Help ,,,,,help

[david liu]

I have a problem that a sql sentence couldn't be performed by Mysql correctly!

the sql sentence as follows:

select * from
(select ....... ) as a ,
(select ........) as b where conditions.


Simply speaking , a and b are sets of rows ,but when this SQL sentence was performed by Mysql ,the resule is wrong. but I can get the right result through puting a and b to two new-created tables , and the I update the SQL sentence as follows:

select * from table c, table d where conditions

please tell me Why ! and how do I update the sentence.!! thank you !