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• Merge Primary Keys - Cascade Update

  - by Chris Jackson

  Is there a way to merge two primary keys into one and then cascade update all affected relationships? Here's the scenario: Customers (idCustomer int PK, Company varchar(50), etc) CustomerContacts (idCustomerContact int PK, idCustomer int FK, Name varchar(50), etc) CustomerNotes (idCustomerNote int PK, idCustomer int FK, Note Text, etc) Sometimes customers need to be merged into one. For example, you have a customer with the id of 1 and another with the id of 2. You want to merge both, so that everything that was 2 is now 1. I know I could write a script that updates all affected tables one by one, but I'd like to make it more future proof by using the cascade rules, so I don't have to update the script every time there is a new relationship added. Any ideas?

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• How to insert an n:m-relationship with technical primary keys generated by a sequence?

  - by bitschnau

  Let's say I have two tables with several fields and in every table there is a primary key which is a technical id generated by a database sequence: table1 table2 ------------- ------------- field11 <pk> field21 <pk> field12 field22 field11 and field21 are generated by sequences. Also there is a n:m-relationship between table1 und table2, designed in table3: table3 ------------- field11 <fk> field21 <fk> The ids in table1 und table2 are generated during the insert statement: INSERT INTO table1 VALUES (table1_seq1.NEXTVAL, ... INSERT INTO table2 VALUES (table2_seq1.NEXTVAL, ... Therefore I don't know the primary key of the added row in the data-access-layer of my program, because the generation of the pk happens completely in the database. What's the best practice to update table3 now? How can I gain access to the primary key of the rows I just inserted?

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• How To Query Many-to-Many Table (one table's values becomes column headers)

  - by CRice

  Given this table structure, I want to flatten out the many-to-many relationships and make the values in the Name field of one table into column headers and the quantities from the same table into column values. The current idea which will work is to put the values into a Dictionary (hashtable) and represent this data in code but im wondering if there is a SQL way to do this. I am also using Linq-to-SQL for data access so a Linq-to-SQL solution would be ideal. [TableA] (int Id) [TableB] (int id, string Name) [TableAB] (int tableAId, int tableBId, int Quantity) fk: TableA.Id joins to TableAB.tableAId fk: TableB.Id joins to TableAB.tableBId Is there a way I can query the three tables and return one result for example: TableA [Id] 1 TableB [Id], [Name] 1, "Red" 2, "Green" 3, "Blue" TableAB [TableAId], [TableBId], [Quantity] 1 1 5 1 2 6 1 3 7 Query Result: [TableA.Id], [Red], [Green], [Blue] 1, 5, 6, 7

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• group_concat on an empty join in MySQL

  - by Yossarian

  Hello, I've got the following problem: I have two tables: (simplified) +--------+ +-----------+ | User | | Role | +--------+ +-----------+ | ID<PK> | | ID <PK> | +--------+ | Name | +-----------+ and M:N relationship between them +-------------+ | User_Role | +-------------+ | User<FK> | | Role<FK> | +-------------+ I need to create a view, which selects me: User, and in one column, all of his Roles (this is done by group_concat). I've tried following: SELECT u.*, group_concat(r.Name separator ',') as Roles FROM User u LEFT JOIN User_Role ur ON ur.User=u.ID LEFT JOIN Role r ON ur.Role=r.ID GROUP BY u.ID; However, this works for an user with some defined roles. Users without role aren't returned. How can I modify the statement, to return me User with empty string in Roles column when User doesn't have any Role? Explanation: I'm passing the SQL data directly to a grid, which then formats itself, and it is easier for me to create slow and complicated view, than to format it in my code. I'm using MySQL

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• Foreign Key vs. Independent Relationships - is there improvement with Entity Framework 5?

  - by zam6ak

  I have read several articles and questions on concept of foreign key vs independent relationship when using Entity Framework. And I am still not 100% sure which way to go.... I would prefer not to "pollute" my domain POCOs by having a property that will be used in FK relationship when I already have a property reference to "has a" object. My questions are (looking at you @EFTeam, @Ladislav Mrnka) are there any improvements on this subject in the upcoming Entity Framework v5? are there more advantages if I use FK instead of independent associations (particularly with code first)?

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• Missing something with Entity Framework for .NET 3.5?

