text: SELECT BillingCountry, COUNT(Invoiceid) AS invoices_number
  FROM Invoice
  GROUP BY BillingCountry
  ORDER BY 2 DESC
  /
  SELECT /* +INDEX(Invoices(invoiceid)) */  BillingCountry, COUNT(Invoiceid) AS invoices_number
  FROM Invoice
  GROUP BY BillingCountry
  ORDER BY 2 DESC
  /
  
  analyze table invoice compute statistics;
  /
  
  CREATE INDEX idx_billingcountry ON invoice(BillingCountry);
  /
  
  SELECT
    FirstName || ' ' || LastName AS Name,
    CustomerId,
    Country
  FROM Customer
  WHERE Country <> 'USA';
  /
  SELECT t.Name, count(t.Name) AS TEST
  FROM Track t
  JOIN InvoiceLine l on l.TrackId =t.Trackid
  group by t.Name
  order by test desc
  FETCH FIRST 5 ROWS ONLY;
  /
  
  SELECT /*+ FIRST_ROWS(5) */ t.Name, count(t.Name) AS TEST
  FROM Track t
  JOIN InvoiceLine l on l.TrackId =t.Trackid
  group by t.Name
  order by test desc;
  /
  
  SELECT p.Name, COUNT(pt.TrackID) as Number_of_tracks
  FROM Playlist p JOIN playlisttrack pt
  using (playlistid)
  GROUP BY p.name;
  /
  
  select * from employee;
  /
  
  SELECT lastname, employeeid, reportsto , LEVEL  from employee 
  start with reportsto is null
  connect by prior employeeid = reportsto;
  
  
  
  SELECT lastname, employeeid from employee
  start with reportsto is null
  connect by prior employeeid = reportsto;
  /
  select * from employee;
  /
  select employeeid from employee;
  
  
  
  
  