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• How to get the last element by date of each "type" in LINQ or TSQL

  - by Mauro

  Imagine to have a table defined as CREATE TABLE [dbo].[Price]( [ID] [int] NOT NULL, [StartDate] [datetime] NOT NULL, [Price] [int] NOT NULL ) where ID is the identifier of an action having a certain Price. This price can be updated if necessary by adding a new line with the same ID, different Price, and a more recent date. So with a set of a data like ID StartDate Price 1 01/01/2009 10 1 01/01/2010 20 2 01/01/2009 10 2 01/01/2010 20 How to obtain a set like the following? 1 01/01/2010 20 2 01/01/2010 20

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• Nullable Integer ? (working with linq)

  - by nCdy

  I've got exception about convert NULL to Int32. I've got a table from database with nullable tinyint [Column(Storage="_StatType", DbType="tinyint NULL")] public StatType : int { get { _StatType; } } (to get C# code just replace variable's type) and after making linq select def StartLinq = linq <#from lpi in _CfgListParIzm where lpi.ID_ListParIzm==drr1 select (lpi.StatType) #> ; StartLinq.ToArray()[0] can't be readed if that is null :-/ mutable STT : int = 0; try { _=int.TryParse(StartLinq.ToArray()[0].ToString(), out STT); } catch { | _ is Exception => () /* I don't care*/ } upper code is very poor trick :( I wont use it.

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• Self-referencing tables in Linq2Sql

  - by J-Man

  Hi, I've seen a lot of questions on self-referencing tables in Linq2Sql and how to eagerly load all child records for a particular root object. I've implemented a temporary solution by accessing all underlying properties, but you can see that this doesn't do the performance any good. The thing is though, that all records are correlated with each-other using a correlation GUID. Example below: RootElement - Id: 1 - ParentId: null - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement1 - Id: 2 - ParentId: 1 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement2 - Id: 3 - ParentId: 2 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD ChildElement1 - Id: 4 - ParentId: 2 - CorrelationId: 4D68E512-4B55-44f4-BA5A-174B630A03DD In my case, I do have access to the correlationId, so I can retrieve all of my records by performing the following query: from element in db.Elements where element.CorrelationId == '4D68E512-4B55-44f4-BA5A-174B630A03DD' select element; But, of course, I want these elements associated with each other by executing this query: from element in db.Elements where element.CorrelationId == '4D68E512-4B55-44f4-BA5A-174B630A03DD' && element.ParentId == null select element; My question is: is it possible to combine the results the first query as some sort of 'caching mechanism' for the query where I get the root element? Thanks for the input. J.

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• Historical / auditable database

  - by Mark

  Hi all, This question is related to the schema that can be found in one of my other questions here. Basically in my database I store users, locations, sensors amongst other things. All of these things are editable in the system by users, and deletable. However - when an item is edited or deleted I need to store the old data; I need to be able to see what the data was before the change. There are also non-editable items in the database, such as "readings". They are more of a log really. Readings are logged against sensors, because its the reading for a particular sensor. If I generate a report of readings, I need to be able to see what the attributes for a location or sensor was at the time of the reading. Basically I should be able to reconstruct the data for any point in time. Now, I've done this before and got it working well by adding the following columns to each editable table: valid_from valid_to edited_by If valid_to = 9999-12-31 23:59:59 then that's the current record. If valid_to equals valid_from, then the record is deleted. However, I was never happy with the triggers I needed to use to enforce foreign key consistency. I can possibly avoid triggers by using the extension to the "PostgreSQL" database. This provides a column type called "period" which allows you to store a period of time between two dates, and then allows you to do CHECK constraints to prevent overlapping periods. That might be an answer. I am wondering though if there is another way. I've seen people mention using special historical tables, but I don't really like the thought of maintainling 2 tables for almost every 1 table (though it still might be a possibility). Maybe I could cut down my initial implementation to not bother checking the consistency of records that aren't "current" - i.e. only bother to check constraints on records where the valid_to is 9999-12-31 23:59:59. Afterall, the people who use historical tables do not seem to have constraint checks on those tables (for the same reason, you'd need triggers). Does anyone have any thoughts about this? PS - the title also mentions auditable database. In the previous system I mentioned, there is always the edited_by field. This allowed all changes to be tracked so we could always see who changed a record. Not sure how much difference that might make. Thanks.

