PL/SQL CHALLENGE 每日一题

newkid · 发表于 2011-10-11 05:49

gyhgood · 发表于 2011-10-11 08:27

太感谢了，上面的问题好多都看不懂。英文太差

选个D

gyhgood · 发表于 2011-10-11 08:38

被最后一句话忽悠了“当你删除一个元素后” ，直接跑去研究C D两个答案了

jboracle1981 · 发表于 2011-10-11 09:00

English没学好
看英文看得累死

这道题（A）应该是对的
（D）不确定

试了下，本以为(D)会报下标超出数量的错误。。。
真是基础不扎实啊

l_numbers.DELETE　和
l_numbers.DELETE (1);有那么大区别啊

demonat · 发表于 2011-10-11 09:40

总结下，EXTEND会分配一个NULL，EXTEND（N）会分配N个NULL，COUNT 会计算NULL，DELETE（N）会删除第N行，用占位符代替，COUNT不会计算占位符，DELETE直接释放内存，这样的理解对么

hanchangjin · 发表于 2011-10-11 09:44

我选A，我觉得删除后应该还会保留，所以count时是不会发生变化的，我没有动手实验，只是凭感觉选的，不知道对不!

gyhgood · 发表于 2011-10-11 09:51

本帖最后由 gyhgood 于 2011-10-11 09:51 编辑

我觉得这个DELETE(N)的时候有点像C里的memset

dingjun123 · 发表于 2011-10-11 11:00

所以，学好一门技术，难在细节啊
这些东西plsql reference都是有的

〇〇 · 发表于 2011-10-11 11:04

http://download.oracle.com/docs/cd/B13789_01/appdev.101/b10807/05_colls.htm#i27396
Counting the Elements in a Collection (COUNT Method)COUNT returns the number of elements that a collection currently contains:
DECLARE TYPE NumList IS TABLE OF NUMBER; n NumList := NumList(2,4,6,8); -- Collection starts with 4 elements.BEGIN dbms_output.put_line('There are ' || n.COUNT || ' elements in N.'); n.EXTEND(3); -- Add 3 new elements at the end. dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.'); n := NumList(86,99); -- Assign a completely new value with 2 elements. dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.'); n.TRIM(2); -- Remove the last 2 elements, leaving none. dbms_output.put_line('Now there are ' || n.COUNT || ' elements in N.');END;/COUNT is useful because the current size of a collection is not always known. For example, you can fetch a column of Oracle data into a nested table, where the number of elements depends on the size of the result set.
For varrays, COUNT always equals LAST. You can increase or decrease the size of a varray using the EXTEND and TRIM methods, so the value of COUNT can change, up to the value of the LIMIT method.
For nested tables, COUNT normally equals LAST. But, if you delete elements from the middle of a nested table, COUNT becomes smaller than LAST. When tallying elements, COUNT ignores deleted elements.

Increasing the Size of a Collection (EXTEND Method)To increase the size of a nested table or varray, use EXTEND.
You cannot use EXTEND with index-by tables.
This procedure has three forms:

EXTEND

EXTEND(n)

n

EXTEND(n,i) appends n copies of the ith element to a collection.

You cannot use EXTEND to add elements to an uninitialized.
If you impose the NOT NULL constraint on a TABLE or VARRAY type, you cannot apply the first two forms of EXTEND to collections of that type.
EXTEND operates on the internal size of a collection, which includes any deleted elements. If EXTEND encounters deleted elements, it includes them in its tally. PL/SQL keeps placeholders for deleted elements so that you can re-create them by assigning new values.
DECLARE TYPE NumList IS TABLE OF INTEGER; n NumList := NumList(2,4,6,8); x NumList := NumList(1,3); PROCEDURE print_numlist(the_list NumList) IS output VARCHAR2(128); BEGIN FOR i IN the_list.FIRST .. the_list.LAST LOOP output := output || NVL(TO_CHAR(the_list(i)),'NULL') || ' '; END LOOP; dbms_output.put_line(output); END;BEGIN dbms_output.put_line('At first, N has ' || n.COUNT || ' elements.'); n.EXTEND(5); -- Add 5 elements at the end. dbms_output.put_line('Now N has ' || n.COUNT || ' elements.');-- Elements 5, 6, 7, 8, and 9 are all NULL. print_numlist(n); dbms_output.put_line('At first, X has ' || x.COUNT || ' elements.'); x.EXTEND(4,2); -- Add 4 elements at the end. dbms_output.put_line('Now X has ' || x.COUNT || ' elements.');-- Elements 3, 4, 5, and 6 are copies of element #2. print_numlist(x);END;/When it includes deleted elements, the internal size of a nested table differs from the values returned by COUNT and LAST. For instance, if you initialize a nested table with five elements, then delete elements 2 and 5, the internal size is 5, COUNT returns 3, and LAST returns 4. All deleted elements, regardless of position, are treated alike.

Deleting Collection Elements (DELETE Method)This procedure has various forms:

DELETE

DELETE(n)

n

DELETE(n)

DELETE(m,n) removes all elements in the range m..n from an associative array or nested table. If m is larger than n or if m or n is null, DELETE(m,n) does nothing.

For example:
DECLARE TYPE NumList IS TABLE OF NUMBER; n NumList := NumList(10,20,30,40,50,60,70,80,90,100); TYPE NickList IS TABLE OF VARCHAR2(64) INDEX BY VARCHAR2(32); nicknames NickList;BEGIN n.DELETE(2); -- deletes element 2 n.DELETE(3,6); -- deletes elements 3 through 6 n.DELETE(7,7); -- deletes element 7 n.DELETE(6,3); -- does nothing since 6 > 3 n.DELETE; -- deletes all elements nicknames('Bob') := 'Robert'; nicknames('Buffy') := 'Esmerelda'; nicknames('Chip') := 'Charles'; nicknames('Dan') := 'Daniel'; nicknames('Fluffy') := 'Ernestina'; nicknames('Rob') := 'Robert'; nicknames.DELETE('Chip'); -- deletes element denoted by this key nicknames.DELETE('Buffy','Fluffy'); -- deletes elements with keys in this alphabetic rangeEND;/Varrays always have consecutive subscripts, so you cannot delete individual elements except from the end (by using the TRIM method).
If an element to be deleted does not exist, DELETE simply skips it; no exception is raised. PL/SQL keeps placeholders for deleted elements, so you can replace a deleted element by assigning it a new value.
DELETE lets you maintain sparse nested tables. You can store sparse nested tables in the database, just like any other nested tables.
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.

solomon_007 · 发表于 2011-10-11 16:44

A,D (经执行。。。)

[每日一题] PL/SQL CHALLENGE 每日一题