sql server 我常用的语句

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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

 

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