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• LINQ: Create persistable Associations in Code, Without Foreign Key

  - by Alex

  Hello, I know that I can create LINQ Associations without a Foreign Key. The problem is, I've been doing this by adding the [Association] attribute in the DBML file (same as through the designer), which will get erased again after I refresh my database (and reload the entire table structure). I know that there is the MyData.cs file (as part of the DBML) in which I can place my partial extensions etc. to domain objects (to persist even after I refresh the DBML), but I don't know how to create an association there?

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• One table, need multiple values from different rows/tuples

  - by WmasterJ

  I have tables like: 'profile_values' userID | fid | value -------+---------+------- 1 | 3 | [email protected] 1 | 45 | 203-234-2345 3 | 3 | [email protected] 1 | 45 | 123-456-7890 And: 'users' userID | name -------+------- 1 | joe 2 | jane 3 | jake I want to join them and have one row with two of the values like: 'profile_values' userID | name | email | phone -------+-------+----------------+-------------- 1 | joe | [email protected] | 203-234-2345 2 | jane | [email protected] | 123-456-7890 I have solved it but it feels clumsy and I want to know if there is a better way to do it. Meaning solutions that are either more readable or faster(optimized) or simply best-practice. Current solution: multiple tables selected, many conditional statements: SELECT u.userID AS memberid, u.name AS first_name, pv1.value AS fname, pv2.value as lname FROM users AS u, profile_values AS pv1, profile_values AS pv2, WHERE u.userID = pv1.userID AND pv1.fid = 3 AND u.userID = pv2.userID AND pv2.fid = 45; Thanks for the help!

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• Table Partitioning

  - by Ankur Gahlot

  How advantageous is it to use partitioning of tables as compared to normal approach ? Is there a sort of sample case or detailed comparative analysis that could statistically ( i know this is too strong a word, but it would really help if it is illustrated by some numbers ) emphasize on the utility of the process. Thanks, Ankur

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• Why index_merge is not used here?

  - by user198729

  Setup: mysql> create table t(a integer unsigned,b integer unsigned); mysql> insert into t(a,b) values (1,2),(1,3),(2,4); mysql> create index i_t_a on t(a); mysql> create index i_t_b on t(b); mysql> explain select * from t where a=1 or b=4; +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | t | ALL | i_t_a,i_t_b | NULL | NULL | NULL | 3 | Using where | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ Is there something I'm missing?

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• how to show partial key in uml er diagram

  - by Infestor

  in chen's notation partial keys were shown as dashed lines, how are they shown in uml er (entity-relationship) diagram?

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• PHP Error - Login Script

  - by gamerzfuse

  I am creating a new login script/members directory. I am creating it from scratch without any frameworks (advice on this matter would also be appreciated). The situation: // Look up the username and password in the database $query = "SELECT admin_id, username FROM admin WHERE adminname = '$admin_user' AND password = SHA1('$admin_pass')"; $data = mysqli_query($dbc, $query); if (mysqli_num_rows($data) == 1) { This bit of code keeps giving me an error (the last line in particular): Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in /home8/craighoo/public_html/employees/security/dir_admin.php on line 20 When echoing the query I get: SELECT admin_id, username FROM admin WHERE adminname = 'admin' AND password = SHA1('tera#byte') Thanks in advance!

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• Trouble with LINQ databind to GridView and RowDataBound

  - by Michael

  Greetings all, I am working on redesigning my personal Web site using VS 2008 and have chosen to use LINQ to create by data-access layer. Part of my site will be a little app to help manage my budget better. My first LINQ query does successfully execute and display in a GridView, but when I try to use a RowDataBound event to work with the results and refine them a bit, I get the error: The type or namespace name 'var' could not be found (are you missing a using directive or an assembly reference?) This interesting part is, if I just try to put in a var s = "s"; anywhere else in the same file, I get the same error too. If I go to other files in the web project, var s = "s"; compiles fine. Here is the LINQ Query call: public static IQueryable pubGetRecentTransactions(int param_accountid) { clsDataContext db; db = new clsDataContext(); var query = from d in db.tblMoneyTransactions join p in db.tblMoneyTransactions on d.iParentTransID equals p.iTransID into dp from p in dp.DefaultIfEmpty() where d.iAccountID == param_accountid orderby d.dtTransDate descending, d.iTransID ascending select new { d.iTransID, d.dtTransDate, sTransDesc = p != null ? p.sTransDesc : d.sTransDesc, d.sTransMemo, d.mTransAmt, d.iCheckNum, d.iParentTransID, d.iReconciled, d.bIsTransfer }; return query; } protected void Page_Load(object sender, EventArgs e) { if (!this.IsPostBack) { this.prvLoadData(); } } internal void prvLoadData() { prvCtlGridTransactions.DataSource = clsMoneyTransactions.pubGetRecentTransactions(2); prvCtlGridTransactions.DataBind(); } protected void prvCtlGridTransactions_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { var datarow = e.Row.DataItem; var s = "s"; e.Row.Cells[0].Text = datarow.dtTransDate.ToShortDateString(); e.Row.Cells[1].Text = datarow.sTransDesc; e.Row.Cells[2].Text = datarow.mTransAmt.ToString("c"); e.Row.Cells[3].Text = datarow.iReconciled.ToString(); }//end if }//end RowDataBound My googling to date hasn't found a good answer, so I turn it over to this trusted community. I appreciate your time in assisting me.

