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  • Database design

    - by Hadad
    Hello, I've a system, that have two types of users (Companies and individuals).all types have a shared set of properties but they differ in another. What is the best design merge all in one table that allows null for unmatched properties, or separate them in two tables related to a basic table with a one to one relationship. Thanks.

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  • Database Optimization techniques for amateurs.

    - by Zombies
    Can we get a list of basic optimization techniques going (anything from modeling to querying, creating indexes, views to query optimization). It would be nice to have a list of these, one technique per answer. As a hobbyist I would find this to be very useful, thanks. And for the sake of not being too vague, let's say we are using a maintstream DB such as MySQL or Oracle, and that the DB will contain 500,000-1m or so records across ~10 tables, some with foreign key contraints, all using the most typical storage engines (eg: InnoDB for MySQL). And of course, the basics such as PKs are defined as well as FK contraints.

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  • Optimize SQL query (Facebook-like application)

    - by fabriciols
    My application is similar to Facebook, and I'm trying to optimize the query that get user records. The user records are that he as src ou dst. The src is in usermuralentry directly, the dst list are in usermuralentry_user. So, a entry can have one src and many dst. I have those tables: mysql> desc usermuralentry ; +-----------------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------+------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | user_src_id | int(11) | NO | MUL | NULL | | | private | tinyint(1) | NO | | NULL | | | content | longtext | NO | | NULL | | | date | datetime | NO | | NULL | | | last_update | datetime | NO | | NULL | | +-----------------+------------------+------+-----+---------+----------------+ 10 rows in set (0.10 sec) mysql> desc usermuralentry_user ; +-------------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | usermuralentry_id | int(11) | NO | MUL | NULL | | | userinfo_id | int(11) | NO | MUL | NULL | | +-------------------+---------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) And the following query to retrieve information from two users. mysql> explain SELECT * FROM usermuralentry AS a , usermuralentry_user AS b WHERE a.user_src_id IN ( 1, 2 ) OR ( a.id = b.usermuralentry_id AND b.userinfo_id IN ( 1, 2 ) ); +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | 1 | SIMPLE | b | ALL | usermuralentry_id,usermuralentry_user_bcd7114e,usermuralentry_user_6b192ca7 | NULL | NULL | NULL | 147188 | | | 1 | SIMPLE | a | ALL | PRIMARY | NULL | NULL | NULL | 1371289 | Range checked for each record (index map: 0x1) | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ 2 rows in set (0.00 sec) but it is taking A LOT of time... Some tips to optimize? Can the table schema be better in my application?

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  • Why is it possible to enumerate a LinqToSql query after calling Dispose() on the DataContext?

    - by DanM
    I'm using the Repository Pattern with some LinqToSql objects. My repository objects all implement IDisposable, and the Dispose() method does only thing--calls Dispose() on the DataContext. Whenever I use a repository, I wrap it in a using person, like this: public IEnumerable<Person> SelectPersons() { using (var repository = _repositorySource.GetNew<Person>(dc => dc.Person)) { return repository.GetAll(); } } This method returns an IEnumerable<Person>, so if my understanding is correct, no querying of the database actually takes place until Enumerable<Person> is traversed (e.g., by converting it to a list or array or by using it in a foreach loop), as in this example: var persons = gateway.SelectPersons(); // Dispose() is fired here var personViewModels = ( from b in persons select new PersonViewModel { Id = b.Id, Name = b.Name, Age = b.Age, OrdersCount = b.Order.Count() }).ToList(); // executes queries In this example, Dispose() gets called immediately after setting persons, which is an IEnumerable<Person>, and that's the only time it gets called. So, a couple questions: How does this work? How can a disposed DataContext still query the database for results when I walk the IEnumerable<Person>? What does Dispose() actually do? I've heard that it is not necessary (e.g., see this question) to dispose of a DataContext, but my impression was that it's not a bad idea. Is there any reason not to dispose of it?

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  • Getting records from a table based on a filter field and Between but also having the OR login for mu

    - by Pentium10
    I have a this table, where I store multiple ids and an age range (def1,def2) CREATE TABLE "template_requirements" ("_id" INTEGER NOT NULL, "templateid" INTEGER, "def1" VARCHAR(255), "def2" VARCHAR(255), PRIMARY KEY("_id")) Having values such as: templateid | def1 | def2 100 | 7 | 25 200 | 40 | 90 300 | 7 | 25 300 | 40 | 60 as you see for templateid 300 we have an or logic: age between 7 and 25 or age between 40 and 60. I want to get all the template ids that are not for a certain age like 25... What's the problem? If I run a query like this one: SELECT group_concat(templateid) FROM template_requirements where and '25' not between cast(def1 as integer) and cast(def2 as integer) it returns 200, 300, which is wrong, as the 300 matched on row 40 to 60, but shouldn't be included in the result as we have a condition with same templateid 7 to 25 that fails the not beetween stuff. How would be the correct query in SQLite, I would like to keep the group_concat stuff.

