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  • How do you store sets in Cassandra?

    - by Ben W
    I'd like to convert this JSON to a data model in Cassandra, where each of the arrays is a set with no duplicates: var data = { "data1": { "100": [1, 2, 3], "200": [3, 4] }, "data2": { "k1", [1], "k2", [4, 5] } } I'd like to query like this: data["data1"]["100"] to retrieve the sets. Anyone know how you might model this in Cassandra? (The only thing I came up with was columns whose name was a set value and the value of the column was an empty string, but that felt wrong.) It's not OK to serialize the sets as JSON or some other string, which would make this much easier. Also, I should note that it's OK to split data1 and data2 into separate ColumnFamilies, it's not necessary that they're keys in the same one.

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  • Using "CASE" in Where clause to choose various column harm the performance

    - by zivgabo
    I have query which needs to be dynamic on some of the columns, meaning I get a parameter and according its value I decide which column to fetch in my Where clause. I've implemented this request using "CASE" expression: (CASE @isArrivalTime WHEN 1 THEN ArrivalTime ELSE PickedupTime END) >= DATEADD(mi, -@TZOffsetInMins, @sTime) AND (CASE @isArrivalTime WHEN 1 THEN ArrivalTime ELSE PickedupTime END) < DATEADD(mi, -@TZOffsetInMins, @fTime) If @isArrivalTime = 1 then chose ArrivalTime column else chose PickedupTime column. I have a clustered index on ArrivalTime and nonclustered index on PickedupTime. I've noticed that when I'm using this query (with @isArrivalTime = 1), my performance is a lot worse comparing to only using ArrivalTime. Maybe the query optimizer can't use\choose the index properly in this way? I compared the execution plans an noticed that when I'm using the CASE 32% of the time is being wasted on the index scan, but when I didn't use the CASE(just usedArrivalTime`) only 3% were wasted on this index scan. Anyone know the reason for this?

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  • Iterating dictionary indexes in django templates

    - by unclaimedbaggage
    Hi folks...I have a dictionary with embedded objects, which looks something like this: notes = { 2009: [<Note: Test note>, <Note: Another test note>], 2010: [<Note: Third test note>, <Note: Fourth test note>], } I'm trying to access each of the note objects inside a django template, and having a helluva time navigating to them. In short, I'm not sure how to extract by index in django templating. Current template code is: <h3>Notes</h3> {% for year in notes %} {{ year }} # Works fine {% for note in notes.year %} {{ note }} # Returns blank {% endfor %} {% endfor %} If I replace {% for note in notes.year %} with {% for note in notes.2010 %} things work fine, but I need that '2010' to be dynamic. Any suggestions much appreciated.

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  • SQL indexes for "not equal" searches

    - by bortzmeyer
    The SQL index allows to find quickly a string which matches my query. Now, I have to search in a big table the strings which do not match. Of course, the normal index does not help and I have to do a slow sequential scan: essais=> \d phone_idx Index "public.phone_idx" Column | Type --------+------ phone | text btree, for table "public.phonespersons" essais=> EXPLAIN SELECT person FROM PhonesPersons WHERE phone = '+33 1234567'; QUERY PLAN ------------------------------------------------------------------------------- Index Scan using phone_idx on phonespersons (cost=0.00..8.41 rows=1 width=4) Index Cond: (phone = '+33 1234567'::text) (2 rows) essais=> EXPLAIN SELECT person FROM PhonesPersons WHERE phone != '+33 1234567'; QUERY PLAN ---------------------------------------------------------------------- Seq Scan on phonespersons (cost=0.00..18621.00 rows=999999 width=4) Filter: (phone <> '+33 1234567'::text) (2 rows) I understand (see Mark Byers' very good explanations) that PostgreSQL can decide not to use an index when it sees that a sequential scan would be faster (for instance if almost all the tuples match). But, here, "not equal" searches are really slower. Any way to make these "is not equal to" searches faster? Here is another example, to address Mark Byers' excellent remarks. The index is used for the '=' query (which returns the vast majority of tuples) but not for the '!=' query: essais=> EXPLAIN ANALYZE SELECT person FROM EmailsPersons WHERE tld(email) = 'fr'; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------ Index Scan using tld_idx on emailspersons (cost=0.25..4010.79 rows=97033 width=4) (actual time=0.137..261.123 rows=97110 loops=1) Index Cond: (tld(email) = 'fr'::text) Total runtime: 444.800 ms (3 rows) essais=> EXPLAIN ANALYZE SELECT person FROM EmailsPersons WHERE tld(email) != 'fr'; QUERY PLAN -------------------------------------------------------------------------------------------------------------------- Seq Scan on emailspersons (cost=0.00..27129.00 rows=2967 width=4) (actual time=1.004..1031.224 rows=2890 loops=1) Filter: (tld(email) <> 'fr'::text) Total runtime: 1037.278 ms (3 rows) DBMS is PostgreSQL 8.3 (but I can upgrade to 8.4).

