oracle中集合的效率比普通的比较要高

 

测试案例

--测试表数据

SQL> select stuid from zr_stu;
 
      STUID
-----------
          1
          2
          3
          4
          5
          6
          7
 
7 rows selected
 
Executed in 0.14 seconds

--表数据

SQL> select stuid from zr_stu where stuid > 3;
 
      STUID
-----------
          4
          5
          6
          7
 
Executed in 0.047 seconds
 
SQL> select stuid from zr_stu where stuid < 6;
 
      STUID
-----------
          1
          2
          3
          4
          5
 
Executed in 0.109 seconds

--union

SQL> select stuid from zr_stu where stuid > 4 union select stuid from zr_stu where stuid < 6;
 
     STUID
----------
         1
         2
         3
         4
         5
         6
         7
 
7 rows selected
 
Executed in 0.031 seconds

--union all

SQL> select stuid from zr_stu where stuid > 4 
  2  union all 
  3  select stuid from zr_stu where stuid < 6;
 
     STUID
----------
         5
         6
         7
         1
         2
         3
         4
         5
 
8 rows selected
 
Executed in 0.156 seconds

--intersect

SQL> select stuid from zr_stu where stuid > 4 
  2  intersect 
  3  select stuid from zr_stu where stuid < 6;
 
     STUID
----------
         5
 
Executed in 0.078 seconds

--minus

SQL> select stuid from zr_stu where stuid > 4
  2  minus 
  3  select stuid from zr_stu where stuid < 6;
 
     STUID
----------
         6
         7
 
Executed in 0.062 seconds