rdbms | 易学教程

Does MySQL/InnoDB implement true serializable isolation?

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问题 It is not entirely clear from MySQL documentation whether the InnoDB engine implements true serializable isolation 1 or snapshot isolation, which is often confusingly called "serializable" too. Which one is it? If MySQL InnoDB doesn't, are there any completely free, production-quality RDBMS which do? 1 where "true serializable isolation" means the absence of not only read anomalies as per the SQL standard, but also the write skew anomaly, explained in further detail here. 回答1: UPDATE: See

Check for changes to an SQL Server table?

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问题 How can I monitor an SQL Server database for changes to a table without using triggers or modifying the structure of the database in any way? My preferred programming environment is .NET and C#. I'd like to be able to support any SQL Server 2000 SP4 or newer. My application is a bolt-on data visualization for another company's product. Our customer base is in the thousands, so I don't want to have to put in requirements that we modify the third-party vendor's table at every installation. By

How does noSQL perform horizontal scaling and how it is more efficient than RDBMS scaling

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问题 I was reading about noSQL and relational DBMSs. After going through many posts, I am not able to find out exactly how noSQL systems perform horizontal scaling and how it is more efficient than RDBMS scaling. After all, RDBMSs also do replication and sharding. How this is fast in case of NoSql? 回答1: First of all, there is no technology or product called "NoSQL." NoSQL is a broad category describing dozens of different technologies, which each work differently. Please don't use the term "NoSQL"

How to store data with dynamic number of attributes in a database

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问题 I have a number of different objects with a varying number of attributes. Until now I have saved the data in XML files which easily allow for an ever changing number of attributes. But I am trying to move it to a database. What would be your preferred way to store this data? A few strategies I have identified so far: Having one single field named "attributes" in the object's table and store the data serialized or json'ed in there. Storing the data in two tables (objects, attributes) and using

TRIGGERs that cause INSERTs to fail? Possible?

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In cleaning up this answer I learnt a bit about TRIGGER s and stored procedures in MySQL, but was stunned that, while BEFORE INSERT and BEFORE UPDATE triggers could modify data, they seemingly couldn't cause the insert/update to fail (ie. validation). In this particular case I was able to get this to work by manipulating the data in such a way as to cause a primary key duplicate, which in this particular case made sense, but doesn't necessarily make sense in a general sense. Is this sort of functionality possible in MySQL? In any other RDBMS (my experience is limited to MySQL sadly)? Perhaps a

How universal is the LIMIT statement in SQL?

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问题 I'm in the process of generalizing a Django DB replication app and it uses the statement: SELECT %s FROM %s LIMIT 1 to fetch 1 row and use the Python DBAPI to describe the fields, it works fine with ORACLE and MySQL but, how cross platform is the LIMIT statement? 回答1: http://en.wikipedia.org/wiki/Select_(SQL)#Limiting_result_rows lists all of the major variants of the select command. I believe the best way to do this is to use the SET ROWCOUNT command before your SELECT statement. So, for you

Update specific field on SOLR index

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问题 I want to using solr for search on articles I have 3 table: Group (id , group name) ArticleBase (id, groupId, some other field) Article(id, articleBaseId, title, date, ...) in solr schema.xml file i just define all article field that mixed with ArticleBase table (for use one index on solr) like this: (id, articleBaseId, groupId, ...) problem : Admin want to change group (ArticleBase), therefore i must update (or replace) all indexed article in solr. right ? can i update groupId only in solr

Is this a good way to model address information in a relational database?

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问题 I'm wondering if this is a good design. I have a number of tables that require address information (e.g. street, post code/zip, country, fax, email). Sometimes the same address will be repeated multiple times. For example, an address may be stored against a supplier, and then on each purchase order sent to them. The supplier may then change their address and any subsequent purchase orders should have the new address. It's more complicated than this, but that's an example requirement. Option 1

Why NoSQL is better at “scaling out” than RDBMS?

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问题 I have read the following text in a technical blog discussing the advantages and disadvantages of NoSQL " For years, in order to improve performance on database servers, database administrators have had to buy bigger servers as the database load increases (scaling up) instead of distributing the database across multiple “hosts” as the load increases (scaling out). RDBMS do not typically scale out easily, but the newer NoSQL databases are actually designed to expand easily to take advantage of

When/Why to use Cascading in SQL Server?

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When setting up foreign keys in SQL Server, under what circumstances should you have it cascade on delete or update, and what is the reasoning behind it? This probably applies to other databases as well. I'm looking most of all for concrete examples of each scenario, preferably from someone who has used them successfully. Joel Coehoorn Summary of what I've seen so far: Some people don't like cascading at all. Cascade Delete Cascade Delete may make sense when the semantics of the relationship can involve an exclusive "is part of " description. For example, an OrderLine record is part of its