  - by AC

  Is it not possible to have EF create the necessary entities when I have two related tables linked with a FK in .NET3.5SP1? I see where the checkbox to support this is disabled but it is available in .NET4. I've got a DB that has only tables with relationships in it. I need to build a Silverlight app (SL4) that allows management of the data within this app. I can't use .NET4 on the server... only .NET3.5SP1 so FK relationship bit in EF4 isn't available to me. Looking to avoid building as much of the plumbing to get back to the DB from the SL4 app as possible...

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• how do i release the auto increment serial nos that are missing

  - by mmdel

  i have a table with auto increment field and i am using transactions when inserting new data. now i find there are a few serial nos that are missing. suppose the last serial no was 475, now when i insert new row, the serial allotted to it is 481. how do i correct this. table_A fields ID(Auto increment),Name,Address table_B fields ID(Auto increment FK TO table_A ID),Tel,Fax,Email,Salesman table_C fields ID(Auto increment FK TO table_A ID),monthly_commitment mysql_query(BEGIN); $a = mysql_query("INSERT INTO table_A VALUES('','name','address')"); $b = mysql_query("INSERT INTO table_B VALUES('','tel','fax','email','salesman')"); $b = mysql_query("INSERT INTO table_C VALUES('','monthly commitment')"); if(($a) && ($b) && ($c)){mysql_query("COMMIT");} else {mysql_query("ROLLBACK");}

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• Set to null a parent record so that children are removed: howto?

  - by EugeneP

  How to delete a child row (on delete cascade ?) when setting a null value on a parent? Here's the db design. table A [id, b_id_1, b_id_2] table B [id, other fields...] b_id_1 and b_id_2 can be NULL if any of them is null, it means NO B records for corresponding FK (there are 2 of them) so (b_id_1,b_id_2) can be (null,null), (100, null), (null, 100_or_any_other_number) etc How in one SQL query both set b_id_1 or b_id_2 to null and delete all rows from B that have this id? What FK design should be applied to the 2 tables? what foreign keys should be added? A - B (FK_1: A.b_id_1 references B.id, FK_2: A.b_id_2 references B.id) and also B-A (FK_3: B.id references A.b_id_1, FK_4: B.id references A.b_id_2) ? But again, setting an A's b_id_1 or A's b_id_2 to null - will it remove any of B's records? I don't think so. So how to do that?

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• using dummy row with NOT NULL to solve DEFAUT NULL

  - by Tony38

  I know having DEFAULT NULLS is not a good practice but I have many optional lookup values which are FK in the system so to solve this issue here is what i am doing: I use NOT NULL for every FK / lookup valve field. I have the first row in every table which is PK id = 1 as a dummy row with just "none" in all the columns. this way I can use NOT NULL in my schema and if needed reference to the none row values which should be null. Is this a good design or any other work arounds?

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• FKs on all tables for status colunm

  - by Jonarch

  I have a colunm "Status" in every table in my DB. The purpose of it is to show if the given row is in use or if it has been deactivated. So values can be (0=deactive and 1= active). Two ways I see this: I can have enums or I am thinking if it is better to keep this colunm as a FK which references the main system data dictionary table which has all the codes used on the system. (website) The benefit is every table, every row can then be centralized through this FK. So if i ever want to check all rows which are deactive on my system i can from this table as all th child tables will have like status = ID 233, where 233 = deactive in the data dictionary table. Any benefit or should i stick with the old way of enums?. Also I am thinking if i need one more status for deleted or is that same as deactivated?

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• JPA Bidirectional OneToMany and ManyToOne?

  - by PhoenixJon

  I'm using Oracle JDeveloper 11g Release 2. I created two tables A and B using SQL developer. Table A has a FK to table B. Using the Entities from Tables function, I created two JPA files from it. A has @ManyToOne annotation on FK. And also B has @OneToMany annotation to A. I don't want this. Can I remove this @OneToMany annotation automatically? public class A implements Serializable { ... @ManyToOne @JoinColumn(name = "FIELD_B") private B b; ... } public class B implements Serializable { ... @OneToMany(mappedBy = "B") private List<A> assetList; ... } I don't need @OneToMany mapping.

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• LINQ to Entites: Doing a count over one-to-many relationships

  - by chris

  I have a couple of tables where there are one to many relationships. Let's say I have a Country table, a State table with a FK to Country, and a City table with a FK to State. I'd like to be able to create a count of all Cities for a given country, and also a count of cities based on a filter - something like: foreach( var country in Model.Country ) { total = country.State.All().City.All().Count() ; filtered = country.State.All().City.Any(c=>c.field == value).Count(); } Obviously, this doesn't work - is there any way to do this?

