random choose small set of rows from oracle table

1) count total number of record from the table
    select count(*) from customers;

2)100 records out of 100000, is 100/100000 = 0.1 percent

3) use following query
  select * from customers SAMPLE(0.1), which will return 100 records randomly each time

Oracle nested collection test code

set SERVEROUT ON;
DECLARE

TYPE VARCHAR_TABLE IS TABLE OF VARCHAR2(64);
TYPE VC_VARCHAR_TABLE IS TABLE OF VARCHAR_TABLE INDEX BY VARCHAR2(64);

v_t1 VARCHAR_TABLE := VARCHAR_TABLE ('abc1','abc2','abc3');
v_t2 VARCHAR_TABLE := VARCHAR_TABLE();

v_t3 VC_VARCHAR_TABLE;

BEGIN
    v_t2.EXTEND(4);
    v_t2(1) := 'test1';
    v_t2(2) := 'test2';
    v_t2(3) := 'test3';
   
    DBMS_OUTPUT.PUT_LINE('VALUE in v_t1 3 is ' || v_t1(3));
    DBMS_OUTPUT.PUT_LINE('VALUE in v_t2 3 is ' || v_t2(3));
   
    v_t3('a1') := v_t1;
    v_t3('a2') := v_t2;
   
    DBMS_OUTPUT.PUT_LINE('VALUE in v_t3 2 is ' || v_t3('a2')(2));
   
END;
/



-----------------------------------------------------------------------------------------

VALUE in v_t1 3 is abc3
VALUE in v_t2 3 is test3
VALUE in v_t3 2 is test2


PL/SQL procedure successfully completed.

try rxjs in chrome devtool

1)  got o https://rxjs-dev.firebaseapp.com/
2) press F11 to open devtools, you should see the welcome messages, like this
 ____           _ ____     
|  _ \ __  __  | / ___|   
| |_) |\ \/ /  | \___ \ 
|  _ <  >  < |_| |___) |   
|_| \_\/_/\_\___/|____/

started experimenting with RxJS:

type this into the console:

rxjs.interval(500).pipe(rxjs.operators.take(4)).subscribe(console.log)

3) now you can type any code in console to test rxjs
4) one thing need pay attention is that do not use any import since we are inside the js document
if we want use anything in rxjx like this (import { scan } from 'rxjs/operators';)
we should  use it like this
 scan = rxjs.operators.scan;
 fromEvent = rxjs.fromEvent;
fromEvent(document, 'click') .pipe(scan(count => count + 1, 0)) .subscribe(count => console.log(`Clicked ${count} times`));