UNION, UNION All, Minus, Intersect

1. SQL
Ahmed Farag
Information Systems Dept.
Faculty of Computers and Information
Menoufia University, Egypt.

2. Review
• Install MySQL, Work Bench
• Load sample Data to DB
• Select
• DISTINCT,
• WHERE, Not IN, IN, AND, OR, BETWEEN, Like, Is
null, Is Not Null, Alias
• Limit, Order by
• Sub Queries
• Trim function

3. Review
• MySQL single row functions (INSTR, CONCAT,
CONCAT_WS, FIND_IN_SET, Round, Truncate,
MOD, IFNULL, Format).
• MySQL multi row functions (AVG, Count, Sum,
MIN, MAX, ).
• Group by
• Having
• Join (Inner, left, right, cross, self), ON, Using

4. MySQL UNION

5. MySQL
UNION
operator
• MySQL UNION operator allows you to combine two or more
result sets of queries into a single result set.
• The following illustrates the syntax of the UNION operator:
SELECT column_list
UNION [DISTINCT | ALL]
SELECT column_list
UNION [DISTINCT | ALL]
SELECT column_list
...
• To combine result set of two or more queries using the UNION
operator, there are the basic rules that you must follow:
• First, the number and the orders of columns that appear
in all SELECT statements must be the same.
• Second, the data types of columns must be the same or
convertible.
• By default, the UNION operator removes duplicate rows even
if you don’t specify the DISTINCT operator explicitly.

6. MySQL
UNION
operator
• The following statement combines result sets returned from
t1 and t2 tables:
SELECT id
FROM t1
UNION
SELECT id
FROM t2;
ID
1
2
3
ID
2
3
4
t1 t2
Output
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 4 |
+----+
4 rows in set (0.00 sec)
Because the rows with value 2 and 3
are duplicates, the UNION operator
removed it and kept only distinct ones.

7. MySQL
UNION
ALL
operator
• The following statement combines result sets returned from
t1 and t2 tables: Using UNION ALL
SELECT id
FROM t1
UNION ALL
SELECT id
FROM t2;
ID
1
2
3
ID
2
3
4
t1 t2
If you use the UNION ALL explicitly, the
duplicate rows, if available, remain in the
result. Because UNION ALL does not need to
handle duplicates.
Output
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 2 |
| 3 |
| 4 |
+----+
6 rows in set (0.00 sec)

8. MySQL
UNION
operator
• Suppose you want to combine the first name and last name of
both employees and customers into a single result set, you
can use the UNION operator as follows:
SELECT
firstName,
lastName
FROM
employees
UNION
SELECT
contactFirstName,
contactLastName
FROM
customers;

9. MySQL
UNION
operator
• Suppose you want to combine the first name and last name of
both employees and customers into a single result set, you
can use the UNION operator as follows:
SELECT
firstName,
lastName
FROM
employees
UNION
SELECT
contactFirstName,
contactLastName
FROM
customers;
• As you can see, the MySQL UNION operator uses the column
names of the first SELECT statement for labeling the columns
in the output.

10. MySQL
UNION
operator
• If you want to use your own column aliases, you need to
specify them explicitly in the first SELECT statement as shown
in the following example:
SELECT
concat(firstName,' ',lastName) fullname
FROM
employees
UNION SELECT
concat(contactFirstName,' ',contactLastName)
FROM
customers;

11. MySQL
UNION
operator
• If you want to sort the result of a union, you use an ORDER
BY clause in the last SELECT statement as shown in the
following example:
• Notice that if you place the ORDER BY clause in each SELECT
statement, it will not affect the order of the rows in the final
result set.
SELECT
concat(firstName,' ',lastName) fullname
FROM
employees
UNION SELECT
concat(contactFirstName,' ',contactLastName)
FROM
customers
ORDER BY fullname;

12. MySQL MINUS

13. MySQL
MINUS
operator
• MINUS compares results of two queries and returns distinct
rows from the first query that aren’t output by the second
query.
• The following illustrates the syntax of the MINUS operator:
• The basic rules for a query that uses MINUS operator are the
following:
• The number and order of columns in both column_list_1
and column_list_2 must be the same.
• The data types of the corresponding columns in both
queries must be compatible.
SELECT column_list_1 FROM table_1
MINUS
SELECT columns_list_2 FROM table_2;

14. MySQL
MINUS
operator
• The following statement combines result sets returned from
t1 and t2 tables:
ID
1
2
3
ID
2
3
4
t1 t2
Output
+----+
| id |
+----+
| 1 |
+----+
1 rows in set (0.00 sec)
SELECT id FROM
t1
MINUS
SELECT id FROM
t2;

15. MySQL
MINUS
operator
• Unfortunately, MySQL does not support MINUS operator.
However, you can use the MySQL join or Subquery to simulate
it.
• To emulate the MINUS of two queries, you use the following
syntax:
SELECT
column_list
FROM
table_1
LEFT JOIN table_2 ON join_predicate
WHERE
table_2.id IS NULL;
OR
SELECT a.id
FROM table_1 as a
WHERE <Condition>
AND a.id NOT IN (SELECT b.id from table_2 as b where
<Condition>)

16. MySQL
MINUS
operator
• For example, the following query uses the LEFT JOIN clause to
return the same result as the MINUS operator:
SELECT
id
FROM
t1
LEFT JOIN
t2 USING (id)
WHERE
t2.id IS NULL;

17. MySQL INTERSECT

18. MySQL
INTERSECT
operator
• The INTERSECT operator is a set operator that returns only
distinct rows of two queries or more queries.
• The following illustrates the syntax of the INTERSECT operator.
• To use the INTERSECT operator for two queries, the following
rules are applied:
• The order and the number of columns must be the same.
• The data types of the corresponding columns must be
compatible.
(SELECT column_list
FROM table_1)
INTERSECT
(SELECT column_list
FROM table_2);

19. MySQL
INTERSECT
operator
• The following statement returns the distinct rows of both
result sets which include (2,3).
ID
1
2
3
ID
2
3
4
t1 t2
Output
+----+
| id |
+----+
| 2 |
| 3 |
+----+
2 rows in set (0.00 sec)
SELECT id FROM
t1
INTERSECT
SELECT id FROM
t2;
Unlike the UNION operator,
the INTERSECT operator returns
the intersection between two circles.

20. MySQL
MINUS
operator
• Unfortunately, MySQL does not support the INTERSECT
operator. However, you can simulate the INTERSECT operator.
• The following statement uses DISTINCT operator and INNER
JOIN clause to return the distinct rows in both tables:
SELECT DISTINCT
id
FROM t1
INNER JOIN t2 USING(id);
Output
id
----
2
3
How it works.
• The INNER JOIN clause returns rows
from both left and right tables.
• The DISTINCT operator removes the
duplicate rows.

21. MySQL
MINUS
operator
• The following statement uses the IN operator and a subquery
to return the intersection of the two result sets.
Output
id
----
2
3
How it works.
• The subquery returns the first result set.
• The outer query uses the IN operator to
select only values that are in the first
result set. The DISTINCT operator
ensures that only distinct values are
selected.
SELECT DISTINCT
id
FROM
t1
WHERE
id IN (SELECT
id
FROM
t2);