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• How to avoid Foreign Keys constraints for all tables in DB truncate ?

  - by eugeneK

  Hi, for designing purposes i need to truncate all DB which has lots of FK's. I cannot use DELETE command simply because some tables set with Identity of TinyInts and contain about 150 items. this is a query ( truncate all tables in selected DB ) i'm trying to run Declare @t varchar (1024) Declare tbl_cur cursor for select TABLE_NAME from INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE' OPEN tbl_cur FETCH NEXT from tbl_cur INTO @t WHILE @@FETCH_STATUS = 0 BEGIN EXEC ('TRUNCATE TABLE '+ @t) FETCH NEXT from tbl_cur INTO @t END CLOSE tbl_cur DEALLOCATE tbl_Cur What the best and easiest way to achieve truncate on DB with many FK's ?

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• Symfony models with foreign keys

  - by Daniel Hertz

  So I have 2 models. Users and Groups. Each group has a user as the creator and a group has many users. The FK of these tables are set up correctly, but I was wondering if there was an easier way to get all related FK objects from other objects. For example, with a group object, is there a built in method to get the user object of the creator? Or for a user, is there a built in method to get all group object that he belongs to? I couldn't find out how to do this with the documentation on the symfony page. From what I see I feel like I need to create methods and use doctrine to access the appropriate tables using the current objects id and so on. Thanks!

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• What arguments do I send a function being called by a button in python?

