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• Data Modeling Help - Do I add another table, change existing table's usage, or something else?

  - by StackOverflowNewbie

  Assume I have the following tables and relationships: Person - Id (PK) - Name A Person can have 0 or more pets: Pet - Id (PK) - PersonId (FK) - Name A person can have 0 or more attributes (e.g. age, height, weight): PersonAttribute _ Id (PK) - PersonId (FK) - Name - Value PROBLEM: I need to represent pet attributes, too. As it turns out, these pet attributes are, in most cases, identical to the attributes of a person (e.g. a pet can have an age, height, and weight too). How do I represent pet attributes? Do I create a PetAttribute table? PetAttribute Id (PK) PetId (FK) Name Value Do I change PersonAttribute to GenericAttribute and have 2 foreign keys in it - one connecting to Person, the other connecting to Pet? GenericAttribute Id (PK) PersonId (FK) PetId (FK) Name Value NOTE: if PersonId is set, then PetId is not set. If PetId is set, PersonId is not set. Do something else?

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• Bulk inserting and updating with Entity Framework (Probably a better alternative?)

  - by Dave

  I have a data set of devices, addresses, and companies that I need to import into our database, with the catch that our database may already include a specific device/address/company that is included in the new data set. If that is the case, I need to update that entry with the new information in the data set, excluding addresses. We check if an exact copy of that address exists, otherwise we make a new entry. My issue is that it is very slow to attempt to grab a device/company in EF and if it exist updated it, otherwise insert it. To fix this I tried to get all the companies, devices, and addresses and insert them into respective hashmaps, and check if the identifier of the new data exists in the hashmap. This hasn't led to any performance increases. I've included my code below. Typically I would do a batch insert, I'm not sure what I would do for a batch update though. Can someone advise a different route? var context = ObjectContextHelper.CurrentObjectContext; var oldDevices = context.Devices; var companies = context.Companies; var addresses = context.Addresses; Dictionary<string, Company> companyMap = new Dictionary<string, Company>(StringComparer.OrdinalIgnoreCase); Dictionary<string, Device> deviceMap = new Dictionary<string, Device>(StringComparer.OrdinalIgnoreCase); Dictionary<string, Address> addressMap = new Dictionary<string, Address>(StringComparer.OrdinalIgnoreCase); foreach (Company c in companies) { if (c.CompanyAccountID != null && !companyMap.ContainsKey(c.CompanyAccountID)) companyMap.Add(c.CompanyAccountID, c); } foreach (Device d in oldDevices) { if (d.SerialNumber != null && !deviceMap.ContainsKey(d.SerialNumber)) deviceMap.Add(d.SerialNumber, d); } foreach (Address a in addresses) { string identifier = GetAddressIdentifier(a); if (!addressMap.ContainsKey(identifier)) addressMap.Add(identifier, a); } foreach (DeviceData.TabsDevice device in devices) { // update a device Company tempCompany; Address tempAddress; Device currentDevice; if (deviceMap.ContainsKey(device.SerialNumber)) //update a device deviceMap.TryGetValue(device.SerialNumber, out currentDevice); else // insert a new device currentDevice = new Device(); currentDevice.SerialNumber = device.SerialNumber; currentDevice.SerialNumberTABS = device.SerialNumberTabs; currentDevice.Model = device.Model; if (device.CustomerAccountID != null && device.CustomerAccountID != "") { companyMap.TryGetValue(device.CustomerAccountID, out tempCompany); currentDevice.CustomerID = tempCompany.CompanyID; currentDevice.CustomerName = tempCompany.CompanyName; } if (companyMap.TryGetValue(device.ServicingDealerAccountID, out tempCompany)) currentDevice.CompanyID = tempCompany.CompanyID; currentDevice.StatusID = 1; currentDevice.Retries = 0; currentDevice.ControllerFamilyID = 1; if (currentDevice.EWBFrontPanelMsgOption == null) // set the Panel option to the default if it isn't set already currentDevice.EWBFrontPanelMsgOption = context.EWBFrontPanelMsgOptions.Where( i => i.OptionDescription.Contains("default")).Single(); // link the device to the existing address as long as it is actually an address if (addressMap.TryGetValue(GetAddressIdentifier(device.address), out tempAddress)) { if (GetAddressIdentifier(device.address) != "") currentDevice.Address = tempAddress; else currentDevice.Address = null; } else // insert a new Address and link the device to it (if not null) { if (GetAddressIdentifier(device.address) == "") currentDevice.Address = null; else { tempAddress = new Address(); tempAddress.Address1 = device.address.Address1; tempAddress.Address2 = device.address.Address2; tempAddress.Address3 = device.address.Address3; tempAddress.Address4 = device.address.Address4; tempAddress.City = device.address.City; tempAddress.Country = device.address.Country; tempAddress.PostalCode = device.address.PostalCode; tempAddress.State = device.address.State; addresses.AddObject(tempAddress); addressMap.Add(GetAddressIdentifier(tempAddress), tempAddress); currentDevice.Address = tempAddress; } } if (!deviceMap.ContainsKey(device.SerialNumber)) // if inserting, add to context { oldDevices.AddObject(currentDevice); deviceMap.Add(device.SerialNumber, currentDevice); } } context.SaveChanges();

