两张表,通过fileid关联,表一的fileid可空。id fileid
--------------
1
2 222
3 333
fileid filename
----------------------
222 "222.avi"
333 "333.avi"
查询id和filename的对应关系,如果fileid为空,则输出空。id filename
----------------------
1 ""
2 "222.avi"
3 "333.avi"
--------------
1
2 222
3 333
fileid filename
----------------------
222 "222.avi"
333 "333.avi"
查询id和filename的对应关系,如果fileid为空,则输出空。id filename
----------------------
1 ""
2 "222.avi"
3 "333.avi"
from ta a
left join tb b
on a.fileid = b.fileid
from ta a left join tb b on a.fileid = b.fileid