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  • Database table schema design - varchar(n). Suitable choice of N

    - by morpheous
    Coming from a C background, I may be getting too anal about this and worrying unnecessarily about bits and bytes here. Still, I cant help thinking how the data is actually stored and that if I choose an N which is easily factorizable into a power of 2, the database will be more effecient in how it packs data etc. Using this "logic", I have a string field in a table which is a variable length up to 21 chars. I am tempted to use 32 instead of 21, for the reason given above - however now I am thinking that I am wasting disk space because there will be space allocated for 11 extra chars that are guaranteed to be never used. Since I envisage storing several tens of thousands of rows a day, it all adds up. Question: Mindful of all of the above, Should I declare varchar(21) or varchar(32) and why?

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  • Multiple ID's in database

    - by eric
    I have a database that contains a few tables such as person, staff, member, and supporter. The person table contains information about every staff, member, and supporter. The information it contains is name,address,email, and telephone. I also created an id that is the primary key. My issue is that I also have an primary key ID for staff, member, and supporter. For instance, in the person table is John with id 1. He is a supporter so in the supporter table is pID(for person id)to reference back to John with all his information and ID(for supporter ID). pID references to the person table and every person has an ID incremented by 1 starting at 1. supporter ID is for every supporter and also starts at 1 and is incremented by 1. Is it possible to have in the supporter table pID = 1 and supporter ID = 1? Another person may have a pID = 26 and supporter ID = 5. Or will supporter ID have to be different than the pID and be something like "sup"? So you would have pID = 1 and supporter ID = sup1 or pID = 26 and supporter ID = sup5

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  • what is the 'extra' mean in this django code..

    - by zjm1126
    TOPIC_COUNT_SQL = """ SELECT COUNT(*) FROM topics_topic WHERE topics_topic.object_id = maps_map.id AND topics_topic.content_type_id = %s """ MEMBER_COUNT_SQL = """ SELECT COUNT(*) FROM maps_map_members WHERE maps_map_members.map_id = maps_map.id """ maps = maps.extra(select=SortedDict([ ('member_count', MEMBER_COUNT_SQL), ('topic_count', TOPIC_COUNT_SQL), ]), select_params=(content_type.id,)) i don't know this mean, thanks

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  • How to group by having the same id?

    - by simpatico
    Hello, I want the customerid who bought product X and Y and Z, from the following schema: Sales(customerid, productName, rid); I could do the intersection: select customerid from sales where productName='X' INTERSECT select customerid from sales where productName='X' INTERSTECT select customerid from sales where productName='Z' Is this the best I could do?

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  • IS NULL vs = NULL in where clause + MSSQL

    - by Nev_Rahd
    Hello How to check a value IS NULL [or] = @param (where @param is null) Ex: Select column1 from Table1 where column2 IS NULL = works fine If I want to replace comparing value (IS NULL) with @param. How can this be done Select column1 from Table1 where column2 = @param = this works fine until @param got some value in it and if is null never finds a record. How can this achieve?

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  • select distinct over specific columns

    - by Midhat
    A query in a system I maintain returns QID AID DATA 1 2 x 1 2 y 5 6 t As per a new requirement, I do not want the (QID, AID)=(1,2) pair to be repeated. We also dont care what value is selected from "data" column. either x or y will do. What I have done is to enclose the original query like this SELECT * FROM (<original query text>) Results group by QID,AID Is there a better way to go about this? The original query uses multiple joins and unions and what not, So I would prefer not to touch it unless its absolutely necesary

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  • Does UNIQ constraint mean also an index on that field(s)?

    - by Gremo
    As title, should i defined a separate index on email column (for searching purposes) or the index is "automatically" added along with UNIQ_EMAIL_USER constraint? CREATE TABLE IF NOT EXISTS `customer` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL, `first` varchar(255) NOT NULL, `last` varchar(255) NOT NULL, `slug` varchar(255) NOT NULL, `email` varchar(255) NOT NULL, `created_at` datetime NOT NULL, `updated_at` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `UNIQ_SLUG` (`slug`), UNIQUE KEY `UNIQ_EMAIL_USER` (`email`,`user_id`), KEY `IDX_USER` (`user_id`) ) ENGINE=InnoDB;

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  • How to repair "order by" after union of 2 selects from 1 tables

    - by 4e4el
    I have a dropDownList on my form, where i need to have union of values from 2 colums of table [ost]. Type of this columns is currency. I have russian version of access, default value of curency in "rur" and i need "uah". I need to change format and save "order by". I use this query: (SELECT distinct FORMAT([Sum1] ,'# ##0.00" uah.";-# ##0.00" uah."') FROM ost) Union (SELECT distinct FORMAT([Sum2],'# ##0.00" uah.";-# ##0.00" uah."') FROM ost) ORDER BY 1

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  • Redundancy in doing sum()

