oins and subqueries in big data analysis

1. JOINS AND SUBQUERIES IN
BIG DATAANALYSIS
N.SURATHAVANI MSc(IT)
Nadar Saraswathi College of Arts and Science,
Theni.

2. SQL JOIN:
A JOIN clause is used to combine rows from two or
more tables, based on a related column between them.
An SQL JOIN clause combines rows from two or
more tables. It creates a set of rows in a temporary
table.

3. Different Types of SQL JOINs:
JOIN (INNER)
LEFT (OUTER) JOIN
RIGHT (OUTER) JOIN
FULL (OUTER) JOIN

4. SQL INNER JOIN:
The INNER JOIN keyword selects records that have
matching values in both tables.
The INNER JOIN keyword selects all rows from
both tables as long as there is a match between the
columns.

5. INNER JOIN Syntax:
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

6. SQL LEFT JOIN:
The LEFT JOIN keyword returns all records from
the left table (table1), and the matched records from
the right table (table2).
The result is NULL from the right side, if there is no
match.
The LEFT JOIN keyword returns all records from
the left table (Customers), even if there are no
matches in the right table (Orders).

7. LEFT JOIN Syntax:
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

8. SQL RIGHT JOIN:
The RIGHT JOIN keyword returns all records from
the right table (table2), and the matched records from
the left table (table1).
The result is NULL from the left side, when there is
no match.
The RIGHT JOIN keyword returns all records from
the right table (Employees), even if there are no
matches in the left table (Orders).

9. RIGHT JOIN Syntax:
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;

10. SQL FULL OUTER JOIN:
The FULL OUTER JOIN keyword return all records
when there is a match in either left (table1) or right
(table2) table records.
FULL OUTER JOIN can potentially return very
large result-sets.
FULL OUTER JOIN and FULL JOIN are the same.

11. FULL OUTER JOIN Syntax:
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name
WHERE condition;

12. Subquery in SQL:
The subquery can be nested inside a SELECT,
INSERT, UPDATE, or DELETE statement or inside
another subquery.
A subquery is usually added within the WHERE
Clause of another SQL SELECT statement.
You can use the comparison operators, such as >, <,
or =. The comparison operator can also be a multiple-
row operator, such as IN, ANY, or ALL.

13. A subquery is also called an inner query or inner
select, while the statement containing a subquery is
also called an outer query or outer select.
A subquery must be enclosed in parentheses.
A subquery must be placed on the right side of the
comparison operator.

14. A subquery may occur in :
A SELECT clause
A FROM clause
A WHERE clause

16. Subqueries:
A subquery must be enclosed in parentheses.
A subquery must be placed on the right side of
the comparison operator.
Subqueries cannot manipulate their results
internally, therefore ORDER BY clause cannot
be added into a subquery.
Use single-row operators with single-row
subqueries