Oracle DDL,DML,DCL,TCL 入门概念


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



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