我想把a列,b列,c列 合并成一列怎么处理?请前辈指点
------解决方案--------------------
select a from tablename
union all
select b as a from tablename
union all
select c as a from tablename
------解决方案--------------------
用UNION (ALL)
SELECT A FROM ...
UNION ALL SELECT B FROM...
UNION ALL SELECT C FROM...
------解决方案--------------------
select a from tablename
union all
select b as a from tablename
union all
select c as a from tablename