A PL/SQL block can contain a sub-block which can be placed in any section. The following describes the architecture of a PL/SQL block:

DECLARE: declares variables, types, cursors, and regional stored procedures and functions used in the PL/SQL block.
```
DECLARE
```
This part is optional if no variable needs to be declared.
- An anonymous block may omit the DECLARE keyword if no variable needs to be declared.
- For a stored procedure, AS is used, which is equivalent to DECLARE. The AS keyword must be reserved even if there is no variable declaration part.
EXECUTION: specifies procedure and SQL statements. It is the main part of a program. Mandatory
```
BEGIN
```
EXCEPTION: processes errors. Optional
```
EXCEPTION
```
END
```
END;
/
```
You are not allowed to use consecutive tabs in the PL/SQL block, because they may result in an exception when the parameter -r is executed using the gsql tool.

PL/SQL blocks are classified into the following types:

Anonymous block: a dynamic block that can be executed only for once. For details about the syntax, see Figure 1.
Subprogram: a stored procedure, function, operator, or packages stored in a database. A subprogram created in a database can be called by other programs.

Basic Structure