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• Same query has nested loops when used with INSERT, but Hash Match without.

  - by AaronLS

  I have two tables, one has about 1500 records and the other has about 300000 child records. About a 1:200 ratio. I stage the parent table to a staging table, SomeParentTable_Staging, and then I stage all of it's child records, but I only want the ones that are related to the records I staged in the parent table. So I use the below query to perform this staging by joining with the parent tables staged data. --Stage child records INSERT INTO [dbo].[SomeChildTable_Staging] ([SomeChildTableId] ,[SomeParentTableId] ,SomeData1 ,SomeData2 ,SomeData3 ,SomeData4 ) SELECT [SomeChildTableId] ,D.[SomeParentTableId] ,SomeData1 ,SomeData2 ,SomeData3 ,SomeData4 FROM [dbo].[SomeChildTable] D INNER JOIN dbo.SomeParentTable_Staging I ON D.SomeParentTableID = I.SomeParentTableID; The execution plan indicates that the tables are being joined with a Nested Loop. When I run just the select portion of the query without the insert, the join is performed with Hash Match. So the select statement is the same, but in the context of an insert it uses the slower nested loop. I have added non-clustered index on the D.SomeParentTableID so that there is an index on both sides of the join. I.SomeParentTableID is a primary key with clustered index. Why does it use a nested loop for inserts that use a join? Is there a way to improve the performance of the join for the insert?

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• Maximum of averages

  - by Qtacz

  I'm supposed to get every departments average wage and only show the department with the highest average wage. I figured out this query, but it doesn't work. Anyone got some ideas? SELECT department, max(avg(wage)) FROM employees GROUP BY department; I get this error: ERROR at line 1: ORA-00937: not a single-group group function

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• Postback Removing Styling from Page

  - by Roy

  Hi, Currently I've created a ASP.Net page that has a dropdown control with autopostback set to true. I've also added color backgrounds for individual listitems. Whenever an item is selected in the dropdown control the styling is completely removed from all of the list items. How can I prevent this from happening? I need the postback to pull data based on the dropdown item that is selected. Here is my code. aspx file: <asp:DropDownList ID="EmpDropDown" AutoPostBack="True" OnSelectedIndexChanged="EmpDropDown_SelectedIndexChanged" runat="server"> </asp:DropDownList> <asp:TextBox ID="MessageTextBox" TextMode="MultiLine" Width="550" Height="100px" runat="server"></asp:TextBox> aspx.cs code behind: protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { GetEmpList(); } } protected void EmpDropDown_SelectedIndexChanged(object sender, EventArgs e) { GetEmpDetails(); } private void GetEmpList() { SqlDataReader dr = ToolsLayer.GetEmpList(); int currentIndex = 0; while (dr.Read()) { EmpDropDown.Items.Add(new ListItem(dr["Title"].ToString(), dr["EmpKey"].ToString())); if (dr["Status"].ToString() == "disabled") { EmpDropDown.Items[currentIndex].Attributes.Add("style", "background-color:red;"); } currentIndex++; } dr.Close(); } private void GetEmpDetails() { SqlDataReader dr = ToolsLayer.GetEmpDetails(EmpDropDown.SelectedValue); while (dr.Read()) { MessageTextBox.Text = dr["Message"].ToString(); } dr.Close(); } Thank You

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• Primary key/foreign Key naming convention

