOT in the 'urlinfo' table. Heres the query: SELECT url FROM urls JOIN (SELECT CEIL(RAND() * (SELECT MAX(urlid) FROM urls ) ) AS urlid ) AS r2 USING(urlid); And the two tables: CREATE TABLE urls ( urlid INT NOT NULL AUTO_INCREMENT PRIMARY KEY, url VARCHAR(255) NOT NULL, ) ENGINE=INNODB; CREATE TABLE urlinfo ( urlid INT NOT NULL PRIMARY KEY, urlinfo VARCHAR(10000), FOREIGN KEY (urlid) REFERENCES urls (urlid) ) ENGINE=INNODB;

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• Efficiency of checking for null varbinary(max) column ?

  - by Moe Sisko

  Using SQL Server 2008. Example table : CREATE table dbo.blobtest (id int primary key not null, name nvarchar(200) not null, data varbinary(max) null) Example query : select id, name, cast((case when data is null then 0 else 1 end) as bit) as DataExists from dbo.blobtest Now, the query needs to return a "DataExists" column, that returns 0 if the blob is null, else 1. This all works fine, but I'm wondering how efficient it is. i.e. does SQL server need to read in the whole blob to its memory, or is there some optimization so that it just does enough reads to figure out if the blob is null or not ? (FWIW, the sp_tableoption "large value types out of row" option is set to OFF for this example).

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• How to Pass a JS Variable to a PHP Variable

  - by dmullins

  Hello: I am working on a web application that currently provides a list of documents in a MySql database. Each document in the list has an onclick event that is suppose to open the specific document, however I am unable to do this. My list gets popluated using Ajax. Here is the code excerpt (JS): function stateChanged() { if (xmlhttp.readyState==4) { //All documents// document.getElementById("screenRef").innerHTML="<font id='maintxt'; name='title'; onclick='fileopen()'; color='#666666';>" + xmlhttp.responseText + "</font>"; } } } The onclick=fileopen event above triggers the next code excerpt, which downloads the file (JS): function stateChanged() { if (xmlhttp.readyState==4) { //Open file var elemIF = document.createElement("iframe"); elemIF.src = url; elemIF.style.display = "none"; document.body.appendChild(elemIF); } } } Lastly, the openfile onclick event triggers the following php code to find the file for downloading (php): $con = mysql_connect("localhost", "root", "password"); if (!$con) { die('Could not connect: ' . mysql_error()); } mysql_select_db("Documents", $con); $query = mysql_query("SELECT name, type, size, content FROM upload WHERE name = NEED JS VARIABLE HERE"); $row = mysql_fetch_array($query); header ("Content-type: ". $row['type']); header ("Content-length: ". $row['size']); header ("Content-Disposition: attachement; filename=". $row['name']); echo $row['content']; This code works well, for downloading a file. If I omit the WHERE portion of the Sql query, the onclick event will download the first file. Somehow, I need to get the screenRef element text and change it into a variable that my php file can read. Does anyone know how to do this? Also, without any page refreshes. I really appreciate everyone's feedback and thank you in advance. DFM

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• How can I subsample data from a time series with LINQ to SQL?

  - by Chris Farmer

  I have a database table full of time points and experimental values at those time points. I need to retrieve the values for an experiment and create a thumbnail image showing an XY plot of its data. Because the actual data set for each experiment is potentially 100,000 data points and my image is only 100 pixels wide, I want to sample the data before creating the image. My current query (which retrieves all the data without sampling) is something simple like this: var points = from p in db.DataPoints where p.ExperimentId == myExperimentId orderby p.Time select new { X = p.Time, Y = p.Value } So, how can I best take every nth point from my result set in a LINQ to SQL query?

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• How to work with file and streams in php,case: if we open file in Class A and pass open stream to Cl

