2. Disclaimer: This presentation is prepared by trainees of
baabtra as a part of mentoring program. This is not official
document of baabtra –Mentoring Partner
Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt .
Ltd

3. JOINS AND UNION IN MySQL
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4. JOINS AND UNION
IN
MySQL

5. JOIN
• To query data from two or more tables, based on a relationship between
certain column in these tables.
• Tables in a database are often related to each other with keys.
• Primary key is a column (or a combination of columns) with a unique
value for each row.
• Foreign Key in one table points to a Primary Key in another table.

6. Different JOINs in MySQL
INNER JOIN(JOIN):
Return rows when there is at least one match in both tables.
LEFT JOIN:
Return all rows from the left table, even if there are no matches
in the right table.
RIGHT JOIN:
Return all rows from the right table, even if there are no matches in the left
table.
FULL JOIN:
Return rows when there is a match in one of the tables.
But It does not support in MySQL.

7. Tbl_dept
pk_dept_id dept_name
1 CSE
2 ECE
3 EEE
4 CE

8. tbl_student
pk_student_id student_name student_place fk_dept_id
1 baabtra1 Calicut 1
2 baabtra2 cochin 2
3 baabtra3 Kannur 3
4 baabtra4 ooty 3
5 baabtra5 munnar 1
6 baabtra6 mlp NULL

9. INNER JOIN (JOIN)
• The INNER JOIN keyword returns rows when there is at least one match in
both tables.
Syntax:
SELECT
column name(s)
FROM
table_name1
INNER JOIN
table_name2
ON
table_name1.column_name=table_name2.column_name
Tbl_dept Tbl_student

10. INNER JOIN Example
student_name dept_name
baabtra1 CSE
baabtra5 CSE
baabtra2 ECE
baabtra3 EEE
baabtra4 EEE
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
JOIN tbl_student
ON tbl_dept.pk_dept_id = tbl_student.fk_dept_id;

11. LEFT JOIN
• The LEFT JOIN keyword returns all rows from the left table (table_name1),
even if there are no matches in the right table (table_name2).
Syntax:
SELECT
column_name(s)
FROM
table_name1
LEFT JOIN
table_name2
ON
table_name1.column_name=table_name2.column_name.
Tbl_dept Tbl_student

12. LEFT JOIN Example
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
LEFT JOIN tbl_student
ON tbl_dept.pk_dept_id = tbl_student.fk_dept_id;
student_name dept_name
Baabtra1 CSE
Baabtra5 CSE
Baabtra2 ECE
Baabtra3 EEE
Baabtra4 EEE
NULL CE

13. RIGHT JOIN
• The RIGHT JOIN keyword returns all the rows from the right table
(table_name2), even if there are no matches in the left table (table_name1).
Syntax:
SELECT
column_name(s)
FROM
table_name1
RIGHT JOIN
table_name2
ON
table_name1.column_name=table_name2.column_name.
Tbl_dep Tbl_student

14. RIGHT JOIN Example
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
RIGHT JOIN tbl_student
ON tbl_dept.pk_dept_id = tbl_student.fk_dept_id;
Student_name Dept_name
Baabtra1 CSE
Baabtra2 ECE
Baabtra3 EEE
Baabtra4 EEE
Baabtra5 CSE
Baabtra6 NULL

15. FULL JOIN
• There is no FULL JOIN in MySQL.
• We can possible this by using both LEFT and RIGHT Joins together with
UNION key word.
Tbl_dep Tbl_student

16. UNION
• The UNION operator combines two or more SELECT statements.
• The UNION operator is used to combine the result-set of two or more
SELECT statements.
• Each SELECT statement within the UNION must have the same number of
columns.
• The columns must also have similar data types.
• The columns in each SELECT statement must be in the same order.

17. UNION Syntax
SELECT column _ name(s)
FROM Table_name1
UNION
SELECT column _ name(s)
FROM table_name2
• The column names in the result-set of a UNION are always equal to the
column names in the first SELECT statement in the UNION.

18. UNION ALL
• The UNION operator selects only distinct values by default. If you need to
allow duplicate values, use UNION ALL.
Syntax
SELECT column_name (s) FROM table_name1
UNION ALL
SELECT column_name(s) FROM table_name2

19. UNION Example
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
LEFT JOIN tbl_student
ON tbl_dept.pk_dept_id = tbl_student.fk_dept_id
UNION
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
RIGHT JOIN tbl_student
ON tbl_dept.pk_dept_id = tbl_student.fk_dept_id;

20. Student_name Dept_name
Baabtra1 CSE
Baabtra5 CSE
Baabtra2 ECE
Baabtra3 EEE
Baabtra4 EEE
NULL CE
Baabtra6 NULL

21. UNION ALL Example
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
LEFT JOIN tbl_student
ON tbl_dept.pk_dept_id=tbl_student.fk_dept_id
UNION ALL
SELECT tbl_student.student_name,tbl_dept.dept_name
FROM tbl_dept
RIGHT JOIN tbl_student
ON tbl_dept.pk_dept_id=tbl_student.fk_dept_id;

22. Student_name Dept_name
Baabtra1 CSE
baabtra5 CSE
baabtra2 ECE
baabtra3 EEE
baabtra4 EEE
NULL CE
baabtra1 CSE
baabtra2 ECE
baabtra3 EEE
baabtra4 EEE
baabtra5 CSE
baabtra6 NULL

23. SELECT tbl_dept.dept_name
FROM tbl_dept
UNION
SELECT tbl_student.student_name
FROM tbl_student;
dept_name
CSE
ECE
EEE
CE
Baabtra1
Baabtra2
Baabtra3
Baabtra4
Baabtra5
baabtra6

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