ddl是什么,电脑中的“DDL”是什么？

ＤＤＬ（Data Definition Language)

资料定语言是指对资料的格式和形态下定义的语言ddl是什么，他是每个资料库要建立时候时首先要面对的，举凡资料分哪些表格关系、表格内的有什麽栏位主键、表格和表格之间互相参考的关系等等，都是在开始的时候所必须规划好的。

动态连接库，安装程序时会建立一些连接。就算卸载也仅仅是把程序卸栽了，程序所建的库还再，所以优化大师会帮你优化，就是把这些连接删掉

ddl是动态链接库，很多程序删除了以后留下了一些空的链接文件，这些文件很多时没有用的，可以删除掉。

动态连接库

什么是oracle中的DDL？

  DDL

Data Definition Language (DDL) statements are used to define the database structure or schema。 Some examples:

CREATE – to create objects in the database

ALTER – alters the structure of the database

DROP – delete objects from the database

TRUNCATE – remove all records from a table, including all spaces allocated for the records are removed

COMMENT – add comments to the data dictionary

RENAME – rename an object

DML

Data Manipulation Language (DML) statements are used for managing data within schema objects。
   Some examples:

SELECT – retrieve data from the a database

INSERT – insert data into a table

UPDATE – updates existing data within a table

DELETE – deletes all records from a table, the space for the records remain

MERGE – UPSERT operation (insert or update)

CALL – call a PL/SQL or Java subprogram

EXPLAIN PLAN – explain access path to data

LOCK TABLE – control concurrency

DCL

Data Control Language (DCL) statements。
   Some examples:

GRANT – gives user’s access privileges to database

REVOKE – withdraw access privileges given with the GRANT command

TCL

Transaction Control (TCL) statements are used to manage the changes made by DML statements。
   It allows statements to be grouped together into logical transactions。
  

COMMIT – save work done

SAVEPOINT – identify a point in a transaction to which you can later roll back

ROLLBACK – restore database to original since the last COMMIT

SET TRANSACTION – Change transaction options like isolation level and what rollback segment to use。