  - by Rachel

  I have two class, one is Business Logic Class{BLO} and the other one is Data Access Class{DAO} and I have dependency in my BLO class to my Dao class. Basically am opening a csv file to write into it in my BLO class using inside its constructor as I am creating an object of BLO and passing in file from command prompt: Code: $this->fin = fopen($file,'w+') or die('Cannot open file'); Now inside BLO I have one function notifiy, which call has dependency to DAO class and call getCurrentDBSnapshot function from the Dao and passes the open stream so that data gets populated into the stream. Code: Blo Class Constructor: public function __construct($file) { //Open Unica File for parsing. $this->fin = fopen($file,'w+') or die('Cannot open file'); // Initialize the Repository DAO. $this->dao = new Dao('REPO'); } Blo Class method that interacts with Dao Method and call getCurrentDBSnapshot. public function notifiy() { $data = $this->fin; var_dump($data); //resource(9) of type (stream) $outputFile=$this->dao->getCurrentDBSnapshot($data); // So basically am passing in $data which is resource((9) of type (stream) } Dao function: getCurrentDBSnapshot which get current state of Database table. public function getCurrentDBSnapshot($data) { $query = "SELECT * FROM myTable"; //Basically just preparing the query. $stmt = $this->connection->prepare($query); // Execute the statement $stmt->execute(); $header = array(); while ($row=$stmt->fetch(PDO::FETCH_ASSOC)) { if(empty($header)) { // Get the header values from table(columnnames) $header = array_keys($row); // Populate csv file with header information from the mytable fputcsv($data, $header); } // Export every row to a file fputcsv($data, $row); } var_dump($data);//resource(9) of type (stream) return $data; } So basically in am getting back resource(9) of type (stream) from getCurrentDBSnapshot and am storing that stream into $outputFile in Blo class method notify. Now I want to close the file which I opened for writing and so it should be fclose of $outputFile or $data, because in both the cases it gives me: var_dump(fclose($outputFile)) as bool(false) var_dump(fclose($data)) as bool(false) and var_dump($outputFile) as resource(9) of type (Unknown) var_dump($data) as resource(9) of type (Unknown) My question is that if I open file using fopen in class A and if I call class B method from Class A method and pass an open stream, in our case $data, than Class B would perform some work and return back and open stream and so How can I close that open stream in Class A's method or it is ok to keep that stream open and not use fclose ? Would appreciate inputs as am not very sure as how this can be implemented.

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• Best of OTN - Week of August 17th

  - by CassandraClark-OTN

  Architect CommunityThe Top 3 most popular OTN ArchBeat video interviews of all time: Oracle Coherence Community on Java.net | Brian Oliver and Randy Stafford [October 24, 2013] Brian Oliver (Senior Principal Solutions Architect, Oracle Coherence) and Randy Stafford (Architect At-Large, Oracle Coherence Product Development) discuss the evolution of the Oracle Coherence Community on Java.net and how developers can actively participate in product development through Coherence Community open projects. Visit the Coherence Community at: https://java.net/projects/coherence. The Raspberry Pi Java Carputer and Other Wonders | Simon Ritter [February 13, 2014] Oracle lead Java evangelist Simon Ritter talks about his Raspberry Pi-based Java Carputer IoT project and other topics he presented at QCon London 2014. Hot Features in Oracle APEX 5.0 | Joel Kallman [May 14, 2014] Joel Kallman (Director, Software Development, Oracle) shares key points from his Great Lakes Oracle Conference 2014 session on new features in Oracle APEX 5.0. Friday Funny from OTN Architect Community Manager Bob Rhubart: Comedy legend Steve Martin entertains dogs in this 1976 clip from the Carol Burnette show. Database Community OTN Database Community Home Page - See all tech articles, downloads etc. related to Oracle Database for DBA's and Developers. Java Community JavaOne Blog - JRuby and JVM Languages at JavaOne!  In this video interview, Charles shared the JRuby features he presented at the JVM Language Summit. He'll be at JavaOne read the blog to see all the sessions. Java Source Blog - IoT: Wearables! Wearables are a subset of the Internet of Things that has gained a lot of attention. Learn More. I love Java FaceBook - Java Advanced Management Console demo - Watch as Jim Weaver, Java Technology Ambassador at Oracle, walks through a demonstration of the new Java Advanced Management Console (AMC) tool. Systems Community OTN Garage Blog - Why Wouldn't Root Be Able to Change a Zone's IP Address in Oracle Solaris 11? - Read and learn the answer. OTN Garage FaceBook - Securing Your Cloud-Based Data Center with Oracle Solaris 11 - Overview of the security precautions a sysadmin needs to take to secure data in a cloud infrastructure, and how to implement them with the security features in Oracle Solaris 11.

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• Why would I do an inner join on a non-distinct field?

