A Simple PL/SQL Block:
Each PL/SQL program consists of SQL and PL/SQL statements which from a PL/SQL block.PL/SQL Block consists of three sections:
- The Declaration section (optional).
- The Execution section (mandatory).
- The Exception Handling (or Error) section (optional).
Declaration Section:
The Declaration section of a PL/SQL Block starts with the reserved keyword DECLARE. This section is optional and is used to declare any placeholders like variables, constants, records and cursors, which are used to manipulate data in the execution section. Placeholders may be any of Variables, Constants and Records, which stores data temporarily. Cursors are also declared in this section.
Execution Section:
The Execution section of a PL/SQL Block starts with the reserved keyword BEGIN and ends with END. This is a mandatory section and is the section where the program logic is written to perform any task. The programmatic constructs like loops, conditional statement and SQL statements form the part of execution section.
Exception Section:
The Exception section of a PL/SQL Block starts with the reserved keyword EXCEPTION. This section is optional. Any errors in the program can be handled in this section, so that the PL/SQL Blocks terminates gracefully. If the PL/SQL Block contains exceptions that cannot be handled, the Block terminates abruptly with errors.
Every statement in the above three sections must end with a semicolon
; . PL/SQL blocks can be nested within other PL/SQL blocks. Comments can be used to document code.
How a Sample PL/SQL Block Looks
| DECLARE
Variable declaration
BEGIN
Program Execution
EXCEPTION
Exception handling
END; |
SQL Command Categories
SQL commands are grouped into four major categories depending on their functionality. They are as follows:
Data Definition Language (DDL)
These SQL commands are used for creating, modifying, and dropping the structure of database objects. The commands are CREATE, ALTER, DROP, RENAME, and TRUNCATE.
Data Manipulation Language (DML)
These SQL commands are used for storing, retrieving, modifying, and deleting data. These commands are SELECT, INSERT, UPDATE, and DELETE.
Transaction Control Language (TCL)
These SQL commands are used for managing changes affecting the data. These commands are COMMIT, ROLLBACK, and SAVEPOINT.
Data Control Language (DCL)
These SQL commands are used for providing security to database objects. These commands are GRANT and REVOKE.
