|PL/SQL User's Guide and Reference
10g Release 1 (10.1)
Part Number B10807-01
The basic program unit in PL/SQL is the block. A PL/SQL block is defined by the keywords
END. These keywords partition the block into a declarative part, an executable part, and an exception-handling part. Only the executable part is required. You can nest a block within another block wherever you can place an executable statement. For more information, see "Block Structure" and "Scope and Visibility of PL/SQL Identifiers".
Keyword and Parameter Description
Any scalar or user-defined PL/SQL datatype specifier such as
Signals the start of the executable part of a PL/SQL block, which contains executable statements. A PL/SQL block must contain at least one executable statement (even just the
Declares a collection (index-by table, nested table, or varray). For the syntax of
collection_declaration, see "Collections".
Declares a constant. For the syntax of
constant_declaration, see "Constants and Variables".
Applies only to datatypes that can be constrained such as
NUMBER. For character datatypes, this specifies a maximum size in bytes. For numeric datatypes, this specifies a maximum precision and scale.
Declares an explicit cursor. For the syntax of
cursor_declaration, see "Cursors".
Declares a cursor variable. For the syntax of
cursor_variable_declaration, see "Cursor Variables".
Signals the start of the declarative part of a PL/SQL block, which contains local declarations. Items declared locally exist only within the current block and all its sub-blocks and are not visible to enclosing blocks. The declarative part of a PL/SQL block is optional. It is terminated implicitly by the keyword
BEGIN, which introduces the executable part of the block.
PL/SQL does not allow forward references. You must declare an item before referencing it in any other statements. Also, you must declare subprograms at the end of a declarative section after all other program items.
Signals the end of a PL/SQL block. It must be the last keyword in a block. Remember,
END does not signal the end of a transaction. Just as a block can span multiple transactions, a transaction can span multiple blocks.
Signals the start of the exception-handling part of a PL/SQL block. When an exception is raised, normal execution of the block stops and control transfers to the appropriate exception handler. After the exception handler completes, execution proceeds with the statement following the block.
If there is no exception handler for the raised exception in the current block, control passes to the enclosing block. This process repeats until an exception handler is found or there are no more enclosing blocks. If PL/SQL can find no exception handler for the exception, execution stops and an unhandled exception error is returned to the host environment. For more information, see Chapter 10.
Declares an exception. For the syntax of
exception_declaration, see "Exceptions".
Associates an exception with a sequence of statements, which is executed when that exception is raised. For the syntax of
exception_handler, see "Exceptions".
Declares a function. For the syntax of
function_declaration, see "Functions".
An undeclared identifier that optionally labels a PL/SQL block. If used,
label_name must be enclosed by double angle brackets and must appear at the beginning of the block. Optionally,
label_name (not enclosed by angle brackets) can also appear at the end of the block.
A global identifier declared in an enclosing block can be redeclared in a sub-block, in which case the local declaration prevails and the sub-block cannot reference the global identifier unless you use a block label to qualify the reference, as the following example shows:
<<outer>> DECLARE x INTEGER; BEGIN DECLARE x INTEGER; BEGIN IF x = outer.x THEN -- refers to global x NULL; END IF; END; END outer; /
Declares an instance of an object type. For the syntax of
object_declaration, see "Object Types".
Declares a procedure. For the syntax of
procedure_declaration, see "Procedures".
Declares a user-defined record. For the syntax of
record_declaration, see "Records".
An executable (not declarative) statement that. A sequence of statements can include procedural statements such as
RAISE, SQL statements such as
UPDATE, and PL/SQL blocks.
A user-defined subtype that was defined using any scalar or user-defined PL/SQL datatype specifier such as
Declares a variable. For the syntax of
variable_declaration, see "Constants and Variables".
PL/SQL supports a subset of SQL statements that includes data manipulation, cursor control, and transaction control statements but excludes data definition and data control statements such as
The following PL/SQL block declares some variables, executes statements with calculations and function calls, and handles errors that might occur:
DECLARE numerator NUMBER := 22; denominator NUMBER := 7; the_ratio NUMBER; BEGIN the_ratio := numerator/denominator; dbms_output.put_line('Ratio = ' || the_ratio); EXCEPTION WHEN ZERO_DIVIDE THEN dbms_output.put_line('Divide-by-zero error: can''t divide ' || numerator || ' by ' || denominator); WHEN OTHERS THEN dbms_output.put_line('Unexpected error.'); END; /