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OracleDDL,DML,DCL,TCL基礎概念

2013-11-13 22:14:59  來源: Oracle 

  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 users 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


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