oracle集合union、union all、intersect、minus
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
