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• Most efficient way to rebuild a tree structure from data

  - by Ahsan

  Have a question on recursively populating JsTree using the .NET wrapper available via NuGet. Any help would be greatly appreciated. the .NET class JsTree3Node has a property named Children which holds a list of JsTree3Nodes, and the pre-existing table which contains the node structure looks like this NodeId ParentNodeId Data AbsolutePath 1 NULL News /News 2 1 Financial /News/Financial 3 2 StockMarket /News/Financial/StockMarket I have a EF data context from the the database, so my code currently looks like this. var parentNode = new JsTree3Node(Guid.NewGuid().ToString()); foreach(var nodeItem in context.Nodes) { parentNode.Children.Add(nodeItem.Data); // What is the most efficient logic to do this recursively? } as the inline comment says in the above code, what would be the most efficient way to load the JStree data on to the parentNode object. I can change the existing node table to suite the logic so feel free to suggest any changes to improve performance.

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• Efficiently representing a dynamic transform hierarchy

  - by Mattia

  I'm looking for a way to represent a dynamic transform hierarchy (i.e. one where nodes can be inserted and removed arbitrarily) that's a bit more efficient than using a standard tree of pointers . I saw the answers to this question ( Efficient structure for representing a transform hierarchy. ), but as far as I can determine the tree-as-array approach only works for static hierarchies or dynamic ones where nodes have a fixed number of children (both deal-breakers for me). I'm probably wrong about that but could anyone point out how? If I'm not wrong are there other alternatives that work for dynamic hierarchies?

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• Faking Display tree (Sprite) parent child relationships with rasters (BitmapData) in ActionScript 3

  - by Arthur Wulf White

  I am working with Rasters (bitmapData) and blliting (copypixels) in a 2d-game in actionscript 3. I like how you can move a sprite and it moves all it's children, and you can simultaneously move the children creating an interesting visual effect. I do not want to use rotation or scaling however cause I do not know how that can be done without hampering with performance. So I'm not simulating Sprite parent-child behavior and sticking to the movement on the (x, y) axis. What I am planning to do is create a class called RasterContainer which extends bitmapData that has a vector of children of type Raster(extending bitmapData), now I am planning to implement recursive rendering in RasterContainer, that basically copyPixels every child, only changing their (x, y) offset to reflect their parent's offset. My question is, has this been implemented in an existing framework? Is this a good plan? Do I expect a serious performance hit for using recursive methods this way?

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• Programming Language Family Tree?

  - by user134353

  As a man interested in programming, I must ask if there is a cataloged hierarchy of languages. I'd like to learn to actually understand what's happening- that is to say, I don't want to use a compiler until I understand what a compiler does and how to make my own. I really do want to start from total scratch. I'm told that means "machine code"? I don't know. What I do know is that "C++" is not the start. I'm not interested in learning that until I can actually break software down to its very base and see how the pieces go together.

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• Trinary Tree : algorithm for word list storage

  optimized algorithm for spell-checker-like database

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• Case Insensitive Ternary Search Tree

  - by Yan Cheng CHEOK

  I had been using Ternary Search Tree for a while, as the data structure to implement a auto complete drop down combo box. Which means, when user type "fo", the drop down combo box will display foo food football The problem is, my current used of Ternary Search Tree is case sensitive. My implementation is as follow. It had been used by real world for around 1++ yeas. Hence, I consider it as quite reliable. My Ternary Search Tree code However, I am looking for a case insensitive Ternary Search Tree, which means, when I type "fo", the drop down combo box will show me foO Food fooTBall Here are some key interface for TST, where I hope the new case insentive TST may have similar interface too. /** * Stores value in the TernarySearchTree. The value may be retrieved using key. * @param key A string that indexes the object to be stored. * @param value The object to be stored in the tree. */ public void put(String key, E value) { getOrCreateNode(key).data = value; } /** * Retrieve the object indexed by key. * @param key A String index. * @return Object The object retrieved from the TernarySearchTree. */ public E get(String key) { TSTNode<E> node = getNode(key); if(node==null) return null; return node.data; } An example of usage is as follow. TSTSearchEngine is using TernarySearchTree as the core backbone. Example usage of Ternary Search Tree // There is stock named microsoft and MICROChip inside stocks ArrayList. TSTSearchEngine<Stock> engine = TSTSearchEngine<Stock>(stocks); // I wish it would return microsoft and MICROCHIP. Currently, it just return microsoft. List<Stock> results = engine.searchAll("micro");

