A practical approach towards learning SQL in Oracle 11g. Video lectures are prepared as well and can be found at given link https://www.youtube.com/channel/UCMv6HrS_4_GFWmLLFzL_U_A?view_as=subscriber

1. SQL Fundamentals Oracle 11g
M U H A M M A D WA H E E D
O R AC L E DATA BA S E D E V E LO P E R
E M A I L : m .wa h e e d 3 6 6 8 @ g m a i l . co m
Lecture#7
SQL Joins/SELECT on Multiple Tables

2. Cartesian Product
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3. Cartesian Product(cont’d)
•A Cartesian product is formed when
- A join condition is omitted
- A join condition is invalid
- All rows are joined to the all rows in second table
•To avoid it, use valid join condition in WHERE clause
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4. Cartesian Product(cont’d)
•Example:
i- SELECT s.std_id, s.std_name,r.sub_id,r.obt_marks
FROM student s, result r;
ii- SELECT s.std_id, s.std_name,r.sub_id,r.obt_marks
FROM student s, result r
WHERE s.std_id = r.result_id;
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5. Types of Joins
There are following commonly used joins:
•Equijoin
•Non-equijoin
•Outer join
•Self join
*Note: join condition is always mentioned in WHERE clause
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6. Join Condition
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7. Equijoin
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8. Equijoin(cont’d)
•Example:
SELECT s.std_id, s.std_name, r.obt_marks
FROM student s, result r
WHERE s.std_id = r.std_id;
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9. Equijoin(cont’d)
•Example(additional search with join):
SELECT s.std_id, s.std_name, r.obt_marks
FROM student s, result r
WHERE s.std_id = r.std_id
AND r.obt_marks>65;
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10. Equijoin(cont’d)
•Example(more than two tables in join):
SELECT s.std_id, s.std_name,r.sub_id,r.obt_marks
FROM student s, result r, subject ss
WHERE s.std_id = r.std_id AND ss.sub_id = r.sub_id
AND r.obt_marks>65;
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11. Non-Equijoin
•A join condition containing something other than equality
operator.
•Example:
SELECT t.tch_id, t.tch_name,t.salary,s.sal_grade
FROM teacher t, salary_grade s
WHERE t.salary BETWEEN s.min_sal AND s.max_sal;
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12. Outer Join
•A join condition which is used to display those rows that doesn’t
meet join criteria.
•Outer join operator is plus sign ‘+’.
•There are two types of outer join
- Left outer join
- Right outer join
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13. Outer Join(cont’d)
•Example(left join):
SELECT s.std_id, s.std_name, r.obt_marks
FROM student s, result r
WHERE s.std_id (+)= r.std_id;
•Example(right join):
SELECT s.std_id, s.std_name, s.dept_id
FROM student s, department d
WHERE s.dept_id = d.dept_id(+);
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14. Self Join
•A join condition where a table having it’s own primary key
as foreign key in itself.
•Example: manager_id of employee table is employee_id
itself.
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15. Self Join(cont’d)
•Example:
SELECT a.emp_id,a.emp_name,a.manager_id
FROM employee a,employee b
WHERE a.manager_id = b.emp_id;
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