    - by Abhi
    table1 - id, time_stamp, value This table consists of 10 id's. Each id would be having a value for each hour in a day. So for 1 day, there would be 240 records in this table. table2 - id Table2 consists of a dynamically changing subset of id's present in table1. At a particular instance, the intention is to get sum(value) from table1, considering id's only in table2, grouping by each hour in that day, giving the summarized values a rank and repeating this each day. the query is at this stage: select time_stamp, sum(value), rank() over (partition by trunc(time_stamp) order by sum(value) desc) rn from table1 where exists (select t2.id from table2 t2 where id=t2.id) and time_stamp >= to_date('05/04/2010 00','dd/mm/yyyy hh24') and time_stamp <= to_date('25/04/2010 23','dd/mm/yyyy hh24') group by time_stamp order by time_stamp asc If the query is correct, can this be made more efficient, considering that, table1 will actually consist of thousand's of id's instead of 10 ? EDIT: I am using sum(value) 2 times in the query, which I am not able to get a workaround such that the sum() is done only once. Pls help on this

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  • Select where a value present

    - by Roy
    First a database example: id, product_id, cat, name, value -------------------------------- 1,1,Algemeen,Processor,2 Ghz 2,1,Algemeen,Geheugen,4 GB 3,2,Algemeen,Processor,3 Ghz 4,2,Algemeen,Geheugen,4 GB 5,3,Beeldscherm,Inch,22" 6,3,Beeldscherm,Kleur,Zwart 7,3,Algemeen,Geheugen,3 GB 8,3,Algemeen,Processor,3 Ghz I want with one query to select the follow id's: 1,2,3,4,7,8 Because the cat = algemeen and the name = processor by these products. ID 5,6 are only present by product 3. So, the entry's (cat and name) which are present by all products (product_id) have to be selected. The database contains 80.000 entry's with a lot of diffrent cat's, name's and value's. Is this possible with one query or is some php necessary? How do I do this? My apologies for the bad English.

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  • How can I treat a sequence value like a generated key?

    - by Jeff Knecht
    Here is my situation and my constraints: I am using Java 5, JDBC, and DB2 9.5 My database table contains a BIGINT value which represents the primary key. For various reasons that are too complicated to go into here, the way I insert records into the table is by executing an insert against a VIEW; an INSTEAD OF trigger retrieves the NEXT_VAL from a SEQUENCE and performs the INSERT into the target table. I can change the triggers, but I cannot change the underlying table or the general approach of inserting through the view. I want to retrieve the sequence value from JDBC as if it were a generated key. Question: How can I get access to the value pulled from the SEQUENCE. Is there some message I can fire within DB2 to float this sequence value back to the JDBC driver?

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  • One on One table relation - is it harmful to keep relation in both tables?

    - by EBAGHAKI
    I have 2 tables that their rows have one on one relation.. For you to understand the situation, suppose there is one table with user informations and there is another table that contains a very specific informations and each user can only link to one these specific kind of informations ( suppose second table as characters ) And that character can only assign to the user who grabs it, Is it against the rules of designing clean databases to hold the relation key in both tables? User Table: user_id, name, age, character_id Character Table: character_id, shape, user_id I have to do it for performance, how do you think about it?

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  • copy an identity column into another table

    - by slake
    I have 2 tables that are related,both have identity columns for primary keys and i am using a vb form to insert data into them,My problem is that i cannot get the child table to get the primary key of the parent table and use this as its foreign key in my database. the data is inserted fine though no foreign key constraint is made.I am wondering if a trigger will do it and if so how. All my inserting of data is done in vb. The user wont insert any keys. all these are identity columns that are auto generated. If a trigger is my way out please illustrate with an example. If there is another way i can do this in VB itself then please advise and an example will be greatly appreciated Thanks in advance

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  • Embedded Java Databases for Large Data Sets

    - by ExAmerican
    I would like to port a PHP/MySQL-based client/server application to be a standalone desktop application written in Java. The database has grown to be fairly large, with several tables with hundreds of thousands of rows. I expect these could grow to over a million entries for certain tables. What embedded database would best handle this? HSQLDB and Sqlite seem to be the obvious choices, though I'm guessing there are others out there as well. My main priorities are the ability to perform queries on large amounts of data efficiently (this thread seems to confirm Sqlite can handle this) and the ease with which I can import old data from MySQL (I remember HSQLDB being kind of a pain for that). Note: I am aware that similar questions comparing embedded databases have been posted before (for example here and here) but as my priorities differ somewhat from most applications considering the large data migration I thought it justified a new question.

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  • Desgining a database with flexible user profile

    - by Mughrabi
    Hi, Am working on a design where I can have flexible attributes for a user & am confused how to continue the design of the schema. I made a table where I kept system needed information called users id username password Now, I wish to create a profile table and have one to one relation where all the other attributes in profile table such as email, first name, last name..etc. My question is, is there a way to add a third table in which even profile will be flexible if my clients need to create a new attribute he/she won't need any customization to the code? Regards,

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