  - by froadie

  I just came across a query that does an inner join on a non-distinct field. I've never seen this before and I'm a little confused about this usage. Something like: SELECT distinct all, my, stuff FROM myTable INNER JOIN myOtherTable ON myTable.nonDistinctField = myOtherTable.nonDistinctField (WHERE some filters here...) I'm not quite sure what my question is or how to phrase it, or why exactly this confuses me, but I was wondering if anyone could explain why someone would need to do an inner join on a non-distinct field and then select only distinct values...? Is there ever a legitimate use of an inner join on a non-distinct field? What would be the purpose? And if there's is a legitimate reason for such a query, can you give examples of where it would be used?

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• Does SQL Server Compact Edition (SqlCe) have a SNAPSHOT table like Oracle Lite?

  - by MusiGenesis

  In Oracle Lite, you can create a SNAPSHOT table which is like a normal table except that it tracks changes to itself. The syntax is CREATE SNAPSHOT TABLE tblWhatever ... and you can perform CRUD operations on it like a normal table. To get the change information, you query the table like this: SELECT * FROM tblWhatever + WHERE ... which returns all the rows in the table (including deleted ones) meeting the WHERE clause, and you can access each row's row_state column as a normal field (which is invisible to a normal SELECT * FROM tblWhatever WHERE ... query). Is there some way to do the same thing with Sql Compact Edition (3.5) - i.e. create a table that tracks changes without using RDA?

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• iPhone OSStatus -25308 or errSecInteractionNotAllowed SFHFKeychainUtils

  - by George Octavio

  Hi again guys. I'm trying to access my iPhone's device keychain. I want to access in order to create a simple user-password value intended for a log in function. This is the code I'm using from SFHFKeychainUtils NSArray *keys = [[[NSArray alloc] initWithObjects: (NSString *) kSecClass, kSecAttrService, kSecAttrLabel, kSecAttrAccount, kSecValueData, nil] autorelease]; NSArray *objects = [[[NSArray alloc] initWithObjects: (NSString *) kSecClassGenericPassword, serviceName, serviceName, @"TestUser", @"TestPass", nil] autorelease]; NSDictionary *query = [[[NSDictionary alloc] initWithObjects: objects forKeys: keys] autorelease]; OSStatus status = SecItemAdd((CFDictionaryRef) query, NULL); } else if (status != noErr) { //Output to screen with error code goes here return NO; } return YES; } The error code I'm getting is OSStatus-25308 or errSecInteractionNotAllowed. I'm guessing this means I don't actually have access to my iPhone's keychain? Is there a way to allow access? Thanks for your time.

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• mysql birthday reminder, leap year

  - by moodh

  Hi, I'm trying to sort out a result set that gives the 5 closest users sorted by upcoming birthday. This works perfectly until leap years comes into play. For example: May 15th - 96 days left May 15th - 97 days left The top result is a birth at 1987 and the lower is from 1988. u_birth is stored as yyyy-mm-dd. Is there a simple way to sort this problem without having to rewrite the entire query? SELECT u_birth, IF( DAYOFYEAR( u_birth ) >= DAYOFYEAR( NOW() ), DAYOFYEAR( u_birth ) - DAYOFYEAR( NOW() ), DAYOFYEAR( u_birth ) - DAYOFYEAR( NOW() ) + DAYOFYEAR( CONCAT( YEAR( NOW() ), '-12-31' ) ) ) AS distance FROM (blog_users) WHERE `s_agehide` = 0 ORDER BY distance ASC LIMIT 5 This query is taken and modified from the mysql manual: http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#c7489

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• Declarative JDOQL vs Single-String JDOQL : performance

  - by DrDro

  When querying with JDOQL is there a performance difference between using the declarative version and the Single-String version: Example from the JDOQL doc: //Declarative JDOQL : Query q = pm.newQuery(org.jpox.Person.class, "lastName == \"Jones\" && age < age_limit"); q.declareParameters("double age_limit"); List results = (List)q.execute(20.0); //Single-String JDOQL : Query q = pm.newQuery("SELECT FROM org.jpox.Person WHERE lastName == \"Jones\"" + " && age < :age_limit PARAMETERS double age_limit"); List results = (List)q.execute(20.0); Other then performance, are there any reasons for which one is better to use then the other or is it just about the one with which we feel more comfortable.

