BASIC SQL QUERIES:

What are the difference between DDL, DML and DCL commands? 


DDL is Data Definition Language statements. 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 
  • GRANT - gives user's access privileges to database 
  • REVOKE - withdraw access privileges given with the GRANT command


DML is Data Manipulation Language statements. Some examples: 
  • SELECT - retrieve data from the 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 
  • CALL - call a PL/SQL or Java subprogram 
  • EXPLAIN PLAN - explain access path to data 
  • LOCK TABLE - control concurrency


DCL is Data Control Language statements. Some examples:
  • 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 what rollback segment to use

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