Oracle：我可以创建一个约束来检查组内的值吗

Question

提前感谢您对此的帮助。在 Oracle 中，是否可以创建一个约束，以便每个组只能有一个 'leader'：

如果群组中已经存在一个 'leader'，我如何创建规则来阻止插入额外的 'leader'？

Answer 1

这有意义吗？基于函数的唯一索引：

SQL> create table test (col1 varchar2(10), col2 varchar2(10), col3 varchar2(10));

Table created.

SQL> create unique index ui1t on test (case when col2 = 'leader' then col1||col2 end);

Index created.

测试：

SQL> insert into test values ('group1', 'leader', 'joe');

1 row created.

SQL> insert into test values ('group1', null    , 'diane');

1 row created.

SQL> insert into test values ('group1', null    , 'john');

1 row created.

SQL> insert into test values ('group1', null    , 'diane');

1 row created.

SQL> insert into test values ('group1', 'leader', 'mike');   --> another LEADER for GROUP1
insert into test values ('group1', 'leader', 'mike')
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.UI1T) violated


SQL> insert into test values ('group1', 'leader', null);   --> another LEADER for GROUP1
insert into test values ('group1', 'leader', null)
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.UI1T) violated


SQL>

Oracle：我可以创建一个约束来检查组内的值吗

Oracle: can I create a constraint that checks a value within a group

oracle

triggers

database-design

constraints