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• Sqlite View : Add a column based on some other column

  - by NightCoder

  Hi, I have two tables Employee ID | Name | Department ---------------------- 121 |Name1 | dep1 223 |Name2 | dep2 Assignment ID | EID| --------- 1 |121 2 |223 3 |121 [other columns omitted for brevity] The table assignment indicates which is work is assigned to whom.EID is a foriegn key to the table Employee.Also it is possible to have two work assigned to the same employee. Now i want to create a view like this EID | Assigned -------------- 121 |true 333 |false Assigned column should be calculated based on the entries in the Assignment table. So far i am only successful in creating a view like this EID | Assigned -------------- 121 |2 333 |0 using the command CREATE VIEW "AssignmentView" AS SELECT distinct ID ,(select Count(*) from Assignment where Assignment.EID = Employee.ID) as Assigned FROM Employee; Thanks

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• Count times ID appears in a table and return in row.

  - by Tyler

  SELECT Boats.id, Boats.date, Boats.section, Boats.raft, river_company.company, river_section.section AS river FROM Boats INNER JOIN river_company ON Boats.raft = river_company.id INNER JOIN river_section ON Boats.section = river_section.id ORDER BY Boats.date DESC, river, river_company.company Returns everything I need. But how would I add a [Photos] table and count how many times Boats.id occurs in it and add that to the returned rows. So if there are 5 photos for boat #17 I want the record for boat #17 to say PhotoCount = 5

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• Programming /open source [closed]

  - by Ahsan Bagwan

  I m a CS UG student, and want to know how to participate in open source projects. Which one will be good for beginner in C, or Java?

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• Is my understanding of "select distinct" correct?

  - by paxdiablo

  We recently discovered a performance problem with one of our systems and I think I have the fix but I'm not certain my understanding is correct. In simplest form, we have a table blah into which we accumulate various values based on a key field. The basic form is: recdate date rectime time system varchar(20) count integer accum1 integer accum2 integer There are a lot more accumulators than that but they're all of the same form. The primary key is made up of recdate, rectime and system. As values are collected to the table, the count for a given recdate/rectime/system is incremented and the values for that key are added to the accumulators. That means the averages can be obtained by using accumN / count. Now we also have a view over that table specified as follows: create view blah_v ( recdate, rectime, system, count, accum1, accum2 ) as select distinct recdate, rectime, system, count, value (case when count > 0 then accum1 / count end, 0), value (case when count > 0 then accum2 / count end, 0) from blah; In other words, the view gives us the average value of the accumulators rather than the sums. It also makes sure we don't get a divide-by-zero in those cases where the count is zero (these records do exist and we are not allowed to remove them so don't bother telling me they're rubbish - you're preaching to the choir). We've noticed that the time difference between doing: select distinct recdate from XX varies greatly depending on whether we use the table or the view. I'm talking about the difference being 1 second for the table and 27 seconds for the view (with 100K rows). We actually tracked it back to the select distinct. What seems to be happening is that the DBMS is actually loading all the rows in and sorting them so as to remove duplicates. That's fair enough, it's what we stupidly told it to do. But I'm pretty sure the fact that the view includes every component of the primary key means that it's impossible to have duplicates anyway. We've validated the problem since, if we create another view without the distinct, it performs at the same speed as the underlying table. I just wanted to confirm my understanding that a select distinct can not have duplicates if it includes all the primary key components. If that's so, then we can simply change the view appropriately.

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• asp.net mvc insert doesnt seem to work for me....

