从oracle数据库检索数据所需的时间

SQL> create table t 
  2  as select rownum x1,rownum x2,rownum x3,rownum x4
  3  from ( select 1 from dual connect by level <= 10000 ),
  4       ( select 1 from dual connect by level <= 1000 );

Table created.

-- scanning but not fetching all the rows

SQL>
SQL> 
SQL> set timing on
SQL> select max(x1) from t;

   MAX(X1)
----------
  10000000

Elapsed: 00:00:00.72

-- fetching every row back to the calling environment

SQL> set timing on
SQL> begin
  2    for i in ( select * from t )
  3    loop
  4       null;
  5    end loop;
  6  end;
  7  /

PL/SQL procedure successfully completed.

Elapsed: 00:00:11.45
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