Join vs Union

Thanks

Hi Akash,

The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables.
The UNION operator is used to combine the result-set of two or more SELECT statements.The UNION operator selects only distinct values by default

JOIN is used to retrive data from different tables using a single sql statement.union is used to combine the results of two or more sql querries.


JOIN:
-----

A Join is used for displaying columns with the same or
different names from different tables. The output displayed
will have all the columns shown individually. i.e. The
columns will be aligned next to each other.

UNION:
------

The UNION set operator is used for combining data from two
tables which have columns with the same datatype.
When a UNION is performed the data from both tables will be
collected in a single column having the same datatype.

For eg:

See the two tables shown below:

Table t1

Articleno article price manufacturer_id
1 hammer 3 $ 1
2 screwdriver 5 $ 2

Table t2
manufacturer_id manufacturer
1 ABC Gmbh
2 DEF Co KG

Now for performing a JOIN type the query shown below

SELECT articleno, article, manufacturer
FROM t1 JOIN t2 ON (t1.manufacturer_id =
t2.manufacturer_id);

articelno article manufacturer
1 hammer ABC GmbH
2 screwdriver DEF Co KG

That is a join.

UNION means that you have to tables or resultset with the
same amount and type of columns and you add this to
tables/resultsets together. Look at this example:

Table year2006

Articleno article price manufacturer_id
1 hammer 3 $ 1
2 screwdriver 5 $ 2

Table year2007

Articleno article price manufacturer_id
1 hammer 6 $ 3
2 screwdriver 7 $ 4

SELECT articleno, article, price, manufactruer_id
FROM year2006
UNION
SELECT articleno, article, price, manufacturer_id
FROM year2007

articleno article price manufacturer_id
1 hammer 3 $ 1
2 screwdriver 5 $ 2
1 hammer 6 $ 3
2 screwdriver 7 $ 4






Thanks