私は以下の表を持って

Question

別のテーブルを結合するためのSQL：

私は選択なステートメントを書きたい、次の結果を表示

I参加しようとする/ユニオン/ユニオンすべての2つのテーブルが、私は砂漠の出力を取得しないでください。誰もそれで私を助けることができますか？

Answer 1

select 
'group_a' as groupname 
, max(case classname when 'C123' then group_a else null end) as c123 
, max(case classname when 'C456' then group_a else null end) as c456 
from table1 
union all 
select 
'group_b' as groupname 
, max(case classname when 'C123' then group_b else null end) as c123 
, max(case classname when 'C456' then group_b else null end) as c456 
from table1 
union all 
select 
'group_d' as groupname 
, max(case classname when 'C123' then group_d else null end) as c123 
, max(case classname when 'C456' then group_d else null end) as c456 
from table1 
union all 
select 
'group_e' as groupname 
, max(case classname when 'C123' then group_e else null end) as c123 
, max(case classname when 'C456' then group_e else null end) as c456 
from table1