  - by Jared

  I have a UI, in that UI is 4 text fields and 1 int field, then I have a function that calls to another function based on what's inside of the text fields, this function has (self, *args). My function that is being called to takes five arguments and I don't know what to put in it to make it actually work with my UI because python button's send an argument of their own. I have tried self and *args, but it doesn't work. Here is my code, didn't include most of the UI code since it is self explanatory: def crBC(self, IKJoint, FKJoint, bindJoint, xQuan, switch): ''' You should have a controller with an attribute 'ikFkBlend' - The name can be changed after the script executes. Controller should contain an enum - FK/DYN(0), IK(1). Specify the IK joint, then either the dynamic or FK joint, then the bind joint. Then a quantity of joints to pass through and connect. Tested currently on 600 joints (200 x 3), executed in less than a second. Returns nothing. Please open your script editor for details. ''' import itertools # gets children joints of the selected joint chHipIK = cmds.listRelatives(IKJoint, ad = True, type = 'joint') chHipFK = cmds.listRelatives(FKJoint, ad = True, type = 'joint') chHipBind = cmds.listRelatives(bindJoint, ad = True, type = 'joint') # list is built backwards, this reverses the list chHipIK.reverse() chHipFK.reverse() chHipBind.reverse() # appends the initial joint to the list chHipIK.append(IKJoint) chHipFK.append(FKJoint) chHipBind.append(bindJoint) # puts the last joint at the start of the list because the initial joint # was added to the end chHipIK.insert(0, chHipIK.pop()) chHipFK.insert(0, chHipFK.pop()) chHipBind.insert(0, chHipBind.pop()) # pops off the remaining joints in the list the user does not wish to be blended chHipBind[xQuan:] = [] chHipIK[xQuan:] = [] chHipFK[xQuan:] = [] # goes through the bind joints, makes a blend colors for each one, connects # the switch to the blender for a, b, c in itertools.izip(chHipBind, chHipIK, chHipFK): rotBC = cmds.shadingNode('blendColors', asUtility = True, n = a + 'rotate_BC') tranBC = cmds.shadingNode('blendColors', asUtility = True, n = a + 'tran_BC') scaleBC = cmds.shadingNode('blendColors', asUtility = True, n = a + 'scale_BC') cmds.connectAttr(switch + '.ikFkSwitch', rotBC + '.blender') cmds.connectAttr(switch + '.ikFkSwitch', tranBC + '.blender') cmds.connectAttr(switch + '.ikFkSwitch', scaleBC + '.blender') # goes through the ik joints, connects to the blend colors cmds.connectAttr(b + '.rotate', rotBC + '.color1', force = True) cmds.connectAttr(b + '.translate', tranBC + '.color1', force = True) cmds.connectAttr(b + '.scale', scaleBC + '.color1', force = True) # connects FK joints to the blend colors cmds.connectAttr(c + '.rotate', rotBC + '.color2') cmds.connectAttr(c + '.translate', tranBC + '.color2') cmds.connectAttr(c + '.scale', scaleBC + '.color2') # connects blend colors to bind joints cmds.connectAttr(rotBC + '.output', a + '.rotate') cmds.connectAttr(tranBC + '.output', a + '.translate') cmds.connectAttr(scaleBC + '.output', a + '.scale') ------------------- def execCrBC(self, *args): g.crBC(cmds.textField(self.ikJBC, q = True, tx = True), cmds.textField(self.fkJBC, q = True, tx = True), cmds.textField(self.bindJBC, q = True, tx = True), cmds.intField(self.bQBC, q = True, v = True), cmds.textField(self.sCBC, q = True, tx = True)) ------------------- self.bQBC = cmds.intField() cmds.text(l = '') self.sCBC = cmds.textField() cmds.text(l = '') cmds.button(l = 'Help Docs', c = self.crBC.__doc__) cmds.setParent('..') cmds.button(l = 'Create', c = self.execCrBC) Here is the code causing the problem as requested: import maya.cmds as cmds import jtRigUI.createDummyRig as dum import jtRigUI.createSkeleton as sk import jtRigUI.generalUtilities as gu import jtRigUI.createLegRig as lr import jtRigUI.createArmRig as ar class RUI(dum.Dict, dum.Dummy, sk.Skel, sk.FiSkel, lr.LeanLocs, lr.LegRig, ar.ArmRig, gu.Gutils): def __init__(self, charNameUI, gScaleUI, fingButtonGrp, thumbCheckBox, spineButtonGrp, neckButtonGrp, ikJBC, fkJBC, bindJBC, bQBC, sCBC): rigUI = 'rigUI' if cmds.window(rigUI, exists = True): cmds.deleteUI(rigUI) rigUI = cmds.window(rigUI, t = 'JT Rigging UI', sizeable = False, tb = True, mnb = False, mxb = False, menuBar = True, tlb = True, nm = 5) form = cmds.formLayout() tabs = cmds.tabLayout(innerMarginWidth = 1, innerMarginHeight = 1) rigUIMenu = cmds.menu('Help', hm = True) aboutMenu = cmds.menuItem('about') cmds.popupMenu('about', button = 1) deleteUIMenu = cmds.menu('Delete', hm = True) cmds.menuItem('dummySkeleton') cmds.formLayout(form, edit = True, attachForm = ((tabs, 'top', 0), (tabs, 'left', 0), (tabs, 'bottom', 0), (tabs, 'right', 0)), w = 30) tab1 = cmds.rowColumnLayout('Dummy') #cmds.columnLayout(rowSpacing = 10) #cmds.setParent('..') cmds.frameLayout(l = 'A: Dummy Skeleton Setup', w = 400) self.charNameUI = cmds.textFieldGrp (label="Optional Character Name:", ann="Insert a name for the character or leave empty.", tx = '', w = 1) fingJUI = cmds.frameLayout(l = 'B: Number of Fingers', w = 10) cmds.text('\n', h = 5) self.fingButtonGrp = cmds.radioButtonGrp('fingRadio', p = fingJUI, l = 'Fingers: ', sl = 4, w = 1, numberOfRadioButtons = 4, labelArray4 = ['One', 'Two', 'Three', 'Four'], ct2 = ('left', 'left'), cw5 = [60,60,60,60,60]) self.thumbCheckBox = cmds.checkBoxGrp(l = 'Thumb: ', v1 = True) cmds.text('\n', h = 5) spineJUI = cmds.frameLayout(l = 'C: Number of Spine Joints') cmds.text('\n', h = 5) self.spineButtonGrp = cmds.radioButtonGrp('spineRadio', p = spineJUI, l = 'Spine Joints: ', sl = 2, w = 1, numberOfRadioButtons = 3, labelArray3 = ['Three', 'Five', 'Ten'], ct2 = ('left', 'left'), cw4 = [95,95,95,95]) cmds.text('\n', h = 5) neckJUI = cmds.frameLayout(l = 'D: Number of Neck Joints') cmds.text('\n', h = 5) self.neckButtonGrp = cmds.radioButtonGrp('neckRadio', p = neckJUI, l = 'Neck Joints: ', sl = 0, w = 1, numberOfRadioButtons = 3, labelArray3 = ['Two', 'Three', 'Four'], ct2 = ('left', 'left'), cw4 = [95,95,95,95]) cmds.text('\n', h = 5) cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') cmds.frameLayout('E: Creation') cmds.text('SAVE FIRST: CAN NOT UNDO', bgc = (0.2,0.2,0.2)) cmds.button(l = '\nCreate Dummy Skeleton\n', c = self.build) # also have it make char name field grey cmds.text('Elbows and Knees must have bend.', bgc = (0.2,0.2,0.2)) cmds.columnLayout() cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') tab2 = cmds.rowColumnLayout('Skeleton') cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'A: Skeleton Setup') cmds.text('SAVE FIRST: CAN NOT UNDO', bgc = (0.2,0.2,0.2)) cmds.button(l = '\nConvert to Skeleton - Orient - Set LRA\n', c = self.buildSkel) self.gScaleUI = cmds.textFieldGrp (label="Scale Multiplier:", ann="Scale multipler of Character: basis for all further base controllers", tx = '1.0', w = 1, ed = False, en = False, visible = True) cmds.frameLayout('B: Manual Orientation') cmds.text('You must manually check finger, thumb, leg, foot orientation specifically.\nConfirm rest of joints.\nSpine: X aim, Y point backwards from spine, Z to the side.\nFingers: X is aim, Y points upwards, Z to the side - Spread on Y, curl on Z.\nFoot: Pivots on Y, rolls on Z, leans on X.') cmds.columnLayout() cmds.setParent('..') cmds.frameLayout('C: Finalize Creation of Skeleton') cmds.button(l = '\nFinalize Skeleton\n', c = self.finishS) cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') tab3 = cmds.rowColumnLayout('Legs') cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'A: Leg Rig Setup') cmds.button(l = '\nGenerate Foot Lean Locators\n', c = self.makeLean) cmds.text('Place on either side of the foot.\nDo not rotate: Automatic orientation in place.') cmds.frameLayout(l = 'B: Rig Legs') cmds.button(l = '\nRig Legs\n', c = self.makeLegs) cmds.setParent('..') cmds.setParent('..') cmds.setParent('..') tab4 = cmds.rowColumnLayout('Arms') cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'A: Arm Rig Setup') cmds.button(l = '\nA: Rig Arms\n', c = self.makeArms) cmds.setParent('..') cmds.setParent('..') tab5 = cmds.rowColumnLayout('Spine and Head') cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'Spine Rig Setup') cmds.setParent('..') cmds.setParent('..') tab6 = cmds.rowColumnLayout('Stretchy IK') cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'Stretchy Setup') cmds.setParent('..') cmds.setParent('..') tab6 = cmds.rowColumnLayout('Extras') cmds.scrollLayout(saw = 600, sah = 600, cr = True) cmds.columnLayout(columnAttach = ('both', 5), rowSpacing = 10, columnWidth = 150) cmds.setParent('..') cmds.frameLayout(l = 'General Utitlities') cmds.text('\nHere are all my general utilities for various things') cmds.frameLayout(l = 'Automatic Blend Colors Creation and Connection') cmds.rowColumnLayout(nc = 5, w = 10) cmds.text('IK Joint:') cmds.text(l = '') cmds.text('FK/Dyn Joint:') cmds.text(l = '') cmds.text('Bind Joint:') self.ikJBC = cmds.textField() cmds.text(l = '') self.fkJBC = cmds.textField() cmds.text(l = '') self.bindJBC = cmds.textField() cmds.text(' \nBlend Quantity:') cmds.text(l = '') cmds.text(' \nSwitch Control:') cmds.text(l = '') cmds.text(l = '') self.bQBC = cmds.intField() cmds.text(l = '') self.sCBC = cmds.textField() cmds.text(l = '') cmds.button(l = 'Help Docs', c = self.crBC.__doc__) cmds.setParent('..') cmds.button(l = 'Create', c = self.execCrBC) cmds.text(l = '') cmds.setParent('..') cmds.frameLayout(l = 'Make Spline IK Curve Stretch And Squash') cmds.rowColumnLayout(nc = 5, w = 10) cmds.text('Curve Name:') cmds.text(l = '') cmds.text('Setup Name:') cmds.text(l = '') cmds.text('Joint Quantity:') self.ikJBC = cmds.textField() cmds.text(l = '') self.fkJBC = cmds.textField() cmds.text(l = '') self.bindJBC = cmds.textField() cmds.text(' \nSwitch Control:') cmds.text(l = '') cmds.text(' \nGlobal Control:') cmds.text(l = '') cmds.text(l = '') self.bQBC = cmds.intField() cmds.text(l = '') self.sCBC = cmds.textField() cmds.text(l = '') cmds.button(l = 'Help Docs', c = self.crBC.__doc__) cmds.setParent('..') cmds.button(l = 'Create', c = self.execCrBC) cmds.setParent('..') cmds.showWindow(rigUI) r = RUI('charNameUI', 'gScaleUI', 'fingButtonGrp', 'thumbCheckBox', 'spineButtonGrp', 'neckButtonGrp', 'ikJBC', 'fkJBC', 'bindJBC', 'bQBC', 'sCBC') # last modified at 6.20 pm 29th June 2011

