The Union Clause is used to combine two separate select
statements and produce the result set as a union of both the select statements.
NOTE:
- The fields to be used in both the selet statements must be in same order, same number and same data type.
- The Union clause produces distinct values in the result set, to fetch the duplicate values too UNION ALL must be used instead of just UNION.
Basic Syntax:
SELECT
column_name(s) FROM table1 UNION SELECT column_name(s) FROM table2;
Resultant
set consists of distinct values.
SELECT
column_name(s) FROM table1 UNION ALL SELECT column_name(s) FROM table2;
Resultant
set consists of duplicate values too.
Queries
- To fetch distinct ROLL_NO from Student and Student_Details table.
·
SELECT ROLL_NO FROM Student UNION
SELECT ROLL_NO FROM Student_Details;
Output:
ROLL_NO
|
1
|
2
|
3
|
4
|
- To fetch ROLL_NO from Student and Student_Details table including duplicate values.
·
SELECT ROLL_NO FROM Student UNION
ALL SELECT ROLL_NO FROM Student_Details;
Output:
ROLL_NO
|
1
|
2
|
3
|
4
|
3
|
2
|
- To fetch ROLL_NO , NAME from Student table WHERE ROLL_NO is greater than 3 and ROLL_NO , Branch from Student_Details table WHERE ROLL_NO is less than 3 , including duplicate values and finally sorting the data by ROLL_NO.
·
SELECT ROLL_NO,NAME FROM Student WHERE
ROLL_NO>3
·
UNION ALL
·
SELECT ROLL_NO,Branch FROM
Student_Details WHERE ROLL_NO<3 span="">3>
·
ORDER BY 1;
·
·
Note:The
column names in both the select statements can be different but the
·
data type must be same.And in the result set
the name of column used in the first
·
select statement will appear.
Output:
ROLL_NO
|
NAME
|
1
|
Information Technology
|
2
|
Computer Science
|
4
|
SURESH
|
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