oracle group by语句实例测试

sql代码

create table test(a varchar2( 20),b varchar2 (20),c number,d varchar2 (20))

insert into test values( 'a1','b1' ,1, 't');
insert into test values( 'a3','b3' ,3, 't');
insert into test values( 'a4','b4' ,4, 't');
insert into test values( 'a2','b2' ,2, 't');
insert into test values( 'xx','xx' ,5, 'x');

insert into test values( 'a1','b1' ,1, 't');
insert into test values( 'a3','b3' ,3, 't');
insert into test values( 'a4','b4' ,4, 't');
insert into test values( 'a2','b2' ,2, 't');
insert into test values( 'xx','xx' ,5, 'x');
commit;

1.select a,b, sum(c) from test where d= 't' group by a,b order by a,b;

2.select a,b, sum(c) from test where d= 't' group by b,a order by a,b;

总结：对于1，2而言，结果应该是一样的，但是分组的顺序不同，sql的性能应该也是不同的。