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  • Scalability comparison between different DBMSs

    - by Björn Lindfors
    By what factor does the performance (read queries/sec) increase when a machine is added to a cluster of machines running either: a Bigtable-like database MySQL? Google's research paper on Bigtable suggests that "near-linear" scaling is achieved can be achieved with Bigtable. This page here featuring MySQL's marketing jargon suggests that MySQL is capable of scaling linearly. Where is the truth?

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  • How to create a "facade" table?

    - by tputkonen
    A legacy database contains a join table which links tables table1 and table2, and contains just two foreign keys: TABLE_ORIG: table1_id table2_id In order to utilize this table using JPA I would need to create a surrogate primary key to the link table. However, the existing table must not be modified at all. I would like to create another table which would contain also a primary key in addition to the foreign keys: TABLE_NEW: id table1_id table2_id All changes to TABLE_ORIG should be reflected in TABLE_NEW, and vice versa. Is this doable in mysql?

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  • mysql query - blog posts and comments with limit

    - by Lemon
    Hi, I have 2 tables: comments and posts and I'd like to display a list of 15 posts and maximum 2 most recent comments under each blog post the database scheme looks like this posts_table: post_id, post_txt, post_timestamp comments_table: post_id, comment_txt, comment_timestamp how the mysql query should look like to select 15 posts and related comments (max 2 most recent ones per post) ??? thanks, Leo

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  • google app engine persistent globals

    - by Joey
    Hi, I'm looking for a way to keep the equivalent of persistent global variables in app engine (python). What I'm doing is creating a global kind that I initialize once (i.e. when I reset all my database objects when I'm testing). I have things in there like global counters, or the next id to assign certain kinds I create. Is this a decent way to do this sort of thing or is there generally another approach that is used?

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  • how to compare dates in php and sql?

    - by sebastian
    Hi, I want to make a notification system. Shortly.. to compare two dates, the only problem is that i want to compare the months. to see if a month or two have passed from last notification. i want to use one or two months from an entry in a mysql database. the client must select when the notification must come, one or two months. thank you, Sebastian

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  • Function that creates a timestamp in c#

    - by Konstantinos
    Hi there, I was wondering, is there a way to create a timestamp in c# from a datetime? I need a millisecond precision value that also works in Compact Framework(saying that since DateTime.ToBinary() does not exist in CF). My problem is that i want to store this value in a database agnostic way so i can sortby it later and find out which value is greater from another etc.

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  • SQLite join selection from the same table using reference from another table

    - by daikini
    I have two tables: table: points |key_id | name | x | y | ------------------------ |1 | A |10 |20 | |2 | A_1 |11 |21 | |3 | B |30 |40 | |4 | B_1 |31 |42 | table: pairs |f_key_p1 | f_key_p2 | ---------------------- |1 | 2 | |3 | 4 | Table 'pairs' defines which rows in table 'points' should be paired. How can I query database to select paired rows? My desired query result would be like this: |name_1|x_1|x_2|name_2|x_2|y_2| ------------------------------- |A |10 |20 |A_1 |11 |21 | |B |30 |40 |B_1 |31 |41 |

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  • Why empty String is treated as null in oracle?

    - by GK
    We are using empty string in DB2 database for some business logic. but when the same record tried to insert into the Oracle it throws some not null property references to null value error. that is oracle treats empty string as null. So i am wondering why it is like that. and if there is a requirement of storing empty string how to do that on oracle?

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  • do's and don'ts for writing mysql queries

    - by nik
    One thing I always wonder while writing query is that am I writing most optimized query or not? I know certain things like: 1) using SELECT field1, filed2 instead of SELECT * 2) Giving proper indexes to the tables but I am sure there are more things that should be kept in mind for writing queries, since most of the database can only grow more and optimal query will help gr8 in execution time, Can u share some tips and tricks on writing queries?

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  • Databases Views with Parameters

    - by asrijaal
    Hi there, I know that is it possible to create a View with Parameters at MSSQL, does anyone knows if I can achieve something similar with a DB2 database? I have a more complicated query which includes a user number which I want to pass as param to the view.

