在H2中删除列的唯一约束

Question

我尝试删除以前创建的h2中的列的唯一约束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]

如何正确删除此约束？

顺便说说:

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>

Answer 2

您可以使用用户定义的函数来执行动态创建的语句.首先创建execute别名(只有一次):

CREATE ALIAS IF NOT EXISTS EXECUTE AS $$ void executeSql(Connection conn, String sql) 
throws SQLException { conn.createStatement().executeUpdate(sql); } $$;

然后调用此方法:

call execute('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'));

... execute运行语句的用户定义函数在哪里.