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SQL>
SQL> create table test
2 (
3 data_time VARCHAR2(20),
4 region_name VARCHAR2(100),
5 group_id VARCHAR2(20)
6 );
Table created
SQL> -- CREATE UNIQUE INDEX T_GROUPFORBIDDENBOARD_time_id
SQL> -- ON T_GROUPFORBIDDENBOARD(NVL2(data_time,group_id,NULL));
SQL> insert into test(data_time, group_id) values('201805','12');
1 row inserted
SQL> insert into test(data_time, group_id) values('201806','12');
1 row inserted
SQL> -- 观察一下这个结果
SQL> select NVL2(data_time,group_id,NULL) new_value from test;
NEW_VALUE
--------------------
12
12
SQL> drop table test purge;
Table dropped
SQL>