JV said:
What is a union query? When should it be used and when should it not be used?
A UNION query tacks the data records of one query onto the
data records of another query. E.g.if you have two tables:
table1:
nm v
--------
A 1
B 2
table 2
txt num
------------
X 3
Y 4
then the union query:
SELECT nm, v FROM table1
UNION
SELECT txt, num FROM table2
will return the data records:
nm v
--------
A 1
B 2
X 3
Y 4
UNION queries are rarely needed in a propery normalized
database.