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• Interesting SSMS issue with waittype of PREEMPTIVE_OS_LOOKUPACCOUNTSID

  - by steveh99999

  Saw a recent issue with SQL2008 sp 1 where SQL Server Management Studio (SSMS) appeared to hang when a DBA expanded the database users tab of a database… ie like this :-   When we looked at the waittype of the SSMS session - via sys.dm_os_waiting_tasks– it was waiting on PREEMPTIVE_OS_LOOKUPACCOUNTSID. I’d not come across this waittype before, and there was very little information out on the web for it.. Looking at this issue using SQL Profiler – it them became apparent that SSMS was waiting on the function SUSER_SNAME. I did a quick test using SET STATISTICS TIME to prove it was the SUSER_SNAME function causing our issue :- SELECT * FROM sys.database_principals   -- completes in 6 milliseconds SELECT SUSER_SNAME(sid),* FROM sys.database_principals  -- completes in 188941 milliseconds. suser_sname validates a sid against Active Directory.. What I haven’t mentioned so far is that the database in question had been restored from a server on a different domain. This domain was untrusted from the current domain. However, it appeared that SSMS was still trying to validate the Windows login of each user when displaying the users list…. and taking a long time to return NULL for each user from the untrusted domain. When all users that had a login from the untrusted domain are removed from the database – this fixed the issue. To find out the users that had this issue :- SELECT name FROM sys.database_principals WHERE type_desc IN(‘WINDOWS_USER’, ‘WINDOWS_GROUP’) and SUSER_SNAME(sid) IS NULL Although I have not raised this as a case with MS – I do think this is a bug in SSMS – I do not see why windows logins should need to be validated when displaying only user details..

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• SQL finding members who are not friends of another member

  - by thedirktastik

  I'm struggling to find a query which will return members who aren't friends of a certain member. Here is the layout of my tables: member_login: MemberID, email, password member_info: memberID, first_name, last_name member_friends: friendID, req_member, req_date, app_member, app_date, date_deactivated I tried to use NOT IN to run a query that would return the opposite of friends but nothing I try seems to be working. Here's what I thought would work: SELECT Mi.First_Name, Mi.Last_Name FROM Member_Info Mi WHERE Mi.Memberid NOT IN( SELECT Mi.Memberid, Mi.First_Name, Mi.Last_Name FROM Member_Info Mi, Member_Login Ml, Member_Friends Mf WHERE Mi.Memberid = Ml.Memberid AND (Mi.Memberid = Mf.Req_Member AND Mf.App_Member = 1 OR Mi.Memberid = Mf.App_Member AND Mf.Req_Member =1) AND Ml.Date_Deactivated <= 0 AND Mf.App_Date > 0 ); Any ideas?

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• hibernate order by association

  - by Gary Kephart

  I'm using Hibernate 3.2, and using criteria to build a query. I'd like to add and "order by" for a many-to-one association, but I don't see how that can be done. The Hibernate query would end up looking like this, I guess: select t1.a, t1.b, t1.c, t2.dd, t2.ee from t1 inner join t2 on t1.a = t2.aa order by t2.dd <-- need to add this I've tried criteria.addOrder("assnName.propertyName") but it doesn't work. I know it can be done for normal properties. Am I missing something?

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• SQL joins "going up" two tables

  - by blcArmadillo

  I'm trying to create a moderately complex query with joins: SELECT `history`.`id`, `parts`.`type_id`, `serialized_parts`.`serial`, `history_actions`.`action`, `history`.`date_added` FROM `history_actions`, `history` LEFT OUTER JOIN `parts` ON `parts`.`id` = `history`.`part_id` LEFT OUTER JOIN `serialized_parts` ON `serialized_parts`.`parts_id` = `history`.`part_id` WHERE `history_actions`.`id` = `history`.`action_id` AND `history`.`unit_id` = '1' ORDER BY `history`.`id` DESC I'd like to replace `parts`.`type_id` in the SELECT statement with `part_list`.`name` where the relationship I need to enforce between the two tables is `part_list`.`id` = `parts`.`type_id`. Also I have to use joins because in some cases `history`.`part_id` may be NULL which obviously isn't a valid part id. How would I modify the query to do this?

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• Best arguments for/against introducing ORM technology into a companies dev process

  - by james

  I have started using ORM technology in the last few years. My first exposure was NHibernate. I then moved onto Linq 2 Sql, and Entity Framework. The issue I have however is, there are some organisations where I have found strong opposition to introducing ORM tools. They usually have a number of reasons: they have a lot of built up SQL skills in the team, and are worried about the underlying SQL that ORM's generate. they have DBA's who like to be able to see the SQL an app uses in order that can review it for best practice. they are worried about performance (some people have "heard" the ORM's aren't as performant but have no real proof themselves - there may well be some truth in this! :). So, I'm looking for the best or most convincing arguments that you have put forward FOR the use of ORM tools. Equally, I would be interested in the against arguments too. Note: this is NOT a discussion over which ORM I should use.