  - by Jeremy

  In our dev group we have a raging debate regarding the naming convention for Primary and Foreign Keys. There's basically two schools of thought in our group: 1) Primary Table (Employee) Primary Key is called ID Foreign table (Event) Foreign key is called EmployeeID 2) Primary Table (Employee) Primary Key is called EmployeeID Foreign table (Event) Foreign key is called EmployeeID I prefer not to duplicate the name of the table in any of the columns (So I prefer option 1 above). Conceptually, it is consisted with a lot of the recommended practices in other languages, where you don't use the name of the object in its property names. I think that naming the foreign key EmployeeID (or Employee_ID might be better) tells the reader that it is the ID column of the Employee Table. Some others prefer option 2 where you name the primary key prefixed with the table name so that the column name is the same throughout the database. I see that point, but you now can not visually distinguish a primary key from a foreign key. Also, I think it's redundant to have the table name in the column name, because if you think of the table as an entity and a column as a property or attribute of that entity, you think of it as the ID attribute of the Employee, not the EmployeeID attribute of an employee. I don't go an ask my coworker what his PersonAge or PersonGender is. I ask him what his Age is. So like I said, it's a raging debate and we go on and on and on about it. I'm interested to get some new perspective.

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• A table that has relation to itself issue

  - by Mostafa

  Hi , I've defined table with this schema : CREATE TABLE [dbo].[Codings]( [Id] [int] IDENTITY(1,1) NOT NULL, [ParentId] [int] NULL, [CodeId] [int] NOT NULL, [Title] [nvarchar](50) COLLATE Arabic_CI_AI NOT NULL, CONSTRAINT [PK_Codings] PRIMARY KEY CLUSTERED ( [Id] ASC )WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY] ) ON [PRIMARY] And fill it up with data like this : Id ParentId CodeId Title ----------- ----------- ----------- ---------- 1 NULL 0 Gender 2 1 1 Male 3 1 2 Female 4 NULL 0 Educational Level 5 4 1 BS 6 4 2 MS 7 4 3 PHD Now , I'm looking for a solution , in order , When i delete a record that is parent ( like Id= 1 or 4 ), It delete all child automatically ( all records that their ParentId is 1 or 4 ) . I supposed i can do it via relation between Id and Parent Id ( and set cascade for delete rule ) , But when i do that in MMS , the Delete Rule or Update Rule in Properties is disabled . My question is , What can i do to accomplish this ? Thank you

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• WPF/.NET data access models - resource recommendations

  - by jasonk

  We're in the early design/prep phases of transferring/updating a rather large "legacy" 3 tier client-server app to a new version. We’re looking at doing WPF over Winforms as it appears to be the direction Microsoft is pushing development of the future and we’d like the maximize the life cycle/span of the apps. That said during the rewrite we’d like to make as many changes to our data access/presentation model to improve performance as much as possible up front as many. I’ve been doing some research along that vein but the vast majority of the resources I've found that discuss WPF focus only simple data tracking apps or focus on the very basics UI design/controls. The few items that even discuss data presentation are fairly elementary in depth. Are there any books/articles/recommended reading/other resources recommended for development related to large enterprise level business apps? Any “gotchas” that should/could be avoided? General advice to minimize the time underwater

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• How to make a stored procedure return the last inserted id

  - by Luke101

  Here I have a stored procedure that inserts a row but how do you make it return the last inserted id without making another query CREATE PROCEDURE [dbo].[spInsertCriteriaItem] @GroupID int AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; insert into CriteriaItem (CriteriaGroupID) VALUES(@GroupID) --I don't want to make another query here END Is it possible to do this

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• IN MSSQL 2008 is there a way to generate a report as to how much space on disk each table takes?

  - by Matt

  IN MSSQL 2008 is there a way to generate a report as to how much space on disk each table takes? I can do it one by one by checking the storage properties, but I was wondering if there was a way, maybe even a query to generate such a report.

