根据另一个表中存在的值在SELECT语句中设置列值

Question

I have 2 tables. One table lists all the records of items we track. The other table contains flags of attributes of the records in the first table.

For example, Table 1 has columns

Tab1ID, Name, Address, Phone

Table 2 has these columns

Tab2ID, Tab1ID, FlagName

There is a 1 to Many relationship between Table1 and Table2 linked by Tab1ID.

I'd like to create a query that has all the records from Table1 in it. However, if one of the records in Table2 has a Flagname=Retired (with a matching Tab1ID) then I want a "Y" to show up in the select column list otherwise an "N".

I think it might look something like this:

Select Name, Address, Phone, (select something in table2)
from Table1
where Tab1ID > 1;

It's the subquery in the column that has me stumped.

Pat

Answer 1

You can use exists :

Select t1.*,
       (case when exists (select 1
                          from table2 t2
                          where t2.tab1id = t1.tab1id and t2.flagname = 'Retired'
                         )
             then 'Y' else 'N'
       end) as retired_flag
from Table1 t1;

Answer 2

I would do a normal join returning multiple records, but convert them to bits with case statements. Then use that as the subquery and pull the max value for each bit column.

select
    name
    ,address
    ,phone
    ,max(retired_flag)
from (
    select
        table1.name
        ,table1.address
        ,table1.phone
        ,case when table2.flagname = 'retired' then 1 else 0 end as [retired_flag]
    from table1
    left join table2
        on table1.tab1id = table2.tab1id
    where tab1id > 1
    ) tbl
group by
    name
    ,address
    ,phone