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• Flex Tree with infinite parents and children

  - by Tempname

  I am working on a tree component and I am having a bit of the issue with populating the data-provider for this tree. The data that I get back from my database is a simple array of value objects. Each value object has 2 properties. ObjectID and ParentID. For parents the ParentID is null and for children the ParentID is the ObjectID of the parent. Any help with this is greatly appreciated. Essentially the tree should look something like this: Parent1 Child1 Child1 Child2 Child1 Child2 Parent2 Child1 Child2 Child3 Child1 This is the current code that I am testing with: public function setDataProvider(data:Array):void { var tree:Array = new Array(); for(var i:Number = 0; i < data.length; i++) { // do the top level array if(!data[i].parentID) { tree.push(data[i], getChildren(data[i].objectID, data)); } } function getChildren(objectID:Number, data:Array):Array { var childArr:Array = new Array(); for(var k:Number = 0; k < data.length; k++) { if(data[k].parentID == objectID) { childArr.push(data[k]); //getChildren(data[k].objectID, data); } } return childArr; } trace(ObjectUtil.toString(tree)); } Here is a cross section of my data: ObjectID ParentID 1 NULL 10 NULL 8 NULL 6 NULL 4 6 3 6 9 6 2 6 11 7 7 8 5 8

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• How do I output the preorder traversal of a tree given the inorder and postorder tranversal?

  - by user342580

  Given the code for outputing the postorder traversal of a tree when I have the preorder and the inorder traversal in an interger array. How do I similarily get the preorder with the inorder and postorder array given? void postorder( int preorder[], int prestart, int inorder[], int inostart, int length) { if(length==0) return; //terminating condition int i; for(i=inostart; i<inostart+length; i++) if(preorder[prestart]==inorder[i])//break when found root in inorder array break; postorder(preorder, prestart+1, inorder, inostart, i-inostart); postorder(preorder, prestart+i-inostart+1, inorder, i+1, length-i+inostart-1); cout<<preorder[prestart]<<" "; } Here is the prototype for preorder() void preorder( int inorderorder[], int inostart, int postorder[], int poststart, int length)

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• How can I do block-oriented disk I/O with Java? Or similar for a B+ tree

  - by Sanoj

  I would like to implement an B+ tree in Java and try to optimize it for disk based I/O. Is there an API for accessing individual disk blocks from Java? or is there an API that can do similar block-oriented access that fits my purpose? I would like to create something like Tokyo Cabinet in 100% Java. Is there anyone that knows what Java only databases like JavaDB is using in the back-end for this? I know that there are probably other languages than Java that can do this better, but I do this in a learning purpose only.

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• How can I save a directory tree to an array in PHP?

  - by Greg

  I'm trying to take a directory with the structure: top folder1 file1 folder2 file1 file2 And save it into an array like: array ( 'folder1' => array('file1'), 'folder2' => array('file1', 'file2') ) This way, I can easily resuse the tree throughout my site. I've been playing around with this code but it's still not doing what I want: private function get_tree() { $uploads = __RELPATH__ . DS . 'public' . DS . 'uploads'; $iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($uploads), RecursiveIteratorIterator::SELF_FIRST); $output = array(); foreach($iterator as $file) { $relativePath = str_replace($uploads . DS, '', $file); if ($file->isDir()) { if (!in_array($relativePath, $output)) $output[$relativePath] = array(); } } return $output; }

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• HTML Markup in einem APEX Tree - ganz einfach per Plugin!