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• Incorrect syntax inserting data into table

  - by SelectDistinct

  I am having some trouble with my update() method. The idea is that the user Provides a recipe name, ingredients, instructions and then selects an image using Filestream. Once the user clicks 'Add Recipe' this will call the update method, however as things stand I am getting an error which is mentioning the contents of the text box: Here is the update() method code: private void updatedata() { // filesteam object to read the image // full length of image to a byte array try { // try to see if the image has a valid path if (imagename != "") { FileStream fs; fs = new FileStream(@imagename, FileMode.Open, FileAccess.Read); // a byte array to read the image byte[] picbyte = new byte[fs.Length]; fs.Read(picbyte, 0, System.Convert.ToInt32(fs.Length)); fs.Close(); //open the database using odp.net and insert the lines string connstr = @"Server=mypcname\SQLEXPRESS;Database=RecipeOrganiser;Trusted_Connection=True"; SqlConnection conn = new SqlConnection(connstr); conn.Open(); string query; query = "insert into Recipes(RecipeName,RecipeImage,RecipeIngredients,RecipeInstructions) values (" + textBox1.Text + "," + " @pic" + "," + textBox2.Text + "," + textBox3.Text + ")"; SqlParameter picparameter = new SqlParameter(); picparameter.SqlDbType = SqlDbType.Image; picparameter.ParameterName = "pic"; picparameter.Value = picbyte; SqlCommand cmd = new SqlCommand(query, conn); cmd.Parameters.Add(picparameter); cmd.ExecuteNonQuery(); MessageBox.Show("Image successfully saved"); cmd.Dispose(); conn.Close(); conn.Dispose(); Connection(); } } catch (Exception ex) { MessageBox.Show(ex.Message); } } Can anyone see where I have gone wrong with the insert into Recipes query or suggest an alternative approach to this part of the code?

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• Copying a subset of data to an empty database with the same schema

  - by user193655

  I would like to export part of a database full of data to an empty database. Both databases has the same schema. I want to maintain referential integrity. To simplify my cases it is like this: MainTable has the following fields: 1) MainID integer PK 2) Description varchar(50) 3) ForeignKey integer FK to MainID of SecondaryTable SecondaryTable has the following fields: 4) MainID integer PK (referenced by (3)) 5) AnotherDescription varchar(50) The goal I'm trying to accomplish is "export all records from MainTable using a WHERE condition", for example all records where MainID < 100. To do it manually I shuold first export all data from SecondaryTable contained in this select: select * from SecondaryTable ST outer join PrimaryTable PT on ST.MainID=PT.MainID then export the needed records from MainTable: select * from MainTable where MainID < 100. This is manual, ok. Of course my case is much much much omre complex, I have 200+ tables, so donig it manually is painful/impossible, I have many cascading FKs. Is there a way to force the copy of main table only "enforcing referntial integrity". so that my query is something like: select * from MainTable where MainID < 100 WITH "COPYING ALL FK sources" In this cases also the field (5) will be copied. ====================================================== Is there a syntax or a tool to do this? Table per table I'd like to insert conditions (like MainID <100 is only for MainTable, but I have also other tables).

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• Implementing a 1 to many relationship with SQLite

  - by Patrick

  I have the following schema implemented successfully in my application. The application connects desk unit channels to IO unit channels. The DeskUnits and IOUnits tables are basically just a list of desk/IO units and the number of channels on each. For example a desk could be 4 or 12 channel. CREATE TABLE DeskUnits (Name TEXT, NumChannels NUMERIC); CREATE TABLE IOUnits (Name TEXT, NumChannels NUMERIC); CREATE TABLE RoutingTable (DeskUnitName TEXT, DeskUnitChannel NUMERIC, IOUnitName TEXT, IOUnitChannel NUMERIC); The RoutingTable 'table' then connects each DeskUnit channel to an IOUnit channel. For example the DeskUnit called "Desk1" channel 1 may route to IOunit name "IOUnit1" channel 2, etc. So far I hope this is pretty straightforward and understandable. The problem is, however, this is a strictly 1 to 1 relationship. Any DeskUnit channel can route to only 1 IOUnit channel. Now, I need to implement a 1 to many relationship. Where any DeskUnit channel can connect to multiple IOUnit channels. I realise I may have to rearrange the tables completely, but I am not sure the best way to go about this. I am fairly new to SQLite and databases in general so any help would be appreciated. Thanks Patrick

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• MSSQL in ASP.NET application getting unstable after a certain period

