create table NameInfo(WorkNo varchar(10), Name varchar(10))insert into NameInfo select 'A101' ,'李明' union all select 'A102' ,'李小明'create table tableC (Id int, WorkerNo varchar(10))insert into tableC select 1 ,'A101' union all select 2 ,'A102' union all select 3 ,'A103' goselect c.id,c.WorkerNo,isnull(n.name,'未知') as name from tablec c left join NameInfo n on c.WorkerNo = n.WorkNo /* id WorkerNo name 1 A101 李明 2 A102 李小明 3 A103 未知 */
select 'A101' ,'李明' union all
select 'A102' ,'李小明'create table tableC (Id int, WorkerNo varchar(10))insert into tableC
select 1 ,'A101' union all
select 2 ,'A102' union all
select 3 ,'A103'
goselect c.id,c.WorkerNo,isnull(n.name,'未知') as name
from tablec c
left join NameInfo n
on c.WorkerNo = n.WorkNo
/*
id WorkerNo name
1 A101 李明
2 A102 李小明
3 A103 未知
*/