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  • ORA-01438: value larger than specified precision allows for this column

    - by bobir
    We get sometimes the following error from our partner's database: ORA-01438: value larger than specified precision allows for this column The full response looks like the following: ORA-01438: value larger than specified precision allows for this column ORA-06512: at "UMAIN.PAY_NET_V1_PKG", line 176 ORA-06512: at line 1 5592988 What can be the cause for this error? Thank you in advance.

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  • SQLite connection pooling with Fluent NHibernate

    - by Groo
    Is there a way to setup SQLite connection pooling using Fluent NHibernate configuration? E.g. equivalent of DataSource=:memory: would be: var sessionFactory = Fluently .Configure() .Database(SQLiteConfiguration.Standard.InMemory) (etc.) Is there something eqivalent to "Pooling=True;Max Pool Size=1;"?

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  • Error: The conversion of a nvarchar data type to a datetime data type resulted in an out-of-range value

    - by CPM
    I know that there are simmilar questions like this on the forum, however I am still having problems to update a datetime field o the database. I dont get any problems when inserting but I get problems when updating and I am formating the same way , like this: e.Values.Item("SelectionStartDate") = Format(startdate, "yyyy-MM-dd") + " " + startTime1 + ".000" startTime is of type string. I have tried different solution that I came across on the internet but still get this error. Please help. Thanks in advance

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  • Check if access table exists

    - by HasanGursoy
    I want to log web site visits' IP, datetime, client and refferer data to access database but I'm planning to log every days log data in separate tables in example logs for 06.06.2010 will be logged in 2010_06_06 named table. When date is changed I'll create a table named 2010_06_07. But the problem is if this table is already created. Any suggestions how to check if table exists in Access?

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  • Cassandra or MySQL/PostgreSQL?

    - by Ivri
    Hi! I have huge database (kinda wordnet). And want to know if it's easier to use Cassandra instead of MySQL|PostrgreSQL All my life I was using MySQL and PostrgreSQL and I could easily think in terms of relational algebra, but several weeks ago I learned about cassandra and that it's used in facebook and twitter. Is it more convenient? What DBMS are usually used nowadays to store social net's data, relationships between objects, wordnet?

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  • Fast way to code forms in C# which is bind to SQL data

    - by adopilot
    I am coming from MS-ACESS world and their programing habits, There was nice utility to make form from table, You can simply hit right click on table and make form for it. Now I looking for something similar for Visual Studio and WinForms. I am trying to develop simple application for which I need to have more then 30 forms for handling data, till now I designed database tables, keys and sprocs in SQL2008 and before I start coding forms for handling data, I asking You for main guidelines how to save my time while coding forms.

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  • Round date to fiscal year

    - by Dave Jarvis
    The following database view rounds the date back to the closest fiscal year (April 1st): CREATE OR REPLACE VIEW FISCAL_YEAR_VW AS SELECT CASE WHEN to_number(to_char( SYSDATE, 'MM' )) < 4 THEN to_date('1-APR-'||to_char(add_months(SYSDATE, -12), 'YYYY'), 'dd-MON-yyyy') ELSE to_date('1-APR-'||to_char(SYSDATE, 'YYYY'), 'dd-MON-yyyy') END AS fiscal_year FROM dual; This allows us to calculate the current fiscal year based on today's date. How can this calculation be simplified or optimized?

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  • mysql query for getting all messages that belong to user's contacts

    - by aharon
    So I have a database that is setup sort of like this (simplified, and in terms of the tables, all are InnoDBs): Users: contains based user authentication information (uid, username, encrypted password, et cetera) Contacts: contains two rows per relationship that exists between users as (uid1, uid2), (uid2, uid1) to allow for a good 1:1 relationship (must be mutual) between users Messages: has messages that consist of a blob, owner-id, message-id (auto_increment) So my question is, what's the best MySQL query to get all messages that belong to all the contacts of a specific user? Is there an efficient way to do this?

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  • Replacing ORM schema without dropping the entire data

    - by Udi
    Hey, I'm using OpenJPA as a JPA provider. Is there a way in which I can recreate the database tables (When an entity changes) without dropping the entire data? When an entity changes, I drop and create every table in the store, and obviously lose the data within. Is there a tool or product to keep the data somehow? Thanks, Udi

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