  - by Barslett

  Hello, I have an ASP.NET 2.0 application that I made to keep track of disruption reports about our public transport system. The architecture is pretty straight-forward; an MSSQL Express 2008 database, ADO.NET and a DataSet/DAL with a few methods to access the database. There is a set of .aspx pages for the UI in use by our dispatchers and on our public website, as well as a set of SOAP and REST webservices and an RSS feed. Everything worked just fine for more than a year, until two weeks ago. Now and then, it seems as the database enters an unstable mode, and the application starts responding something right, something wrong. The typical error is that apparently, an empty DataTable is returned to the public disruption overview or to the RSS generator. Thus, the user gets e.g. an empty GridView, but no exception is thrown AFAIK, and nothing is written to the Windows Application log. After a restart of the MSSQL Express service, the situation is back to normal. It has to be said that the situation first time appeared a few days after I made a new minor upgrade of the application. The RSS generator was slightly rewritten, and I added a WCF REST service. But the DAL and the database schema were untouched... Any hints of how we could keep the database stable? It is a bit annoying not to have a clue ;-)

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• Selecting rows without a value for Date/Time columns

  - by Ross

  I'm running this query: SELECT TOP 1 [DVD Copy].[Stock No] FROM [DVD Copy] WHERE [DVD Copy].[Catalogue No] =[Forms]![New Rental]![Catalogue No] And [Issue Date] = Null; Which works fine without the null check for Issue Date. I'm trying to select rows without a Date in the Issue Date column. Is Null the wrong kind of value to use for here?

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• Can't add domain users to Reporting Services 2008

  - by Jeremy

  I have SSRS 2008 setup on the database server. The server is part of the domain. Reporting Services is running under NetworkService. When I try to add a domain user using the web interface (Site Settings -- Security -- New Role Assignment), the page posts back but the user is not in the list. The server's log file contains the following Unhandled Exception: ui!ReportManager_0-1!954!01/12/2009-10:14:52:: Unhandled exception: System.Security.Principal.IdentityNotMappedException: Some or all identity references could not be translated. at System.Security.Principal.SecurityIdentifier.Translate(IdentityReferenceCollection sourceSids, Type targetType, Boolean forceSuccess) at System.Security.Principal.SecurityIdentifier.Translate(Type targetType) at System.Security.Principal.WindowsIdentity.GetName() at System.Security.Principal.WindowsIdentity.get_Name() at ReportingServicesHttpRuntime.RsWorkerRequest.GetServerVariable(String name) at System.Web.Security.WindowsAuthenticationModule.OnEnter(Object source, EventArgs eventArgs) at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) Any one have an idea on how to fix this?

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• RDLC item width is dynamic and causing extra pages to be generated (image included)?

  - by Paul Mendoza

  I'm trying to format an RDLC report file in Visual Studio 2008 and I am having a formatting issue. I have a list at the bottom that contains a matrix that expands horizontally to the right. That pink box is just to visualize the problem I'm having. When the report is rendered the matrix expands and instead of filling the pink box with the matrix is pushes the space in the pink box to the right resulting in an extra page when printing the reports. One solution would be to shrink the pink box to be the size of the matrix which I've done. But then when the matrix grows the fields at the top of the report get pushed to the right by the same amount as the growth of the matrix. Can someone please let me know what they think the solution would be? Thank you!

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• Non-Access or -base QBE tool?

  - by idbin.cath0br0

  Hello. I'm currently looking for a QBE tool that can execute queries on PostgreSQL or MySQL. OS doesn't really matter. Reason is that we've got to do QBE at school but I don't want to use neither Microsoft Access nor OpenOffice.org Base (lack of features). Any help would be appreciated.

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• COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better?

  - by zneak

  Hello guys, I often find these three variants: SELECT COUNT(*) FROM Foo; SELECT COUNT(1) FROM Foo; SELECT COUNT(PrimaryKey) FROM Foo; As far as I can see, they all do the same thing, and I find myself using the three in my codebase. However, I don't like to do the same thing different ways. To which one should I stick? Is any one of them better than the two others?

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• How to skip all the column names in MySQL when the table has auto increment primary key?

  - by Jian Lin

  A table is: mysql> desc gifts; +---------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+----------------+ | giftID | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(80) | YES | | NULL | | | filename | varchar(80) | YES | | NULL | | | effectiveTime | datetime | YES | | NULL | | +---------------+-------------+------+-----+---------+----------------+ the following is ok: mysql> insert into gifts -> values (10, "heart", "heart_shape.jpg", now()); Query OK, 1 row affected (0.05 sec) but is there a way to not specify the "10"... and just let each one be 11, 12, 13... ? I can do it using mysql> insert into gifts (name, filename, effectiveTime) -> values ("coffee", "coffee123.jpg", now()); Query OK, 1 row affected (0.00 sec) but the column names need to be all specified. Is there a way that they don't have to be specified and the auto increment of primary key still works? thanks.

