Answer Posted / nikhila reddy

UNION:the both tables should have same structure and datatype.
the column name will taken as first table ones it wont bother abt other tables.
example:
emp table as
eid ename esal
1 a 10k
2 b 20k

dept table as
deptid deptname deptsal
11 aa 20k
12 bb 50k


select * from emp
union
select * from dept

empid empname empsal
1 a 10k
2 b 20k
11 aa 20k
12 bb 50k

now u can observe col name taking alias of first table.
no need of relation between a tables.
it will remove duplicate records.


joins:it will join only required fields from different tables.
no need of same structure for tables..
it should have relation between a tables.

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