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  • How to use Unique Composite Key

    - by LifeH2O
    I have a table Item(ItemName*, ItemSize*, Price, Notes) I was making composite key of (ItemName,ItemSize) to uniquely identify item. And now after reading some answers on stackoverflow suggesting the use of UNIQUE i revised it as Item(ItemID*, ItemName, ItemSize, Price, Notes) But How to apply UNIQUE constraint on ItemName and ItemSize please correct if there is something wrong in question

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  • which is better, creating a materialized view or a new table?

    - by Carson
    I have some demanding mysql queries that are needed to grap same up-to-date datasets from 5-7 mysql tables. I am thinking of creating a table or materialized view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create materialized view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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  • What are some useful SQL statements / usage patterns that should be known by all developers who may

    - by Jian Lin
    What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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  • Error(2,7): PLS-00428: an INTO clause is expected in this SELECT statement

    - by omgzor
    I'm trying to create this trigger and getting the following compiler errors: create or replace TRIGGER RESTAR_PLAZAS AFTER INSERT ON PLAN_VUELO BEGIN SELECT F.NRO_VUELO, M.CAPACIDAD, M.CAPACIDAD - COALESCE(( SELECT count(*) FROM PLAN_VUELO P WHERE P.NRO_VUELO = F.NRO_VUELO ), 0) as PLAZAS_DISPONIBLES FROM VUELO F INNER JOIN MODELO M ON M.ID = F.CODIGO_AVION; END RESTAR_PLAZAS; Error(2,7): PL/SQL: SQL Statement ignored Error(8,5): PL/SQL: ORA-00933: SQL command not properly ended Error(8,27): PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following: begin case declare end exception exit for goto if loop mod null pragma raise return select update while with <an identifier> <a double-quoted delimited-identifier> <a bind variable> << close current delete fetch lock insert open rollback savepoint set sql execute commit forall merge pipe Error(2,1): PLS-00428: an INTO clause is expected in this SELECT statement What's wrong with this trigger?

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  • DB Design to store custom fields for a table

    - by Fazal
    Hi All, this question came up based on the responses I got for the question http://stackoverflow.com/questions/2785033/getting-wierd-issue-with-to-number-function-in-oracle As everyone suggested that storing Numeric values in VARCHAR2 columns is not a good practice (which I totally agree with), I am wondering about a basic Design choice our team has made and whether there are better way to design. Problem Statement : We Have many tables where we want to give certain number of custom fields. The number of required custom fields is known, but what kind of attribute is mapped to the column is available to the user E.g. I am putting down a hypothetical scenario below Say you have a laptop which stores 50 attribute values for every laptop record. Each laptop attributes are created by the some admin who creates the laptop. A user created a laptop product lets say lap1 with attributes String, String, numeric, numeric, String Second user created laptop lap2 with attributes String,numeric,String,String,numeric Currently there data in our design gets persisted as following Laptop Table Id Name field1 field2 field3 field4 field5 1 lap1 lappy lappy 12 13 lappy 2 lap2 lappy2 13 lappy2 lapp2 12 This example kind of simulates our requirement and our design Now here if somebody is lookinup records for lap2 table doing a comparison on field2, We need to apply TO_NUMBER. select * from laptop where name='lap2' and TO_NUMBER(field2) < 15 TO_NUMBER fails in some cases when query plan decides to first apply to_number instead of the other filter. QUESTION Is this a valid design? What are the other alternative ways to solve this problem One of our team mates suggested creating tables on the fly for such cases. Is that a good idea How do popular ORM tools give custom fields or flex fields handling? I hope I was able to make sense in the question. Sorry for such a long text.. This causes us to use TO_NUMBER when queryio

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  • Duplicate ID/indexes and looping

    - by Justin Alexander
    I realize having two elements in the same html doc with the same ID is wrong, bad, immoral, and will lead to global warming. But... I'm trying to write an XSS widgit, so I really have no control over the quality of the parent web page. I loop through document.images to retrieve a list of images on the page. I perform an action on each one. for(img in document.images){ ... } i've also tried for(var i=0;i<document.images.length;i++){ ... } in both cases it allows me to loop through all of the elements, BUT when trying trying to reference an object with a duplicate ID, I always get the first (in order of the html). When using debugger in IE8 i'm able to see that both elements ARE listed, but that they both have the same index (in IE the index of the document.images is either sequential or matches the image ID) Does anyone have a better solution?

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  • Fastest way to perform subset test operation on a large collection of sets with same domain

    - by niktech
    Assume we have trillions of sets stored somewhere. The domain for each of these sets is the same. It is also finite and discrete. So each set may be stored as a bit field (eg: 0000100111...) of a relatively short length (eg: 1024). That is, bit X in the bitfield indicates whether item X (of 1024 possible items) is included in the given set or not. Now, I want to devise a storage structure and an algorithm to efficiently answer the query: what sets in the data store have set Y as a subset. Set Y itself is not present in the data store and is specified at run time. Now the simplest way to solve this would be to AND the bitfield for set Y with bit fields of every set in the data store one by one, picking the ones whose AND result matches Y's bitfield. How can I speed this up? Is there a tree structure (index) or some smart algorithm that would allow me to perform this query without having to AND every stored set's bitfield? Are there databases that already support such operations on large collections of sets?

