去重有两层含义,一是记录完全一样。而是符合一定条件的认为是重复。
(
id number,
name varchar2(20),
remark varchar2(20)
);
insert into A_TEST (ID, NAME, REMARK)
values (1, 'a', 'ss');
insert into A_TEST (ID, NAME, REMARK)
values (2, 'b', 'xxx');
insert into A_TEST (ID, NAME, REMARK)
values (3, 'b', 'x');
insert into A_TEST (ID, NAME, REMARK)
values (4, 'b', 'asd');
insert into A_TEST (ID, NAME, REMARK)
values (5, 'c', 'axxx');
insert into A_TEST (ID, NAME, REMARK)
values (6, 'c', 'asdf');
from A_TEST a, (select min(id) as id from A_TEST t group by name) b
where a.id = b.id;

去重方式一(高效):
from (select a.*, rownum row_num from A_TEST a) x
where x.row_num in (select min(rownum) from A_TEST t group by name)

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