1. computed column

alter table tableName add columnName as (cast(aColumn as float) / bColumn * 100) persisted; 

2. unique nullable

create unique nonclustered index[UniqueName] on [tableName]([columnNameA] asc) where ([columnNameA] is not null);

3. foreign key cascade delete

alter table [tableNameA
 
] drop constraint [FKName];
alter table [tableNameA] with check add constraint [FKName] foreign key(foreignColumnName) references [tableNameB]([Id]) on delete cascade -- or on delete set null;

4. reset auto increment

dbcc checkident (‘tableName‘) --check current
dbcc checkident (‘tableName‘, reseed, 0
 
); --reset to 0 , next is 1

sql server 我常用的語句