SQL Topics

7/30/2019 SQL Topics

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SQL

TOPICSByNaresh Kumar B. N


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INDEX1. JOINS ............................................................................................................................. 3

1.1 Types of Joins ............................................................................................................... 3

1.1.1 Equi join ................................................................................................................. 3

1.1.2 Cross Joins .............................................................................................................. 4

1.1.3 Self Joins ................................................................................................................ 4

1.1.4 Inner Joins .............................................................................................................. 4

1.1.5 Outer Joins ............................................................................................................. 5

2. MERGE ........................................................................................................................... 7

2.1 Sub query ..................................................................................................................... 73. UNION ........................................................................................................................... 8

4. PROCEDURES ................................................................................................................. 9


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1. JOINS

A join is a query that combines rows from two or more tables or views. Most join queries

contain at least one join condition. Joins are needed when the required data is stored inmore than one table. The tables that I am using are as follows,

DEPARTMENT

Department_ID Name Location_ID

10 Prime sourcing 122

20 Flex cube 124

30 OFSAA 123

40 NGP 167

1.1 Types of Joins1.1.1 Equi join

An equi join is a join with a join condition containing an equality operator. An equijoin

combines rows that have equivalent values for the specified columns.

Example: To Display employees with their designations

Select e.employee_id, e.employee_name, j.designationFrom employee e, job j

Where e.job_id=j.job_id;

EMPLOYEE_ID EMPLOYEE_NAME DESIGNATION

37252 NARESH Asst.Consultant

37251 CHAITANYA Asst.Consultant

37254 RAVI Staff consultant

37255 KASHYAP Sr.Consultant

LOCATION

Location_ID Location

122 bangalore

123 Chennai

124 Mumbai

167 Delhi

JOB

Job_ID Designation

667 Asst.Consultant

668 Sr.Consultant

669 Staff consultant

EMPLOYEE

EMPLOYEE

_ID

EMPLOYEE_

NAME

JOB_

ID

MANAGE

R_ID

DATE_OF_

JOIN

SALAR

Y

DEPARTMENT_

ID37252 NARESH 667 7902 13-08-2012 25000 10

37251 CHAITANYA 667 7698 20-02-2010 25000 30

37254 RAVI 669 7839 04-04-2009 30000 10

37255 KASHYAP 668 7839 15-06-2012 35000 40


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1.1.2 Cross Joins

If you dont specify the join condition it will automatically results in cross join or Cartesian

product of the participating tables. This join combines each row of one table with each

row of the other.

Example:

Select d.name, l. location

From location l, d.department;

Name Location

Prime sourcing BANGALORE

Prime sourcing CHENNAI

Prime sourcing MUMBAI

Prime sourcing DELHI

Flex cube BANGALORE

Flex cube CHENNAIFlex cube MUMBAI

Flex cube DELHI

OFSAA BANGALORE

OFSAA CHENNAI

OFSAA MUMBAI

OFSAA DELHI

NGP BANGALORE

NGP CHENNAI

NGP MUMBAI

NGP DELHI

1.1.3 Self Joins

A self join is a join of a table to itself. You can notice the same table name used twice in

the from clause with aliases.

Example: To Show the no. of employees working under every manager.

Select m.manager_id, count (*) from employee e,

employee m where e.employee_id=m.manager_id group bym.manager_id

1.1.4 Inner Joins

An inner join (sometimes called a simple join) is a join of two or more tables that returns

only those rows that satisfy the join condition.

Example: TO Display the employees with their department name and location.

Select employee_id, employee_name,name

from employee e, department dwhere e.department_id=d.department_id;

OR

Select employee_id, employee_name, name

From employee e inner join department dOn e.department_id=d.department_id;


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Employee_id employee_name name

37254 RAVI Prime sourcing

37252 NARESH Flex cube

37251 CHAITANYA OFSAA

37255 KASHYAP NGP

1.1.5 Outer Joins

An outer join returns all rows that satisfy the join condition and also returns some or all of

those rows from one table for which no rows from the other satisfy the join condition.

There are different types of outer joins.

They are

1.1.5.1 Left Outer Join

This join returns all the rows which satisfy the join condition and also the rows from left

table of the condition which does not satisfy the condition.Example: Display employee details with all departments.

Select last_name, d.department_id, d.nameFrom employee e, department d

Where e.department_id (+) = d.department_id;

Or

Select last_name, d.department_id, d.namefrom employee left outer join department d on

e.department_id = d.department_id;

Last_name Department_id Name

RAVI 10 Prime sourcing

NARESH 20 Flex cube

CHAITANYA 30 OFSAA

KASHYAP 40 NGP

1.1.5.2 Right outer join

This join returns all the rows which satisfy the join condition and also the rows from right

table of the condition which does not satisfy the condition.

