VARRAY是在Oracle8G的时候引入的一个类型，是一种密集填充数组，更容易被理解成为一个传统的数组。在创建这些数组的时候，都有一个尺寸，需要非常注意的是VARRAY的下表是从1开始的，在其他很多变成语言中，数组的下表都是从0开始的，比如JAVA。在实际的使用中，初学者经常会出现如下的错误提示：
ORA-06533:下表超出数量
例如下面的代码就会出现该错误:
DECLARE
TYPE NUM_VARRAY IS VARRAY(100) OF NUMBER NOT NULL;
V_NUM_VARRAY NUM_VARRAY:=NUM_VARRAY();
BEGIN
FOR J IN 1 .. 100 LOOP
V_NUM_VARRAY(J) := J;
END LOOP;
FOR I IN 1 .. V_NUM_VARRAY.COUNT LOOP
DBMS_OUTPUT.PUT_LINE(TO_CHAR(V_NUM_VARRAY(I)));
END LOOP;
END;
这个错误的原因是什么呢？我们定义了一个为空的VARRAY，在第一个J循环的时候，将1赋值给V_NUM_ARRAY(1)，但是因为实际上，该集合变量并没有存储空间，因此PL/SQL就会报一个“下表超出数量”的错误。
EXTEND is a procedure that adds elements to the end of a varray or nested table. The collection can be empty, but not null. (To make a collection empty or add elements to a null collection, use a constructor. For more information, see "Collection Constructors".)
The EXTEND method has these forms:
-
EXTEND appends one null element to the collection.
-
EXTEND(n) appends n null elements to the collection.
-
EXTEND(n,i) appends n copies of the ith element to the collection.
EXTEND operates on the internal size of a collection. That is, if DELETE deletes an element but keeps a placeholder for it, then EXTEND considers the element to exist.
Example 5-20 declares a nested table variable, initializing it with three elements; appends two copies of the first element; deletes the fifth (last) element; and then appends one null element. Because EXTEND considers the deleted fifth element to exist, the appended null element is the sixth element. The procedureprint_nt prints the nested table variable after initialization and after the EXTEND and DELETE operations. The type nt_type and procedure print_nt are defined inExample 5-6.
Example 5-20 EXTEND Method with Nested Table
DECLARE nt nt_type := nt_type(11, 22, 33); BEGIN print_nt(nt); nt.EXTEND(2,1); -- Append two copies of first element print_nt(nt); nt.DELETE(5); -- Delete fifth element print_nt(nt); nt.EXTEND; -- Append one null element print_nt(nt); END; /
Result:
nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 nt.(5) = 11 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 nt.(6) = NULL ---
上面的大意是：
上面出错的代码修改为如下可以正常运行了：
DECLARE
TYPE NUM_VARRAY IS VARRAY(100) OF NUMBER NOT NULL;
V_NUM_VARRAY NUM_VARRAY:=NUM_VARRAY();
BEGIN
FOR J IN 1 .. 100 LOOP
V_NUM_VARRAY.EXTEND;
V_NUM_VARRAY(J) := J;
END LOOP;
FOR I IN 1 .. V_NUM_VARRAY.COUNT LOOP
DBMS_OUTPUT.PUT_LINE(TO_CHAR(V_NUM_VARRAY(I)));
END LOOP;
END;