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• When row estimation goes wrong

  - by Dave Ballantyne

  Whilst working at a client site, I hit upon one of those issues that you are not sure if that this is something entirely new or a bug or a gap in your knowledge. The client had a large query that needed optimizing.  The query itself looked pretty good, no udfs, UNION ALL were used rather than UNION, most of the predicates were sargable other than one or two minor ones.  There were a few extra joins that could be eradicated and having fixed up the query I then started to dive into the plan. I could see all manor of spills in the hash joins and the sort operations,  these are caused when SQL Server has not reserved enough memory and has to write to tempdb.  A VERY expensive operation that is generally avoidable.  These, however, are a symptom of a bad row estimation somewhere else, and when that bad estimation is combined with other estimation errors, chaos can ensue. Working my way back down the plan, I found the cause, and the more I thought about it the more i came convinced that the optimizer could be making a much more intelligent choice. First step is to reproduce and I was able to simplify the query down a single join between two tables, Product and ProductStatus,  from a business point of view, quite fundamental, find the status of particular products to show if ‘active’ ,’inactive’ or whatever. The query itself couldn’t be any simpler The estimated plan looked like this: Ignore the “!” warning which is a missing index, but notice that Products has 27,984 rows and the join outputs 14,000. The actual plan shows how bad that estimation of 14,000 is : So every row in Products has a corresponding row in ProductStatus.  This is unsurprising, in fact it is guaranteed,  there is a trusted FK relationship between the two columns.  There is no way that the actual output of the join can be different from the input. The optimizer is already partly aware of the foreign key meta data, and that can be seen in the simplifiction stage. If we drop the Description column from the query: the join to ProductStatus is optimized out. It serves no purpose to the query, there is no data required from the table and the optimizer knows that the FK will guarantee that a matching row will exist so it has been removed. Surely the same should be applied to the row estimations in the initial example, right ?  If you think so, please upvote this connect item. So what are our options in fixing this error ? Simply changing the join to a left join will cause the optimizer to think that we could allow the rows not to exist. or a subselect would also work However, this is a client site, Im not able to change each and every query where this join takes place but there is a more global switch that will fix this error,  TraceFlag 2301. This is described as, perhaps loosely, “Enable advanced decision support optimizations”. We can test this on the original query in isolation by using the “QueryTraceOn” option and lo and behold our estimated plan now has the ‘correct’ estimation. Many thanks goes to Paul White (b|t) for his help and keeping me sane through this

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• ORM model and DAO in my particular case

  - by EugeneP

  I have the DB structure as follows: table STUDENT (say, id, surname, etc) table STUDENT_PROPERTIES (say, name_of_the_property:char, value_of_the_property:char, student_id:FK) table COURSE (id, name, statusofcourse_id) table STATUSOFCOURSE (id, name_of_status:char ('active','inactive','suspended' etc)) table STUDENT_COURSE (student_id,course_id,statusofcourse_id) Let's try to pick up domain objects in my database: Student and Course are main entities. Student has a list of courses he attends, also he has a list of properties, that is all for this student. Next, Course entitity. It may contain a list of students that attend it. But in fact, the whole structure looks like this: the starting point is Student, with it's PK we can look a list of his properties, then we look into the STUDENT_COURSE and extract both FK of the Course entity and also the Status of the combination, it would look like "Student named bla bla, with all his properties, attends math and the status of it is "ACTIVE". now, quotation 1) Each DAO instance is responsible for one primary domain object or entity. If a domain object has an independent lifecycle, it should have its own DAO. 2) The DAO is responsible for creations, reads (by primary key), updates, and deletions -- that is, CRUD -- on the domain object. Now, first question is What are entities in my case? Student, Course, Student_Course, Status = all except for StudentProperties? Do I have to create a separate DAO for every object?