  - by carstenczarski

  Die APEX Tree Region kennt sicherlich jeder APEX-Entwickler. Und vielfach besteht der Bedarf, das Aussehen des APEX Tree mit Hilfe von HTML Markup zu beeinflussen. Leider ist es seit APEX 4.0 nicht mehr möglich, eigenes HTML-Markup in einen APEX-Tree aufzunehmen - aus Sicherheitsgründen (Schutz vor Cross-Site-Scripting) werden alle HTML Sonderzeichen maskiert. Wenn kein XSS-Risiko besteht (die vom Tree dargestellten Inhalte basieren nicht auf Benutzereingaben und werden komplett vom Entwickler bestimmt), kann dies mit wenigen Zeilen JavaScript und jQuery-Code erreicht werden. Damit es noch einfacher wird,  haben wir die Funktionalität für Sie in einem APEX-Plugin gekapselt. Und so funktioniert es: APEX Plugin "HTML Markup for APEX Tree Region" herunterladenhttp://apex-plugin.com/oracle-apex-plugins/dynamic-action-plugin/html-markup-for-apex-tree_174.html APEX Plugin in die Anwendung importieren APEX Tree Region erzeugen und eigene Ersetzungen für HTML-Sonderzeichen verwenden, also bspw."[" für "<", "]" für ">" und "§" für "&". Eine neue dynamische Aktion erzeugen, die beim Laden der Seite ausgeführt wird und mit Hilfe des Plugins die Ersetzungen im Tree durch die "richtigen" HTML-Sonderzeichen ersetzt. Fertig. Wie das Plugin wirkt, können Sie sich auf einer Demo-Seite ansehen.

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• Tool to compute SHA256 Tree Hash

  - by Benjamin

  I've started using AWS Glacier, and noticed that it hashes the files using an algorithm called SHA-256 Tree Hash. To my surprise, this algorithm is different from SHA-256, so I can't use the tools I'm used to, to compare hashes and verify file integrity. Do you know a Windows tool, if possible integrated in the context menu, to compute the SHA-256 Tree Hash of a file? I'd also accept a Linux command-line tool, as a second choice :-)

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• Binary Search Tree in C

  - by heapzero

  Hi, I'm a Python guy. Learning C language and I've been trying to implement Binary Search Tree in C. I wrote down the code, and I've been trying from few hours but, not able to get the output as expected. Please help! Please correct me. #include<stdlib.h> #include<stdio.h> typedef int ElementType; typedef struct TreeNode { ElementType element; struct TreeNode *left, *right; } TreeNode; TreeNode *createTree(){ //Create the root of tree TreeNode *tempNode; tempNode = malloc(sizeof(TreeNode)); tempNode->element = 0; tempNode->left = NULL; tempNode->right = NULL; return tempNode; } TreeNode *createNode(ElementType X){ //Create a new leaf node and return the pointer TreeNode *tempNode; tempNode = malloc(sizeof(TreeNode)); tempNode->element = X; tempNode->left = NULL; tempNode->right = NULL; return tempNode; } TreeNode *insertElement(TreeNode *node, ElementType X){ //insert element to Tree if(node==NULL){ return createNode(X); } else{ if(X < node->element){ node->left = insertElement(node->left, X); } else if(X > node->element){ node->right = insertElement(node->right, X); } else if(X == node->element){ printf("Oops! the element is already present in the tree."); } } } TreeNode *displayTree(TreeNode *node){ //display the full tree if(node==NULL){ return; } displayTree(node->left); printf("| %d ", node->element); displayTree(node->right); } main(){ //pointer to root of tree #2 TreeNode *TreePtr; TreeNode *TreeRoot; TreeNode *TreeChild; //Create the root of tree TreePtr = createTree(); TreeRoot = TreePtr; TreeRoot->element = 32; printf("%d\n",TreeRoot->element); insertElement(TreeRoot, 8); TreeChild = TreeRoot->left; printf("%d\n",TreeChild->element); insertElement(TreeRoot, 2); insertElement(TreeRoot, 7); insertElement(TreeRoot, 42); insertElement(TreeRoot, 28); insertElement(TreeRoot, 1); insertElement(TreeRoot, 4); insertElement(TreeRoot, 5); // the output is not as expected :( displayTree(TreeRoot); }

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• Algorithm to Render a Horizontal Binary-ish Tree in Text/ASCII form

  - by Justin L.

