sql and relational databases

-- Delete Table----------------------------------------------------------------------------------To add a constraint:ALTER TABLE Table name ADD CONSTRAINT constraint name constraint type specific constraint description1. The naming rules for constraint names are recommended in the form of constraint type _ constraint name.----------------------------------------------------------------------------------To delete a constraint:There are two ways to add a constraint to a specified tabl

relational databases Follow acid rulesTransactions are transaction in English, similar to real-world transactions, and have the following four features:1, A (atomicity) atomicityAtomicity is easy to understand, that is, all operations in a transaction are either done or not, and the transaction succeeds because all operations in the transaction are successful, and as long as one operation fails, the entire

intent lock is compatible with other locks that are lower than it. Batch update lock Batch update locks on a table allow multiple batches to load threads, load data into tables, and disallow other types of data access. Batch update locks are issued when table locking is enabled on a table, or when the table lock option is selected with a batch operation. Key Range Lock When using serializable isolation levels, key-range locks protect a range of rows that are implied in the result set and are no

Michael Kopp has more than 10 years of architecture and development experience in C ++ and Java/Jee. He is now a compuware technology strategist who specializes in the architecture and performance of large-scale product deployment. The following is a translation: Traditional enterprise database vendors often propose that nosql lacks professional monitoring and management tools. Their arguments are: enterprise applicationsProgramThe database needs to be fine-tuned and monitored to ensure stab

This article is translated from Coding-geek article: How does a relational the database work.Original link: http://coding-geek.com/how-databases-work/#Buffer-replacement_strategiesThis article translates the following chapters: One, Array, Tree and Hash tableThrough the previous chapters, we have already understood the concept of time complexity and merge ordering, and I will introduce three data stru

General purpose of converting a relational database into an XML fileProgram Always copy from others on the network Source code Today, I also posted my source code today. I believe this program will help you frequently extract data from the database and convert it into an XML file in your daily work. Recently, one thing in the company's project is to read data from the database table and convert it into an XML file for the client to download. Be

Relational databases use keys to construct relationships between data. Too many indirect relationships lead to complicated logic. Today, I encountered this situation when designing a public opinion monitoring system. For data output flexibility, the database is designed centered on customers and keywords. However, in order to increase the Cluster load, data crawling is designed to be distributed, which cr

operation can be combined into an SQL statement. Take a look at the revised code: $model = new Model (); $result = mysql_query ("UPDATE goods SET quantity = quantity-1 WHERE id = 1"); Because the relational database is stored in a file, modifications to the same record cannot be made concurrently. This means that even if A and B users buy at the same time, the inventory changes are in order, so the inve

The construction of the database must follow certain rules. In a relational database, this rule is a paradigm. A paradigm is a collection of relational patterns that conform to a certain level. Relationships in relational databases must meet certain requirements, that is, to satisfy different paradigms. There are six t

operations, so very slow, and the associated query is also very complex, resulting in low efficiency, often query business does not go index, query speed is very slow, mainly because of the complexity of the performance of the lower Summary Choosing a nosql requires the following 2 prerequisites:1. No acid required2. No correlation query required If you need the above two functions, you cannot select NoSQL Here are the full criteria for choosing a nosql:1 table structure is not fixed "because t

administrator. The use command is then used to switch to the target database, and the Db.createuser () command is used to create the user with the role name "ReadWrite".There are two types of common database user roles, read and ReadWrite. As the name implies, the former can only read data cannot be modified, the latter may read and modify.Here is an example:> Use testSwitched to DB test> Db.createuser ({User: "TestUser", pwd: "Testpass", roles:["ReadWrite"]})Successfully added User: {"user": "

performance of the system and various database management operations, including the followingComputing performance of--oracle database--Performance of database access operations--performance of backup and operation4. Create and open a databaseUsing DBCA5. Backing Up the databaseManufacturers have integrated, but need seamless backup recovery must be optimized for processing6. Registering Database UsersCreate users, assign permissions and roles7. Implementing Database DesignCreate table spaces t

characteristics are suitable for use with serialization isolation (serializable isolation):1, the data volume is large, but the transaction is short, only will update the database with less data rows2, two concurrent transactions the probability of modifying the same data is small3. A transaction with a relatively long run time only performs read-only operationsThis paragraph I see not quite understand, one is the transaction level of the read consistency, one is the sentence level of read cons

Transferred from: Http://blog.163.com/[email protected]/blog/static/285720652010950825538/6. Understanding SQL from a relational perspective6.1. Relationships and TablesAs we all know, the database we use today is usually a relational database. The relationship naturally lies in its critical position. Beginners of the database principle may be confused about the

data.Use the database engine to control access and quickly process transactions to meet the demanding needs of the enterprise and the need to process large amounts of data.Use the database engine to create a relational database for online transaction processing or online analytics processing data.This includes creating tables for storing data and database objects such as indexes, views, and stored procedures that are used to view, manage, and secure

Part i:relational Databases and SQLChapter2, ensuring Your Database Structureis sound.Database Design GuidelinesWhat is a relational databaseRDBMS (A relational database management systems) relational databaseTablesTables is the mainstructures in the database. Each table always represents aSingle, Specificsubject.Field

Label:Objective On a relational database commonly used SQL statement syntax is mainly relational database general structure, this paper discusses the relational database query SQL syntax. Grammar Review SELECT [ALL|DISTINCT] The order

Absrtact: With the development of application field and multimedia technology, people find many limitations and shortages of relational database, so database technology has entered the era of "post-relational database". The file database was born. In this paper, the similarities and differences of file database and relational database are compared from three aspe

We recommend that you read and understand the following articles: ◆ Use a partition in a Microsoft SQL Server 2000 data warehouse-http://msdn.microsoft.com/library/default.asp? URL =/library/techart/PartitionsInDW.htm◆ SQL Server 2000 step by step batch import case study-http://www.microsoft.com/technet/prodtechnol/ SQL /2000/maintain/incbulkload.mspx◆ Kimberly L

Initial Release1995 License Mechanism: Open Source SQL?: Yes Enterprises can use the open-source community version at the beginning, and then upgrade to the commercial version to run on Linux, Windows, OSX, FreeBSD, and Solaris to provide users with an intuitive graphic interface for designing databases. In view of its open-source community, mySQL has a lot of materials and tutorials for you to start and h