  - by Pandiya Chendur

  My controller's call to repository insert method all the values are passed but it doesn't get inserted in my table.. My controller method, [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create([Bind(Exclude = "Id")]FormCollection collection) { try { MaterialsObj materialsObj = new MaterialsObj(); materialsObj.Mat_Name = collection["Mat_Name"]; materialsObj.Mes_Id = Convert.ToInt64(collection["MeasurementType"]); materialsObj.Mes_Name = collection["Mat_Type"]; materialsObj.CreatedDate = System.DateTime.Now; materialsObj.CreatedBy = Convert.ToInt64(1); materialsObj.IsDeleted = Convert.ToInt64(1); consRepository.createMaterials(materialsObj); return RedirectToAction("Index"); } catch { return View(); } } and my repository, public MaterialsObj createMaterials(MaterialsObj materialsObj) { Material mat = new Material(); mat.Mat_Name = materialsObj.Mat_Name; mat.Mat_Type = materialsObj.Mes_Name; mat.MeasurementTypeId = materialsObj.Mes_Id; mat.Created_Date = materialsObj.CreatedDate; mat.Created_By = materialsObj.CreatedBy; mat.Is_Deleted = materialsObj.IsDeleted; db.Materials.InsertOnSubmit(mat); return materialsObj; } What am i missing here any suggestion....

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• Applying Domain Model on top of Linq2Sql entities

  - by Thomas

  I am trying to practice the model first approach and I am putting together a domain model. My requirement is pretty simple: UserSession can have multiple ShoppingCartItems. I should start off by saying that I am going to apply the domain model interfaces to Linq2Sql generated entities (using partial classes). My requirement translates into three database tables (UserSession, Product, ShoppingCartItem where ProductId and UserSessionId are foreign keys in the ShoppingCartItem table). Linq2Sql generates these entities for me. I know I shouldn't even be dealing with the database at this point but I think it is important to mention. The aggregate root is UserSession as a ShoppingCartItem can not exist without a UserSession but I am unclear on the rest. What about Product? It is defiently an entity but should it be associated to ShoppingCartItem? Here are a few suggestion (they might all be incorrect implementations): public interface IUserSession { public Guid Id { get; set; } public IList<IShoppingCartItem> ShoppingCartItems{ get; set; } } public interface IShoppingCartItem { public Guid UserSessionId { get; set; } public int ProductId { get; set; } } Another one would be: public interface IUserSession { public Guid Id { get; set; } public IList<IShoppingCartItem> ShoppingCartItems{ get; set; } } public interface IShoppingCartItem { public Guid UserSessionId { get; set; } public IProduct Product { get; set; } } A third one is: public interface IUserSession { public Guid Id { get; set; } public IList<IShoppingCartItemColletion> ShoppingCartItems{ get; set; } } public interface IShoppingCartItemColletion { public IUserSession UserSession { get; set; } public IProduct Product { get; set; } } public interface IProduct { public int ProductId { get; set; } } I have a feeling my mind is too tightly coupled with database models and tables which is making this hard to grasp. Anyone care to decouple?

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• Acquiring Table Lock in Database - Interview Question

  - by harigm

  One of my interview Questions, if multiple users across the world are accessing the application, in which it uses a Table which has a Primary Key as Auto Increment Field. The Question how can you prevent the other user getting the Same Primary key when the other user is executing? My answer was I will obtain the Lock on the table and I will make the user to wait Until that user is released with the Primary key. But the Question How do you acquire the Table lock programmatically and implement this? If there are 1000 users coming every minute to the application, if you explicity hold the lock on the table, then the application will become slower? How do you manage this? Please suggest the possible answers for the above question

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• MySQL optimized sentence

  - by Ivan

  I have a simple table where I have to extract some records. The problem is that the evaluation function is a very time-consuming stored procedure so I shouldn't to call it twice like in this sentence: SELECT *, slow_sp(row) FROM table WHERE slow_sp(row)>0 ORDER BY dist DESC LIMIT 10 First I thought in optimize like this: SELECT *, slow_sp(row) AS value FROM table WHERE value>0 ORDER BY dist DESC LIMIT 10 But it doesn't works due "value" is not processed when the WHERE clause is evaluated. Any idea to optimize this sentence? Thanks.