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• How to keep track of a private messaging system using MongoDB?

  - by luckytaxi

  Take facebook's private messaging system where you have to keep track of sender and receiver along w/ the message content. If I were using MySQL I would have multiple tables, but with MongoDB I'll try to avoid all that. I'm trying to come up with a "good" schema that can scale and is easy to maintain. If I were using mysql, I would have a separate table to reference the user and and message. See below ... profiles table user_id first_name last_name message table message_id message_body time_stamp user_message_ref table user_id (FK) message_id (FK) is_sender (boolean) With the schema listed above, I can query for any messages that "Bob" may have regardless if he's the recipient or sender. Now how to turn that into a schema that works with MongoDB. I'm thinking I'll have a separate collection to hold the messages. Problem is, how can I differentiate between the sender and the recipient? If Bob logs in, what do I query against? Depending on whether Bob initiated the email, I don't want to have to query against "sender" and "receiver" just to see if the message belongs to the user.

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• SQL Joining Two or More from Table B with Common Data in Table A

  - by Matthew Frederick

  The real-world situation is a series of events that each have two or more participants (like sports teams, though there can be more than two in an event), only one of which is the host of the event. There is an Event db table for each unique event and a Participant db table with unique participants. They are joined together using a Matchup table. They look like this: Event EventID (PK) (other event data like the date, etc.) Participant ParticipantID (PK) Name Matchup EventID (FK to Event table) ParicipantID (FK to Participant) Host (1 or 0, only 1 host = 1 per EventID) What I'd like to get as a result is something like this: EventID ParticipantID where host = 1 Participant.Name where host = 1 ParticipantID where host = 0 Participant.Name where host = 0 ParticipantID where host = 0 Participant.Name where host = 0 ... Where one event has 2 participants and another has 3 participants, for example, the third participant column data would be null or otherwise noticeable, something like (PID = ParticipantID): EventID PID-1(host) Name-1 (host) PID-2 Name-2 PID-3 Name-3 ------- ----------- ------------- ----- ------ ----- ------ 1 7 Lions 8 Tigers 12 Bears 2 11 Dogs 9 Cats NULL NULL I suspect the answer is reasonably straightforward but for some reason I'm not wrapping my head around it. Alternately it's very difficult. :) I'm using MYSQL 5 if that affects the available SQL.

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• How to Set Customer Table with Multiple Phone Numbers? - Relational Database Design

  - by user311509

  CREATE TABLE Phone ( phoneID - PK . . . ); CREATE TABLE PhoneDetail ( phoneDetailID - PK phoneID - FK points to Phone phoneTypeID ... phoneNumber ... . . . ); CREATE TABLE Customer ( customerID - PK firstName phoneID - Unique FK points to Phone . . . ); A customer can have multiple phone numbers e.g. Cell, Work, etc. phoneID in Customer table is unique and points to PhoneID in Phone table. If customer record is deleted, phoneID in Phone table should also be deleted. Do you have any concerns on my design? Is this designed properly? My problem is phoneID in Customer table is a child and if child record is deleted then i can not delete the parent (Phone) record automatically.

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• Mapping composite foreign keys in a many-many relationship in Entity Framework

  - by Kirk Broadhurst

  I have a Page table and a View table. There is a many-many relationship between these two via a PageView table. Unfortunately all of these tables need to have composite keys (for business reasons). Page has a primary key of (PageCode, Version), View has a primary key of (ViewCode, Version). PageView obviously enough has PageCode, ViewCode, and Version. The FK to Page is (PageCode, Version) and the FK to View is (ViewCode, Version) Makes sense and works, but when I try to map this in Entity framework I get Error 3021: Problem in mapping fragments...: Each of the following columns in table PageView is mapped to multiple conceptual side properties: PageView.Version is mapped to (PageView_Association.View.Version, PageView_Association.Page.Version) So clearly enough, EF is having a complain about the Version column being a common component of the two foreign keys. Obviously I could create a PageVersion and ViewVersion column in the join table, but that kind of defeats the point of the constraint, i.e. the Page and View must have the same Version value. Has anyone encountered this, and is there anything I can do get around it? Thanks!

