Collections in Oracle allow storing ordered groups of elements of the same data type, including index-by tables which are like hash tables, nested tables which are like sets, and vArrays which maintain order but have a fixed size; different collection types can be used as columns in database tables or passed as parameters between procedures; initializing, extending, counting, deleting, and retrieving elements from collections is done using collection methods.

1. Oracle - Collections Kaushik Raghupathi

2. What is a Collection Is an ordered group of elements of the same datatype Similar to Lists, Arrays PL/SQL has following collections Index by Tables vArrays Nested Tables Mapping from Other Languages Hash Tables are like Index by Tables Arrays are like vArrays Sets are like Nested Tables

3. Index by Table - Associative Array Associative arrays are sets of key-value pairs Each key can uniquely identify a value in the array DECLARE TYPE population_type IS TABLE OF NUMBER INDEX BY VARCHAR2(64); country_population population_type; howmany NUMBER; BEGIN country_population('Greenland') := 100000; country_population('Iceland') := 750000; howmany := country_population('Greenland'); END; /

4. Index by Table - Associative Array TYPE type_name IS TABLE OF [DATATYPE] INDEX BY [DATATYPE];

5. Nested Tables One Column Database Table No particular Order of storage Can have items deleted and sparse collections Typically unbounded DECLARE TYPE CourseList IS TABLE OF VARCHAR2(16); my_courses CourseList; BEGIN my_courses := CourseList('Econ 2010', 'Acct 3401', 'Mgmt 3100'); dbms_output.put_line(my_courses(1)); END; /

6. Nested Tables TYPE type_name IS TABLE OF [DATATYPE];

7. vArray Ordered group of Items Maximum size needs to be specified Small or uniform sized collections DECLARE TYPE CourseList IS VARRAY(50) OF VARCHAR2(16); my_courses CourseList; BEGIN my_courses := CourseList('Econ 2010', 'Acct 3401', 'Mgmt 3100'); END;

8. VARRAY TYPE type_name IS VARRAY(SIZE) of [DATATYPE];

9. Initializing, Extend, Count, Delete DECLARE TYPE CourseList IS VARRAY(50) OF VARCHAR2(16); my_courses CourseList; BEGIN my_courses := CourseList(); my_courses.EXTEND(2); dbms_output.put_line(my_courses.COUNT); select 'string' into my_courses(2) from dual; dbms_output.put_line(my_courses( 2)); my_courses.DELETE; END;

10. Key Aspects You need to initialize all vArray/Nested Table before assigning values You need to extend them to allocate their length You can use COUNT to check if the length For a vARRAY you can DELETE the whole array For a NESTED Table you can delete a specific element EXISTS(n) check if an nth element exists LIMIT return the maximum length of a VARRAY COUNT returns the count of elements of a collection Associative Arrays normally for Small Lookups in memory

11. Passing Collections as Parameters DECLARE TYPE Roster IS TABLE OF VARCHAR2(15); names Roster := Roster('J Hamil', 'D Piro', 'R Singh'); i BINARY_INTEGER := 2; BEGIN verify_name(names(i)); -- call procedure END;

12. Using Collections in Tables CREATE TYPE ProjectList AS VARRAY(50) OF VARCHAR2(16); / CREATE TABLE department ( -- create database table dept_id NUMBER(2), name VARCHAR2(15), budget NUMBER(11,2), -- Each department can have up to 50 projects. projects ProjectList) /

13. Using Collections in Tables INSERT INTO department VALUES(60, 'Security', 750400, ProjectList('New Badges', 'Track Computers', 'Check Exits')); Try selecting data from the table

14. Using Collections in Tables SELECT a.* FROM TABLE(SELECT projects FROM department) a