SQL Commands

SQL commands fall under below categories.

• DDL ( Data Definition Language )
  • Interact directly with Database.
  • An implicit commit is applied before and after DDL commands.
  • Undo cannot be done on DDL
  • Following are DDL commands
    • Create
    • Alter
    • Truncate
    • Rename
    • Drop
    • FlashBack
    • Purge
    • Comment
• DML ( Data Manipulation Language )
  • Interact through buffer.
  • Slower compared to DDL due to buffer involvement.
  • As they applied to buffer they can be rolledback.
  • Categoriesed into
    • Read
      • Below is the command under this category
        • SELECT
    • Write
      • Below are the commands under this category:
        • INSERT
        • UPDATE
        • DELETE
        • MERGE
      • Row level locks are placed implicitly on the rows which are affected by these commands.
• TCL (Transaction Control Language )
  • Can be executed only under a transaction
  • Categorized into
    • Transaction : Starts with DML write obperation and ends with commit/rollback. The commit/rollback would be Implicit or Explicit.
    • Commit : This makes the changes permanent.
    • Rollback : Will undo the changes done by previous DML command.
    • Savepoint : A temporary saving point within a transaction.
• DCL (Data Control Language)
  • These commands directly interact with database.
  • These commands deal only with Privileges only
  • DCL commands enforce implicit commit before and after statement.
  • Rollback or Undo cannot be done on DCL statements.
  • DCL commands:
    • GRANT
    • REVOKE
    • SET ROLE

SQL commands summary Table