  It's a pretty normal binary tree, except for the fact that one of the nodes may be empty. I'd like to find a way to output it in a horizontal way (that is, the root node is on the left and expands to the right). I've had some experience expanding trees vertically (root node at the top, expanding downwards), but I'm not sure where to start, in this case. Preferably, it would follow these couple of rules: If a node has only one child, it can be skipped as redundant (an "end node", with no children, is always displayed) All nodes of the same depth must be aligned vertically; all nodes must be to the right of all less-deep nodes and to the left of all deeper nodes. Nodes have a string representation which includes their depth. Each "end node" has its own unique line; that is, the number of lines is the number of end nodes in the tree, and when an end node is on a line, there may be nothing else on that line after that end node. As a consequence of the last rule, the root node should be in either the top left or the bottom left corner; top left is preferred. For example, this is a valid tree, with six end nodes (node is represented by a name, and its depth): [a0]------------[b3]------[c5]------[d8] \ \ \----------[e9] \ \----[f5] \--[g1]--------[h4]------[i6] \ \--------------------[j10] \-[k3] Which represents the horizontal, explicit binary tree: 0 a / \ 1 g * / \ \ 2 * * * / \ \ 3 k * b / / \ 4 h * * / \ \ \ 5 * * f c / \ / \ 6 * i * * / / \ 7 * * * / / \ 8 * * d / / 9 * e / 10 j (branches folded for compactness; * representing redundant, one-child nodes; note that *'s are actual nodes, storing one child each, just with names omitted here for presentation sake) (also, to clarify, I'd like to generate the first, horizontal tree; not this vertical tree) I say language-agnostic because I'm just looking for an algorithm; I say ruby because I'm eventually going to have to implement it in ruby anyway. Assume that each Node data structure stores only its id, a left node, and a right node. A master Tree class keeps tracks of all nodes and has adequate algorithms to find: A node's nth ancestor A node's nth descendant The generation of a node The lowest common ancestor of two given nodes Anyone have any ideas of where I could start? Should I go for the recursive approach? Iterative?

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• With ' N ' no of nodes, how many different Binary and Binary Search Trees possible ?

  - by siva

  For Binary tree: You no need to consider tree node values, I am interested about different tree topologies with 'N' nodes. For Binary Search Tree: We obviously consider tree node values.

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• CSS issue with elements spanning columns

  - by bigFoot

  Hi folks. Overview: I'm trying to create a relatively simple page layout detailed below and running into problems no matter how I try to approach it. Concept: - A standard-size-block layout. I'll quote unit widths: each content block is 240px square with 5px of margin around it. - A left column of fixed width of 1 unit (245px - 1 block + margin to left). No problems here. - A right column of variable width to fill the remaining space. No problems here either. - In the left column, a number of 1unit x 1unit blocks fixed down the column. Also some blank space at the top - again, not a problem. - In the right column: a number of free-floating blocks of standard unit-sizes which float around and fill the space given to them by the browser window. No problems here. - Lastly, a single element, 2 units wide, which sits half in the left column and half in the right column, and which the blocks in the right column still float around. Here be dragons. Please see here for a diagram: http://is.gd/bPUGI Problem: No matter how I approach this, it goes wrong. Below is code for my existing attempt at a solution. My current problem is that the 1x1 blocks on the right do not respect the 2x1 block, and as a result half of the 2x1 block is overwritten by a 1x1 block in the right-hand column. I'm aware that this is almost certainly an issue with position: absolute taking things out of flow. However, can't really find a way round that which doesn't just throw up another problem instead. Code: <html> <head> <title>wat</title> <style type="text/css"> body { background: #ccc; color: #000; padding: 0px 5px 5px 0px; margin: 0px; } #leftcol { width: 245px; margin-top: 490px; position: absolute; } #rightcol { left: 245px; position: absolute; } #bigblock { float: left; position: relative; margin-top: -240px; background: red; } .cblock { margin: 5px 0px 0px 5px; float: left; overflow: hidden; display: block; background: #fff; } .w1 { width: 240px; } .w2 { width: 485px; } .l1 { height: 240px; } </head> <body> <div class="cblock w2 l1" id="bigblock"> <h1>DRAGONS</h1> <p>Here be they</p> </div> <div id="leftcol"> <div class="cblock w1 l1"> <h1>Left 1</h1> <p>1x1 block</p> </div> </div> <div id="rightcol"> <div class="cblock w1 l1"> <h1>Right 1</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 2</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 3</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 4</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 5</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 6</h1> <p>1x1 block</p> </div> <div class="cblock w1 l1"> <h1>Right 7</h1> <p>1x1 block</p> </div> </div> </body> </html> Constraints: One final note that I need cross-browser compatibility, though I'm more than happy to enforce this with JS if necessary. That said, if a CSS-only solution exists, I'd be extremely happy. Thanks in advance!