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• Insert multiple values using INSERT INTO

  - by Ben McCormack

  In SQL Server 2005, I'm trying to figure out why I'm not able to insert multiple fields into a table. The following query, which inserts one record, works fine: INSERT INTO [MyDB].[dbo].[MyTable] ([FieldID] ,[Description]) VALUES (1000,N'test') However, the following query, which specifies more than one value, fails: INSERT INTO [MyDB].[dbo].[MyTable] ([FieldID] ,[Description]) VALUES (1000,N'test'),(1001,N'test2') I get this message: Msg 102, Level 15, State 1, Line 5 Incorrect syntax near ','. When I looked up the help for INSERT in SQL Sever Management Studio, one of their examples showed using the "Values" syntax that I used (with groups of values in parentheses and separated by commas). The help documentation I found in SQL Server Management Studio looks like it's for SQL Server 2008, so perhaps that's the reason that the insert doesn't work. Either way, I can't figure out why it won't work.

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• Django DecimalField returns "None" instead of empty value

  - by Ed

  Is there a way to force django to display nothing instead of "None" for a Decimal Field that's been left blank? In my template, I show a list of all the values for a particular field. Each value is hyperlinked to a page that displays the results of a query filtered on that value. But because there are some entries with null value, my list includes actual DecimalField entries and "None" for all those that are empty. When a user clicks on None, django throws a validation error because you cannot query a DecimalField using a string. I could write if statements checking all instances of decimal fields for Nones and skipping them, but that is far from an elegant solution. Any advice? This is one part of the code, though there are other templates that derive the None value in slightly different manners: {% for item in choices %} <a href={% url app_views.field_choice item %}>{{ item }}</a><br> {% endfor %}

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• dilemma about mysql. using condition to limit load on a dbf

  - by ondrobaco

  hi, I have a table of about 800 000 records. Its basically a log which I query often. I gave condition to query only queries that were entered last month in attempt to reduce the load on a database. My thinking is a) if the database goes only through the first month and then returns entries, its good. b) if the database goes through the whole database + checking the condition against every single record, it's actually worse than no condition. What is your opinion? How would you go about reducing load on a dbf?

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• default caching time when using hibernate

  - by cometta

  when using hibernate 2nd level cache and query cache and not specifying anything inside ehcache.xml .what is the default caching time?

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• SQL GROUP BY - also SELECT not-constant columns

  - by Michal Kosek

  can someone please help me with this query? I have 2 tables in my database: log_visitors: -------------------- id | host_id log_access: -------------------- visitor | document | timestamp "log_access.visitor" links to "log_visitors.id" Currently, I'm using this query: SELECT log_visitors.host_id , MIM(log_access.timestamp) AS min_timestamp FROM log_access INNER JOIN log_visitors ON (log_access.visitor = log_visitors.id) GROUP BY log_visitors.host_id; to get "MIN(timestamp)" for each "host_id" in the database. HERE'S MY QUESTION: I also need to get "document" for that access with that timestamp... I can't simply add "log_access.document" into SELECT list, since it's not constant and I am not grouping by document... Any ideas?

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• My father is a doctor. He is insisting on writing a database to store non-critical patient information, with no programming background

  - by Dominic Bou-Samra

  So, my father is currently in the process of "hacking" together a database using FileMaker Pro, a GUI based databasing tool for his small (4 doctor) practice. The database will be used to help ease the burden on reporting from medical machines, streamlining quite a clumsy process. He's got no programming background, and seems to be doing everything in his power to not learn things correctly. He's got duplicate data types, no database-enforced relationships (foreign/primary key constraints) and a dozen other issues. He's doing it all by hand via GUI tool using Youtube videos. My issue is, that whilst I want him to succeed 100%, I don't think it's appropriate for him to be handling these types of decisions. How do I convince him that without some sort of education in these topics, a hacked together solution is a bad idea? He's can be quite stubborn and I think he sees these types of jobs as "childs play" How should I approach this? Is it even that bad an idea - or am I correct in thinking he should hire a proper DBA/developer to handle this so that it doesn't become a maintenance nightmare? NB: I am a developer consultant of 4 years and I've seen my share of painful customer implementations.

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