|PL/SQL User's Guide and Reference
Release 2 (9.2)
Part Number A96624-01
PL/SQL Language Elements, 7 of 52
A collection method is a built-in function or procedure that operates on collections and is called using dot notation. The methods
DELETE help generalize code, make collections easier to use, and make your applications easier to maintain.
NEXT are functions, which appear as part of an expression.
DELETE are procedures, which appear as a statement.
DELETE take integer parameters.
DELETE can also take
VARCHAR2 parameters for associative arrays with string keys.
TRIM cannot be used with index-by tables.
For more information, see "Using Collection Methods".
This identifies an index-by table, nested table, or varray previously declared within the current scope.
COUNT returns the number of elements that a collection currently contains, which is useful because the current size of a collection is not always known. You can use
COUNT wherever an integer expression is allowed.
COUNT always equals
LAST. For nested tables, normally,
LAST. But, if you delete elements from the middle of a nested table,
COUNT is smaller than
This procedure has three forms.
DELETE removes all elements from a collection.
DELETE(n) removes the
nth element from an index-by table or nested table. If
n is null,
DELETE(n) does nothing.
DELETE(m,n) removes all elements in the range
m..n from an index-by table or nested table. If
m is larger than
n or if
n is null,
DELETE(m,n) does nothing.
TRUE if the
nth element in a collection exists. Otherwise,
FALSE. Mainly, you use
DELETE to maintain sparse nested tables. You can also use
EXISTS to avoid raising an exception when you reference a nonexistent element. When passed an out-of-range subscript,
FALSE instead of raising
This procedure has three forms.
EXTEND appends one null element to a collection.
n null elements to a collection.
n copies of the
ith element to a collection.
EXTEND operates on the internal size of a collection. So, if
EXTEND encounters deleted elements, it includes them in its tally. You cannot use
EXTEND with index-by tables.
LAST return the first and last (smallest and largest) subscript values in a collection. The subscript values are usually integers, but can also be strings for associative arrays. If the collection is empty,
NULL. If the collection contains only one element,
LAST return the same subscript value.
FIRST always returns 1 and
LAST always equals
COUNT. For nested tables, normally,
COUNT. But, if you delete elements from the middle of a nested table,
LAST is larger than
This is an expression that must yield (or convert implicitly to) an integer in most cases, or a string for an associative array declared with string keys.
For nested tables, which have no maximum size,
NULL. For varrays,
LIMIT returns the maximum number of elements that a varray can contain (which you must specify in its type definition).
PRIOR(n) returns the subscript that precedes index
n in a collection.
NEXT(n) returns the subscript that succeeds index
n has no predecessor,
NULL. Likewise, if
n has no successor,
This procedure has two forms.
TRIM removes one element from the end of a collection.
n elements from the end of a collection. If
n is greater than
SUBSCRIPT_BEYOND_COUNT. You cannot use
TRIM with index-by tables.
TRIM operates on the internal size of a collection. So, if
TRIM encounters deleted elements, it includes them in its tally.
You cannot use collection methods in a SQL statement. If you try, you get a compilation error.
EXISTS can be applied to atomically null collections. If you apply another method to such collections, PL/SQL raises
You can use
NEXT to traverse collections indexed by any series of subscripts. For example, you can use
NEXT to traverse a nested table from which some elements have been deleted.
EXTEND operates on the internal size of a collection, which includes deleted elements. You cannot use
EXTEND to initialize an atomically null collection. Also, if you impose the
NULL constraint on a
VARRAY type, you cannot apply the first two forms of
EXTEND to collections of that type.
If an element to be deleted does not exist,
DELETE simply skips it; no exception is raised. Varrays are dense, so you cannot delete their individual elements.
PL/SQL keeps placeholders for deleted elements. So, you can replace a deleted element simply by assigning it a new value. However, PL/SQL does not keep placeholders for trimmed elements.
The amount of memory allocated to a nested table can increase or decrease dynamically. As you delete elements, memory is freed page by page. If you delete the entire table, all the memory is freed.
In general, do not depend on the interaction between
DELETE. It is better to treat nested tables like fixed-size arrays and use only
DELETE, or to treat them like stacks and use only
Within a subprogram, a collection parameter assumes the properties of the argument bound to it. So, you can apply methods
COUNT, and so on to such parameters. For varray parameters, the value of
LIMIT is always derived from the parameter type definition, regardless of the parameter mode.
In the following example, you use
NEXT to traverse a nested table from which some elements have been deleted:
i := courses.FIRST; -- get subscript of first element WHILE i IS NOT NULL LOOP -- do something with courses(i) i := courses.NEXT(i); -- get subscript of next element END LOOP;
In the following example, PL/SQL executes the assignment statement only if element
The next example shows that you can use
LAST to specify the lower and upper bounds of a loop range provided each element in that range exists:
In the following example, you delete elements 2 through 5 from a nested table:
In the final example, you use
LIMIT to determine if you can add 20 more elements to varray