Index-by tables

Student table

STUDENT_ID	FIRST_NAME	LAST_NAME	CITY
1	Daniel	SCOTT	New York
2	Anthony	SIMMONS	Chicago
3	Sophia	THOMPSON	Los Angeles
4	Emily	PETERSON	Phoenix
5	David	DAWSON	Seattle
6	Gabriel	LEWIS	Boston
7	Natalie	MARTIN	Baltimore
8	Ava	GONZALES	Pasadena
9	Elliot	PETERSON	Chicago

Index-by tables(associative arrays)

DECLARE
	TYPE type_student IS TABLE OF VARCHAR2(200) INDEX BY VARCHAR2(200);
	adr_list type_student;
	v_address   VARCHAR2(200);
BEGIN
	adr_list('Los Angeles') := 'address_1';
	adr_list('Chicago') := 'address_2';
	adr_list('Seattle') := 'address_3';
	v_address := adr_list.FIRST;
	WHILE v_address IS NOT null LOOP 
		FOR x in (SELECT * FROM students WHERE city=v_address)
		LOOP
			DBMS_OUTPUT.PUT_LINE (x.student_id||' - '||x.first_name||' '||x.last_name||' - '||x.city);      
		END LOOP;
		v_address := adr_list.NEXT(v_address);
	END LOOP;
END;
/

Output

2 – Anthony SIMMONS – Chicago

9 – Elliot PETERSON – Chicago

3 – Sophia THOMPSON – Los Angeles

5 – David DAWSON – Seattle