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• How to stop looking in a database after X rows are found?

  - by morningface

  I have a query to a database that returns a number X of results. I am looking to return a maximum of 10 results. Is there a way to do this without using LIMIT 0,9? I'll use LIMIT if I have to, but I'd rather use something else that will literally stop the searching, rather than look at all rows and then only return the top 10.

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• I would like to make a field part of a many to many relationship

  - by jona

  I have the following table called stores id store zip 1 Market 1 01569 2 Market 2 01551 3 Market 3 10468 4 Market 4 10435 Zip code table INSERT INTO `zip_codes` (`restaurants_locations_id`, `zip`, `state`, `latitude`, `longitude`, `city`, `full_state`) VALUES (1, '06001', 'CT', ' 41.789698', ' -72.86431', 'Avon', 'Connecticut'), (2, '06002', 'CT', ' 41.832798', ' -72.72642', 'Bloomfield', 'Connecticut'), (3, '06010', 'CT', ' 41.682249', ' -72.93365', 'Bristol', 'Connecticut'), (4, '06013', 'CT', ' 41.758415', ' -72.94642', 'Burlington', 'Connecticut'), (5, '06016', 'CT', ' 41.909097', ' -72.54393', 'Windsorville', 'Connecticut'), (6, '06018', 'CT', ' 42.023510', ' -73.31103', 'Canaan', 'Connecticut'), (7, '06019', 'CT', ' 41.834247', ' -72.89174', 'Canton', 'Connecticut'), etc.... what I want is to create a table which will connect the zip field in the stores tables where one store will be found in several zicodes... How would that table would look like? Thanks

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• Selecting an element based on class and id in jquery - similar to an SQL query

  - by Ankur

  I want to select an element based on it's class and id, I have seen many similar questions on SO. Most of the users ask why would you ever want to do this - which is not very helpful, trust me, this is the simplest way of solving my UI problem, and it's a very unique and intereting UI related to making generic triple stores easily browsable. At the moment the jQUery looks like this: $(document).ready( function() { $(".predicates").hide(); $(".objects").hide(); $("#subject").click( function() { $("#predId, .predicates").toggle(); // this line } ); $("#predId").click( function() { $("#objId, .objects").toggle(); } ); }); The line I am really interested in is this $("#predId, .predicates").toggle(); how do I get the select to ensure that both #predId and .predicates are true, at the moment it seems that only one or the other has to be true. Is there something like an && operator?

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• IN statement performance in PostgreSQL (and in general)

  - by Vasil

  I know this has probably been asked before, but I can't find it with SO's search. Lets say i've TABLE1 and TABLE2, who should I expect the performance of a query such as this: SELECT * FROM TABLE1 WHERE id IN SUBQUERY_ON_TABLE2; as the number of rows in TABLE1 and TABLE2 grow and id is a primary key on TABLE1. Yes, I know using IN is such a n00b mistake, but TABLE2 has a generic relation (django generic relation) to multiple other tables so I can't think of another way to filter the data. At what (aproximate) ammount of rows in TABLE1 and TABLE2 should I expect to notice performance issues because of this? Will performance degrade linearly, exponentially etc. depending on the number of rows?

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• Ordering by a max or a min from another table

  - by Paul Tomblin

  I have a table that consists of a unique id, and a few other attributes. It holds "schedules". Then I have another table that holds a list of all the times each schedule has or will "fire". This isn't the exact schema, but it's close: create table schedule ( id varchar(40) primary key, attr1 int, attr2 varchar(20) ); create table schedule_times ( id varchar(40) foreign key schedule(id), fire_date date ); I want to query the schedule table, getting the attributes and the next and previous fire_dates, in Java, sometimes ordering on one of the attributes, but sometimes ordering on either previous fire_date or the next fire_date. Ordering by the attributes is easy, I just stick an "order by" into the string while I'm building my prepared statement. I'm not even sure how to go about selecting the last fire_date and the next one in a single query - I know that I can find the next fire_date for a given id by doing a SELECT min(fire_date) FROM schedule_times WHERE id = ? AND fire_date > sysdate; and the similar thing for previous fire_date using max() and fire_date < sysdate. I'm just drawing a blank on how to incorporate that into a single select from the schedule so I can get both next and previous fire_date in one shot, and also how to order by either of those attributes.

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