Example:

Select e.employee_name, d.department_id, d.namefrom employee e right outer join department d one.department_id=d.department_id and d.name in('Prime sourcing', 'NGP');



20 Flex cube

30 OFSAA

KASHYAP 40 NGP


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1.1.5.3 Full outer join

This join returns all the rows which satisfy the join condition and also the rows from both

the tables of the condition which does not satisfy the condition.

Example:

Select e.employee_name, d.department_id, d.nameFrom employee e full outer join department d one.department_id=d.department_id and d.name in ('Primesourcing', 'NGP');



20 Flex cube

30 OFSAA

KASHYAP 40 NGP

CHAITANYANARESH


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2. MERGE

We will use the MERGE statement to select rows from one or more sources for update or

insertion into a table or view. You can specify conditions to determine whether to update

or insert into the target table or view.Consider the following tables for example

Now, if I want to add 20 marks for each student in STUDENT2 when id matches otherwiseinsert the non existing records into STUDENT2

Merge into STUDENT2 s2 USING (select id, nameFrom STUDENT) s1 ON (s2.id=s1.id)

When matched thenupdate set s2.marks=s2.marks+20When not matched then

insert (id, MARKS) values (s1.id, 15);

ID MARKS

37252 70

37253 50

37251 15

37250 15

2.1 Sub query

A subquery is a SELECT statement which is used in another SELECT statement. Subqueries

are very useful when you need to select rows from a table with a condition that depends

on the data of the table itself. You can use the subquery in the SQL clauses including

WHERE clause, HAVING clause, FROM clause etc.

Example: To Find out no.of employees working in prime sourcing department.

SELECT * FROM EMPLOYEEWHEREDEPARTMENT_ID= (SELECT DEPARTMENT_IDFROM DEPARTMENTWHERE NAME='Prime sourcing);

EMPLOYE

E_ID

EMPLOYE

E_NAMEJOB_ID

MANAGER

_ID

DATE_OF

_JOINSALARY

DEPARTM

ENT_ID

NARESH 37252 667 7902 13-AUG-12 25000 10RAVI 37254 669 7839 04-APR-09 30000 10

Student1

ID NAME37252 Naresh

37251 Chaitanya

37250 Kashyap

37253 Ravi

Student 2

ID MARKS

37252 50

37253 30


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3. UNION

UNION takes as arguments two nested tables and returns a nested table whose values

are those of the two input nested tables. The two input nested tables must be of the same

type, and the returned nested table is of the same type as well.

The ALL keyword instructs Oracle to return all elements that are in the two inputs

nested tables, including duplicate values and duplicate NULL occurrences. This is the

default.

The DISTINCT keyword instructs Oracle to eliminate duplicates from the returned

nested table, including duplicates ofNULL, if they exist.

Example:

List out the ALL designations in prime sourcing and Ngp

SELECT DESIGNATIONFROM JOBWhere job_id in(SELECT JOB_IDFROM EMPLOYEEWHERE DEPARTMENT_ID= (SELECT DEPARTMENT_IDFROM DEPARTMENT WHERE NAME=NGP))

UNIONSELECT DESIGNATIONFROM JOBWHERE JOB_ID IN

(SELECT JOB_IDFROM EMPLOYEEWHERE DEPARTMENT_ID= (SELECT DEPARTMENT_IDFROM DEPARTMENTwhere name='OFSAA'));

Output:

DESIGNATION

Asst.Consultant

Sr.Consultant


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4. PROCEDURES

A procedure is a named PL/SQL block which performs one or more specific task.

Procedure has a header and a body. The header consists of the name of the procedure

and the parameters or variables passed to the procedure. The body consists ordeclaration section, execution section and exception section similar to a general PL/SQL

Block.

Example: Procedure for giving the details of employee where employee id given as an

input parameter.

Pl/SQL

Create or replaceProcedure myproc(EID IN NUMBER) asENAME varchar2 (20);

DOJ DATE;BeginSELECT EMPLOYEE_NAME, DATE_OF_JOIN INTO ENAME, DOJ FROMNBN_EMPLOYE WHERE EMPLOYEE_ID=EID;DBMS_OUTPUT.PUT_LINE ('EMPLOYEE_NAME:'||ENAME);DBMS_OUTPUT.PUT_LINE ('DATE_OF_JOIN:'||DOJ);End;

SQL

EXECUTE myproc(37252);

Output:

EMPLOYEE_NAME: NARESHDATE_OF_JOIN:13-AUG-12

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