15일차 # 6-15: PL/SQL Collections

  - 액세스시 색인/첨자(키 값)이 필요

  - 장점

1) simplify the code

2) loop through each element with ease by using collection built-in methods

3) improved performance - cache static data

  * Associative arrays (index-by tables)

: let you look up elements using arbitrary numbers and strings for subscript values.

          hash tables in other programming languages.

- sets of (unique index key, value) pairs

   1) 상대적으로 작은 룩업 테이블에 적합 <== 메모리에 생성되므로

   2) 크기를 미리 알 수 없는 집합 데이터에 적합 <== 크기 제한 없으므로

   3) 색인값이 유연(flexible) <== 색인값: 음수, 양수, 문자열 가능하고 nonsequential도 가능하므로

  * Nested tables

   1) hold an arbitrary number of elements.

   2) use sequential numbers as subscripts.

   3) can be sparse

   4) 데이터베이스 테이블에 저장 가능

  * Varrays (short for variable-size arrays)

   1) hold a fixed number of elements ==> 개수를 미리 알고 있을시 적합

   2) the number of elements can be changed at runtime.

   3) use sequential numbers as subscripts.

   4) 데이터베이스 테이블에 저장 가능

  * Choosing Which PL/SQL Collection Types to Use (When to use What?)

==> http://goo.gl/0dDcf

    - Varray

. Use to preserve ordered list

. Use when working with a fixed set, with a known number of entries

. Use when you need to store in the database and operate on the Collection as a whole

    - Nested Table

. Use when working with an unbounded list that needs to increase dynamically

. Use when you need to store in the database and operate on elements individually

    - Associative Array

. Use when there is no need to store the Collection in the database 

. Its speed and indexing flexibility make it ideal for internal application use