dcl sql

Second, the SQL languageSQL structure Query Language structured queries languageSQL statement: DDL statement DML statement, DCL statementDdl--data define language--create, alter, drop-data definition languageDml--data Management language--insert, UPDATE, delete--Data manipulation languageDcl--data Control Language--grant, revoke--Data Control languageIntroduction to 1.DDL Statements1.1 Creating a TableSql>

a number of time-consuming operations together to execute. 2.DML The database divides the SQL statements into three categories: DML statements, DDL statements, DCL statements The Database maintenance language (data manipulation Language or data modification LANGUAGE,DML) includes select,insert,update,delete statements, and the latter three are used to change the data in the table. DML statements are

DDL (data definition Language): Database definition language 　　1, create table table_name ()　　2, alert table table_name(1). Add columnsAn example of the complete definition of the ALTER table tb_name add column: Alter TABLE S_stu Add (sname varchar2 (), sage number);(2). Delete a columnAlter table tb_name drop column col_name;(3). Modifying column properties (data types and constraints)An example of the complete definition of the ALTER table tb_name modify column: ALTER TABLE S_STU modify sname

You can take a look at this Weibo blog: http://blog.csdn.net/jiben2qingshan/article/details/7832344http://blog.163.com/chenwenlin_89/blog/static/135159174201011295818330/The DDL (data definition Language) is used to manipulate the properties of objects and objects, including the database itself, as well as database objects, such as tables, views, and so on, and the DDL's management and definition of these objects and properties are represented in the Create, Drop and alter on. Special note: The

Lazysingleton () {} public static synchronized Lazysingleton getinstance () {if (instance = = nul L) {instance = new Lazysingleton (); } return instance; }} Pros: Do not perform getinstance pairs will not be instantiated disadvantage: The response is not fast when loading for the first time. Each call to getinstance The synchronization cost is large . (lots of unnecessary synchronizations)

Tags: style blog http color os using AR SP dataThis article mainly records some of the main MongoDB's DCL operations.MongoDB does not require a user name and password by default to log in with Mongodb.exeFirst, open the MONOGODB mode of accessModify the registration statement of the MongoDB service, modify the add--auth parameter, see the installation of MongoDB introduction" $MONGODB _home\bin\mongod.exe " " $MONGODB _home\mongo.cfg " --install --aut

Label:triggers cannot invoke or indirectly invoke a DCL statement such as Commit,rollback DDL statements and Commit,rollback statements cannot be run in triggers DDL statements: DDL statement terms define and manage objects in the database, such as Create,alter,drop,truncate, and DDL operations are implicitly committed!The operation takes effect immediately and the original data is not placed in the rollback segment and cannot be rolled back. Operatio

Transferred from: http://www.iteye.com/topic/875420 If you search the reason why the DCL in Java fails in the online analysis, will talk about the compiler will do optimization and so on, I believe you see this must feel very frustrated, very helpless, the process of their own writing is not confident. I understand this feeling because I've been there, and that's probably why people on the Internet have always liked to talk about

is thread security. However, volatile provides the opportunity to modify multiple threads. However, you can directly operate on the primary storage.Therefore, be sure to associate final with the thread. Instead of how to improve performance. Synchronized principle.Modifier:Synchronized (OBJ ){......}OBJ can be this, an attribute of the object.OBJ is also called Monitor.Note that synchronized has the same principle of modifying the block method. The default value of this is monitor.Generally,

DCL (understanding)* A project to create a user! A project corresponding to the database only one!* This user can only have access to this database, other databases you will not be able to operate!1. Create a user* CREATE user username @ip address identified by ' password ';> users can only log on to the specified IP address* CREATE user username @ '% ' identified by ' password ';> Users can log on at any IP address2. Authorization to the user* GRANT

DCL (Data Control Language) statement: A statement that controls the level of permission and access to different data segments directly. These statements define the database, table, field, user's access rights, and security level. The main statement keywords include GRANT, revoke, and so on.DCL statements are primarily used by DBAs to manage object permissions in the system, and are seldom used by general developers. Here is an example to illustrate b

DQL (data Query language) querying languageA query statement consisting primarily of selectBasic syntax: Select field name from table name where query conditionDML (Data manipulation language) manipulation languageMainly used to operate the database data, is our common use of additions and deletions to check. SELECT UPDATE INSERT DELETEDDL (data definition Language) database definition languageIt is primarily used for initializing tasks such as defining or altering the structure of tables, data

initialisers because(Spurious reason X)", But there is no" magic "place to put variable initialisation in cases such as this !) However it is created, the JVM ensures that this static initialisation code is called exactly once, when the class is first referred to and loaded. Using the class loader is generally my preferred way of dealing with lazy static initialisation. the code's nice and simple, and I don't think you can actually do it any more efficiently. the time that it won't work of cour

DCL: Data Control language, mainly create users, manage user rights Main keywords: Great Grant Revoke drop 1. Create user CREATE user username @ip address identified by password CREATE user username @ '% ' identified by password 2. Give user authorization GRANT permission 1,..., permission n on database. Table name to user name @ip address 3. Revoke permission REVOKE permission on database name. Table name from user name @ip address Note: A

Data Control Language (DCL) permissions in MySQLIn MySQL, permissions are some of the system's default "nouns" (words), about 30, each of which indicates "what work can be done." Assigning permissions is equivalent to what a user can do. The main permissions are as follows: user information from MySQL in MySQL is stored in the user table of the system database MySQL: (You can also query its corresponding permissions) Use MySQL; SELECT Host,user,pass

drop user user_name[,user_name2,...]; --View users Select User,host from Mysql.user; --View online users SELECT Substring_index (host, ': ', 1) as Host_short, NBSP ; Group_concat (DISTINCT user) as users, COUNT (*) as Threads N Bsp from Information_schema.processlist GROUP by Host_short NB Sp ORDER by COUNT (*), host_short; --Create a databaseCreate DATABASE db_name [default character set UTF8 collate utf8_general_ci]; Example : Create DATABASE School d

Public classMyObject {Private volatile StaticMyObject MyObject; PrivateMyObject () {} Public StaticMyObject getinstance () {Try { if(MyObject! =NULL){ }Else{Thread.Sleep (3000); synchronized(MyObject.class) { if(MyObject = =NULL) {MyObject=NewMyObject (); } } } } Catch(Exception e) {e.printstacktrace (); } returnMyObject; }}A single-instance mode of thread safety implemented by

We create a user using the DDL "create user" statement, and the new SQL user does not allow access to tables belonging to other SQL users, nor does it immediately create its own table, which must be authorized. The permissions that you can grant include the following groups: 1. Column permissions: Related to a specific column in the table 2. Table permissions: Related to all data in a specific

number of schemas is the same as the number of user, and the schema name corresponds to the user name one by one and the same, all we can call the schema as the user alias, although this is not accurate, but it is easier to understand some.A user has a default schema, whose schema name is equal to the user name, and of course a user can use other schemas. If we visit a table and do not indicate which schema the table belongs to, the system automatically adds the default Sheman name to the table

DCL, double check lock, central defender. In fact, the DCL many people in a single case mode used, LZ interview people also want them to write, but a lot of people will write wrong. Why would they write it wrong? Where is the source of the error? What are the solutions? The following is an analysis with the LZ.Problem analysisLet's look at the lazy type in the singleton pattern:Public Class Singleton { Priv