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• UPDATE query that fixes orphaned records

  - by Jed

  I have an Access database that has two tables that are related by PK/FK. Unfortunately, the database tables have allowed for duplicate/redundant records and has made the database a bit screwy. I am trying to figure out a SQL statement that will fix the problem. To better explain the problem and goal, I have created example tables to use as reference: You'll notice there are two tables, a Student table and a TestScore table where StudentID is the PK/FK. The Student table contains duplicate records for students John, Sally, Tommy, and Suzy. In other words the John's with StudentID's 1 and 5 are the same person, Sally 2 and 6 are the same person, and so on. The TestScore table relates test scores with a student. Ignoring how/why the Student table allowed duplicates, etc - The goal I'm trying to accomplish is to update the TestScore table so that it replaces the StudentID's that have been disabled with the corresponding enabled StudentID. So, all StudentID's = 1 (John) will be updated to 5; all StudentID's = 2 (Sally) will be updated to 6, and so on. Here's the resultant TestScore table that I'm shooting for (Notice there is no longer any reference to the disabled StudentID's 1-4): Can you think of a query (compatible with MS Access's JET Engine) that can accomplish this goal? Or, maybe, you can offer some tips/perspectives that will point me in the right direction. Thanks.

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• Avoiding Duplicate Data in DB (for use with Rails)

  - by ants

  I have five tables that I am trying to get to work nicely together but may need some help. I have three main tables: accounts members and roles. With two join tables account_members and account_member_roles. The accounts and members table are joined by account_members (fk account_id and member_id) table. The other 2 tables are the problem (roles and account_member_roles). A member of an account can have more than one role and I have the account_member_roles (fk account_member_id and role_id) table joining the account_members join table and the roles table. That seems logical but can you have a relationship with a join table? What I'd like to be able to do is when creaeting an account, for instance, I would like @account.save to include the roles and update the account_member_roles table neatly ..... but through the account_members join table. I've tried ..... accept_nested_attributes_for :members, :account_member_roles in the account.rb but I get ..... ActiveRecord::HasManyThroughCantAssociateThroughHasManyReflection (Cannot modify association 'Account#account_member_roles' because the source reflection class 'AccountMemberRole' is associated to 'AccountMember' via :has_many.) upon trying to save a record. Any advice on how I should approach this? CIA -ants

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• Mapping composite foreign keys in a many-many relationship, with overlapping components.

  - by Kirk Broadhurst

  I have a Page table and a View table. There is a many-many relationship between these two via a PageView table. Unfortunately all of these tables need to have composite keys (for business reasons). Page has a primary key of (PageCode, Version), View has a primary key of (ViewCode, Version). PageView obviously enough has PageCode, ViewCode, and Version. The FK to Page is (PageCode, Version) and the FK to View is (ViewCode, Version) Makes sense and works, but when I try to map this in Entity framework I get Error 3021: Problem in mapping fragments...: Each of the following columns in table PageView is mapped to multiple conceptual side properties: PageView.Version is mapped to (PageView_Association.View.Version, PageView_Association.Page.Version) So clearly enough, EF is having a complain about the Version column being a common component of the two foreign keys. Obviously I could create a PageVersion and ViewVersion column in the join table, but that kind of defeats the point of the constraint, i.e. the Page and View must have the same Version value. Has anyone encountered this, and is there anything I can do get around it? Thanks!

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• SQL Design: representing a default value with overrides?

  - by Mark Harrison

  I need a sparse table which contains a set of "override" values for another table. I also need to specify the default value for the items overridden. For example, if the default value is 17, then foo,bar,baz will have the values 17,21,17: table "things" table "xvalue" name stuff name xval ---- ----- ---- ---- foo ... bar 21 bar ... baz ... If I don't care about a FK from xvalue.name - things.name, I could simply put a "DEFAULT" name: table "xvalue" name xval ---- ---- DEFAULT 17 bar 21 But I like having a FK. I could have a separate default table, but it seems odd to have 2x the number of tables. table "xvalue_default" xval ---- 17 table "xvalue" name xval ---- ---- bar 21 I could have a "defaults table" tablename attributename defaultvalue xvalue xval 17 but then I run into type issues on defaultvalue. My operations guys prefer as compact a representation as possible, so they can most easily see the "diff" or deviations from the default. What's the best way to represent this, including the default value? This will be for Oracle 10.2 if that makes a difference.

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