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• Bus Timetable database design

  - by paddydub

  hi, I'm trying to design a db to store the timetable for 300 different bus routes, Each route has a different number of stops and different times for Monday-Friday, Saturday and Sunday. I've represented the bus departure times for each route as follows, I'm not sure if i should have null values in the table, does this look ok? route,Num,Day, t1, t2, t3, t4 t5 t6 t7 t8 t9 t10 117, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 null null null 117, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 null null null 117, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 null null null 117, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 null null null . . . 117, 20, Monday, 9:39, 10.09, 11:39, 12:39, 14:39 18:39 19:39 null null null 119, 1, Monday, 9:00, 9:30, 10:50, 12:00, 14:00 18:00 19:00 20:00 21:00 22:00 119, 2, Monday, 9:03, 9:33, 10:53, 12:03, 14:03 18:03 19:03 20:03 21:03 22:03 119, 3, Monday, 9:06, 9:36, 10:56, 12:06, 14:06 18:06 19:06 20:06 21:06 22:06 119, 4, Monday, 9:09, 9:39, 10:59, 12:09, 14:09 18:09 19:09 20:09 21:09 22:09 . . . 119, 37, Monday, 9:49, 9:59, 11:59, 12:59, 14:59 18:59 19:59 20:59 21:59 22:59 139, 1, Sunday, 9:00, 9:30, 20:00 21:00 22:00 null null null null null 139, 2, Sunday, 9:03, 9:33, 20:03 21:03 22:03 null null null null null 139, 3, Sunday, 9:06, 9:36, 20:06 21:06 22:06 null null null null null 139, 4, Sunday, 9:09, 9:39, 20:09 21:09 22:09 null null null null null . . . 139, 20, Sunday, 9:49, 9:59, 20:59 21:59 22:59 null null null null null

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• Testing the context in asp.net mvc

  - by user252160

  I got pretty experienced with testing controllers, my question here is though, aren't we supposed to test the data context as well, and how ? I mean, there are a lot of relationships and constraints coming from the DB that simply testing controllers does not cover. On the other hand, testing against the DB is not considered a good practice - what then ? Simply testing without db.SubmitChanges() or what ?

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• ALTER TABLE on dependant column

  - by Sharmi

  I am trying to alter column datatype of a primary key to tinyint from int.This column is a foreign key in other tables.So,I get the following error: Msg 5074, Level 16, State 1, Line 1 The object 'PK_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Details_tbl_User_tbl' is dependent on column 'appId'. Msg 5074, Level 16, State 1, Line 1 The object 'FK_Log_tbl_User_tbl' is dependent on column 'appId'. Msg 4922, Level 16, State 9, Line 1 ALTER TABLE ALTER COLUMN appId failed because one or more objects access this column. Howw should i rectify this?

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• Problem with interface implementation in partial classes.

  - by Bas

  I have a question regarding a problem with L2S, Autogenerated DataContext and the use of Partial Classes. I have abstracted my datacontext and for every table I use, I'm implementing a class with an interface. In the code below you can see I have the Interface and two partial classes. The first class is just there to make sure the class in the auto-generated datacontext inherets Interface. The other autogenerated class makes sure the method from Interface is implemented. namespace PartialProject.objects { public interface Interface { Interface Instance { get; } } //To make sure the autogenerated code inherits Interface public partial class Class : Interface { } //This is autogenerated public partial class Class { public Class Instance { get { return this.Instance; } } } } Now my problem is that the method implemented in the autogenerated class gives the following error: - Property 'Instance' cannot implement property from interface 'PartialProject.objects.Interface'. Type should be 'PartialProjects.objects.Interface'. <- Any idea how this error can be resolved? Keep in mind that I can't edit anything in the autogenerated code. Thanks in advance!

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• Representing Sparse Data in PostgreSQL

  - by Chris S

  What's the best way to represent a sparse data matrix in PostgreSQL? The two obvious methods I see are: Store data in a single a table with a separate column for every conceivable feature (potentially millions), but with a default value of NULL for unused features. This is conceptually very simple, but I know that with most RDMS implementations, that this is typically very inefficient, since the NULL values ususually takes up some space. However, I read an article (can't find its link unfortunately) that claimed PG doesn't take up data for NULL values, making it better suited for storing sparse data. Create separate "row" and "column" tables, as well as an intermediate table to link them and store the value for the column at that row. I believe this is the more traditional RDMS solution, but there's more complexity and overhead associated with it. I also found PostgreDynamic, which claims to better support sparse data, but I don't want to switch my entire database server to a PG fork just for this feature. Are there any other solutions? Which one should I use?

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• Help to choose NoSQL database for project

  - by potapuff

  There is a table: doc_id(integer)-value(integer) Approximate 100k doc_id and 27?? rows. Majority query on this table - searching documents similar to current document: select 10 documents with maximum of (count common to current document value)/(count ov values in document). Nowadays we use PostgreSQL. Table weight (with index) ~1,5 GB. Average query time ~0.5s. Should I transfer all this to NoSQL base, if so, what?

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