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• PHP class constant string variable spanning over multiple lines

  - by ebae

  I want to have a string variable for a PHP class, which would be available to all methods. However, this variable is quite long, so I want to separate it into multiple lines. For example, $variable = "line 1" . "line 2" . "line 3"; But above doesn't work. I tried EOD, but EOD is not allowed within class. And when I declare it outside the class, I can't access the variable from within the class. What is the best way?

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• PHP AJAX mysql event calendar - UI for events spanning multiple days

  - by play

  I have built a PHP calendar system and have pretty much everything done but not sure how to deal with a UI issue involving how the events that stretched out over a couple of days. I want to be able to stretch an event that stretches over couple of days in a div that spans those days in the calendar. Basically I would like to know how to achieve what these guys have achieved with the event that stretches out from 21st to 22nd with the yellow div background. I have been trying to see how I can do it with PHP but I feel like I might be trying the wrong thing. Perhaps this is done with javascript?

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• svn working copy spanning 2 physical drives?

  - by ronenosity

  I have a large repository hosted on dreamhost that I backup daily on a remote machine using a windows scheduled task which updates the working copy located on an external USB 300GB drive connected to the remote machine. The 300GB drive is nearly full with only 26GB of free space remaining. Recently I added a second USB external 1TB drive to increase storage capacity. I would like to ask: what is the best way to use the new 1TB drive? Is it possible to span the working copy across both drives (ex: somehow create a 1.3 TB drive)? If I copied the working copy from the 300GB to the 1TB would svn continue form do I need to retarget the update working copy script to the new 1TB drive and start downloading everything again (least desired option) thanks

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• How to map a Dictionary<string, string> spanning several tables

  - by Kim Johansson

  I have four tables: CREATE TABLE [Languages] ( [Id] INTEGER IDENTITY(1,1) NOT NULL, [Code] NVARCHAR(10) NOT NULL, PRIMARY KEY ([Id]), UNIQUE INDEX ([Code]) ); CREATE TABLE [Words] ( [Id] INTEGER IDENTITY(1,1) NOT NULL, PRIMARY KEY ([Id]) ); CREATE TABLE [WordTranslations] ( [Id] INTEGER IDENTITY(1,1) NOT NULL, [Value] NVARCHAR(100) NOT NULL, [Word] INTEGER NOT NULL, [Language] INTEGER NOT NULL, PRIMARY KEY ([Id]), FOREIGN KEY ([Word]) REFERENCES [Words] ([Id]), FOREIGN KEY ([Language]) REFERENCES [Languages] ([Id]) ); CREATE TABLE [Categories] ( [Id] INTEGER IDENTITY(1,1) NOT NULL, [Word] INTEGER NOT NULL, PRIMARY KEY ([Id]), FOREIGN KEY ([Word]) REFERENCES [Words] ([Id]) ); So you get the name of a Category via the Word - WordTranslation - Language relations. Like this: SELECT TOP 1 wt.Value FROM [Categories] AS c LEFT JOIN [WordTranslations] AS wt ON c.Word = wt.Word WHERE wt.Language = ( SELECT TOP 1 l.Id FROM [Languages] WHERE l.[Code] = N'en-US' ) AND c.Id = 1; That would return the en-US translation of the Category with Id = 1. My question is how to map this using the following class: public class Category { public virtual int Id { get; set; } public virtual IDictionary<string, string> Translations { get; set; } } Getting the same as the SQL query above would be: Category category = session.Get<Category>(1); string name = category.Translations["en-US"]; And "name" would now contain the Category's name in en-US. Category is mapped against the Categories table. How would you do this and is it even possible?

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• IE Print CSS and spanning page breaks

  - by DA

  I've been working on trying to fix an issue with print CSS and IE where things would disappear when printing in landscape mode. It appears the issue is that the element I'm trying to print (a large DIV with content inside it) spans two pages when put into landscape mode. What is happening is when the element spans two pages, the first page is blank, and the second page is printing what would normally be left over from the first page. I think it's related to contained floats: wrapper div floated div1 floated div2 If I set the two nested divs to float: none in the print CSS file, then IE will print them, albeit not in the layout we'd like. Before I spend another hour on this, anyone know what, specifically, is the issue here and if there's a known workaround?