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  • My database has been deleted suddenly on the server how to recover it?

    - by user2728312
    I'm running an application on windows server that connect to a SQL Server database. Today, when I opened SQL Server Management Studio, I was surprised the database is not in the list of the databases! I don't know what's the reason. I searched in the server files but I can't find the database and also in the recycle bin. I put my database in C:\db\myWeb.mdf and suddenly it's been removed! Can anyone tell me how to recover the database?

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  • SQL Server (2008) Creating link tables with unique rows

    - by peteski22
    Hi guys, I'm having trouble getting in touch with SQL Server Managemen Studio 2008! I want to create a link-table that will link an Event to many Audiences (EventAudience). An example of the data that could be contained: EventId | AudienceId 4 1 5 1 4 2 However, I don't want this: EventId | AudienceId 4 1 4 1 I've been looking at relationships and constraints.. but no joy so far! As a sneaky second part to the question, I would like to set up the Audience table such that if a row is deleted from Audience, it will clear down the EventAudience link table in a cascading manner. As always, ANY help/advice appreciated! Thanks Pete

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  • How to create schema that have an access as that of dbo and can be accessed by sa user

    - by Shantanu Gupta
    I am new to schema, roles and user management part in sql server. Till now I used to work with simple dbo schema but now after reading few articles I am intrested in creating schema for managing my tables in a folder fashion. At present, I want to create a schema where i want to keep my tables that have same kind of functionality. When I tries to create a schema then I faces a problem while using query, permissions etc. First of all i want to get used to of using schemas then only I want to explore it. But due to initial stages and work pressure as well i m not able to implement it yet. What can i do to start using schema with default permissions as that of dbo. Also let me know about creating roles and assigning roles on these schema. I want all this to be accessible by sa user itself at present. What is the concept behind all these things

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  • What would be the best schema to store the 'address' for different entities?

    - by Cesar
    Suppose we're making a system where we have to store the addrees for buildings, persons, cars, etc. The address 'format' should be something like: State (From a State list) County (From a County List) Street (free text, like '5th Avenue') Number (free text, like 'Chrysler Building, Floor 10, Office No. 10') (Yes I don't live in U.S.A) What would be the best way to store that info: Should I have a Person_Address, Car_Address, ... Or the address info should be in columns on each entity, Could we have just one address table and try to link each row to a different entity? Or are there another 'better' way to handle this type of scenario? How would yo do it?

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  • The good SQL database to process a lot of data?

    - by Dorian
    I have to process like 10-100 millions records. I have to give the data to the client when it's finish. The data is givent as SQL requests to execute in the database. He have a powerful server with MySQL, I think it will be fast enough. The issue is my computer is not as powerful as his server, so I would like to use an other SQL server who is compatible (I export his database and import it in my computer) with MySQL but more powerful. What should I use? Or am I doomed to use MySQL?

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  • SQL Server database synchronization issues

    - by George2
    Hello everyone, I have two SQL Server 2008 Enterprise databases (on two machines), and one of the databases is master database and another database is slave database (master database is read/write, slave database is readonly). I want to have daily update from master database to slave database (i.e. new data inserted/updated/deleted in master database could be synchronized to slave database daily or manually controlled). I only need to sync several tables of the databases, not all of the database. Any solutions or documents? thanks in advance, George

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  • boost multi_index partial indexes

    - by Gokul
    Hi, I want to implement inside boost multi-index two sets of keys with same search criteria but different eviction criteria. Say i have two sets of data with same search condition, but one set needs a MRU(Most Recently Used) list of 100 and the other set requires a MRU of 200. Say the entry is like this class Student { int student_no; char sex; std::string address; }; The search criteria is student_no, but for sex='m', we need MRU of 200 and for sex='f', we need a MRU of 100. Now i have a solution where in i introduce a new ordered index to maintain ordering. For example the IndexSpecifierList will be something like this typedef multi_index_container< Student, indexed_by< ordered_unique< member<Student, int, &Student::student_no> >, ordered_unique< composite_key< member<Student, char, &Student::sex>, member<Student, int, &Student::sex_specific_student_counter> > > > > student_set Now everytime, i am inserting a new one, i have to take a equal_range for that using index 2 and remove the oldest one and if something is getting re-used, i have to update it by incrementing the counter. Is there a better solution to this kind of problem? Thanks, Gokul.

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  • Relational databases are not suited for my application - what's the alternative?

    - by waitinforatrain
    Hi, I'm writing a CMS in PHP that allows the user to define different fields (e.g. a Blog page could have fields for Title (string), Content (rich text), Picture (file)). I need the user to be able to add and remove fields dynamically, and the only way I can think of to do it with relational DBs is to serialise all these values and store them in one cell. This seems like a slow approach and like I'm trying to fit something dynamic within a static structure. Could someone recommend anything that is PHP-compatible that would make this easier?

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