在H2中删除列的唯一约束

Question

我尝试删除h2中以前创建为的列的唯一约束info varchar(255) unique。

我试过了：

sql> alter table public_partner drop constraint (select distinct unique_index_name from in
formation_schema.constraints where table_name='PUBLIC_PARTNER' and column_list='INFO');

但是没有成功（如下）：

Syntax error in SQL statement "ALTER TABLE PUBLIC_PARTNER DROP CONSTRAINT ([*]SELECT DISTI
NCT UNIQUE_INDEX_NAME FROM INFORMATION_SCHEMA.CONSTRAINTS WHERE TABLE_NAME='PUBLIC_PARTNER
' AND COLUMN_LIST='INFO') "; expected "identifier"; SQL statement:
alter table public_partner drop constraint (select distinct unique_index_name from informa
tion_schema.constraints where table_name='PUBLIC_PARTNER' and column_list='INFO') [42001-1
60]

如何正确消除此约束？

顺便一提：

sql> (select unique_index_name from information_schema.constraints where table_name='PUBLI
C_PARTNER' and column_list='INFO');
UNIQUE_INDEX_NAME
CONSTRAINT_F574_INDEX_9
(1 row, 0 ms)

似乎返回正确的输出。

Answer 1

在SQL语言中，标识符名称不能是表达式。您需要运行两个语句：

select distinct constraint_name from information_schema.constraints 
where table_name='PUBLIC_PARTNER' and column_list='INFO'

然后获取标识符名称，并运行该语句

ALTER TABLE PUBLIC_PARTNER DROP CONSTRAINT <xxx>