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• Django: query spanning multiple many-to-many relationships

  - by Brant

  I've got some models set up like this: class AppGroup(models.Model): users = models.ManyToManyField(User) class Notification(models.Model): groups_to_notify = models.ManyToManyField(AppGroup) The User objects come from django's authentication system. Now, I am trying to get all the notifications pertaining to the groups that the current user is a part of. I have tried.. notifications = Notification.objects.filter(groups_to_notify=AppGroup.objects.filter(users=request.user)) But that gives an error: more than one row returned by a subquery used as an expression Which I suppose is because the groups_to_notify is checking against several groups. How can I grab all the notifications meant for the user based on the groups he is a part of?

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• CSS Border spanning across another div

  - by Tux

  The problem is that the border of div#content also appears in div#navigation? <html> <head> <title>WUI</title> <style type="text/css"> div#header { } div#navigation { float: left; padding-right: 20pt; } div#content { border: 5px groove; } </style> </head> <body> <div id="header"> <h1>WUI</h1> </div> <br /> <div id="navigation"> <ul> <li>Home</li> <li>Login</li> </ul> </div> <div id="content"> <p>I like when you ride with that booty on me!</p> </div> </body> </html> EDIT: I want the left side (navigation) to appear as a sidebar to the left and the content after that (to the right). I'm applying the border to the content but that border also appears in div of navigation. I hope it is clear now.

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• Spanning columns in HTML table.

  - by Tony

  I'm trying do to a very simple operation of merging two columns in a table. This seems easy with the colspan, but if I merge different columns without leaving at least one row without any merged columns, the sizing gets completely messed up. Please see the following example at http://www.allthingsdope.com/table.html or take a look at and try the following code: Good: <table width="700px"> <tr> <th width="100px">1: 100px</th> <td width="300px">2: 300px</td> <td width="200px">3: 200px</td> <td width="100px">4: 100px</td> </tr> <tr> <th width="100px">1: 100px</th> <td colspan=2 width="500px" >2 & 3: 500px</td> <td width="100px">4: 100px</td> </tr> <tr> <th width="100px">1: 100px</th> <td width="300px">2: 300px</td> <td colspan=2 width="300px">3 & 4: 300px</td> </tr> </table> Bad: <table width="700px"> <tr> <th width="100px">1: 100px</th> <td colspan=2 width="500px" >2 & 3: 500px</td> <td width="100px">4: 100px</td> </tr> <tr> <th width="100px">1: 100px</th> <td width="300px">2: 300px</td> <td colspan=2 width="300px">3 & 4: 300px</td> </tr> </table> This seems so simple but I can not figure it out!

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• SQL: find entries in 1:n relation that don't comply with condition spanning multiple rows

  - by milianw

  I'm trying to optimize SQL queries in Akonadi and came across the following problem that is apparently not easy to solve with SQL, at least for me: Assume the following table structure (should work in SQLite, PostgreSQL, MySQL): CREATE TABLE a ( a_id INT PRIMARY KEY ); INSERT INTO a (a_id) VALUES (1), (2), (3), (4); CREATE TABLE b ( b_id INT PRIMARY KEY, a_id INT, name VARCHAR(255) NOT NULL ); INSERT INTO b (b_id, a_id, name) VALUES (1, 1, 'foo'), (2, 1, 'bar'), (3, 1, 'asdf'), (4, 2, 'foo'), (5, 2, 'bar'), (6, 3, 'foo'); Now my problem is to find entries in a that are missing name entries in table b. E.g. I need to make sure each entry in a has at least the name entries "foo" and "bar" in table b. Hence the query should return something similar to: a_id = 3 is missing name "bar" a_id = 4 is missing name "foo" and "bar" Since both tables are potentially huge in Akonadi, performance is of utmost importance. One solution in MySQL would be: SELECT a.a_id, CONCAT('|', GROUP_CONCAT(name ORDER BY NAME ASC SEPARATOR '|'), '|') as names FROM a LEFT JOIN b USING( a_id ) GROUP BY a.a_id HAVING names IS NULL OR names NOT LIKE '%|bar|foo|%'; I have yet to measure the performance tomorrow, but severly doubt it's any fast for tens of thousand of entries in a and thrice as many in b. Furthermore we want to support SQLite and PostgreSQL where to my knowledge the GROUP_CONCAT function is not available. Thanks, good night.

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