Example table

7/30/2019 Example table

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Learning Oracle SQL

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[Note : If any queries or doubts, please post it in the comments in this blog]

The following tables represent data about employees, skills, projects, project teams.The columns, their description and some sample data is provided. (If value is blank, treat them as

null)

Main Tables

Employee_Portfolio

emp_id emp_name Designation join_date supervisor_id

Uniqueidentifier

Name ofemployee

code that represents the designation.Refers to designation master (lookup)

table

Date ofoining

Employee id ofsupervisor

3251 Mark C2 12-1-2004

4562 Ryan C1 12-12-2000 3251

9812 Brian C1 12-12-2008 4562

CREATE:Code:SQL> create table employee_portfolio (emp_id varchar2(10),emp_name

varchar2(30),designation varchar2(20) ,join_date date,supervisor_id varchar2(20), foreign key(designation)references master_designation_details(designation),unique(emp_id));

Table created.

INSERTCode:SQL> insert into employee_portfolio values('&emp_id','&emp_name','&designation',to_date('&join_date','dd-mm-yyyy'),'&supervisor_id');

Enter value for emp_id: 3251

Enter value for emp_name: MarkEnter value for designation: C2Enter value for join_date: 12-1-2004Enter value for supervisor_id:old 1: insert into employee_portfolio values('&emp_id','&emp_name','&designation',to_date('&join_new 1: insert into employee_portfolio values('3251','Mark','C2',to_date('12-1-2004','dd-mm-yyyy')

1 row created.
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SQL> /Enter value for emp_id: 4562Enter value for emp_name: RyanEnter value for designation: C1Enter value for join_date: 12-12-2000Enter value for supervisor_id: 3251old 1: insert into employee_portfolio values('&emp_id','&emp_name','&designation',to_date('&join_new 1: insert into employee_portfolio values('4562','Ryan','C1',to_date('12-12-2000','dd-mm-yyyy'

1 row created.

SQL> /Enter value for emp_id: 9812Enter value for emp_name: BrianEnter value for designation: C1Enter value for join_date: 12-12-2008Enter value for supervisor_id: 4562

old 1: insert into employee_portfolio values('&emp_id','&emp_name','&designation',to_date('&join_new 1: insert into employee_portfolio values('9812','Brian','C1',to_date('12-12-2008','dd-mm-yyyy

1 row created.

SELECTCode:SQL> select * from employee_portfolio;

EMP_ID EMP_NAME DESIGNATION JOIN_DATESUPERVISOR_ID---------- ------------------------------ -------------------- --------- ----

----------------3251 Mark C2 12-JAN-044562 Ryan C1 12-DEC-00 32519812 Brian C1 12-DEC-08 4562

Employee_Skill

emp_id skill_id date_effective prof_level exp_years

Unique identifier of

employee whose

skills androficiency is

recorded. Refers to

employee master

table.


skill for which

employeesroficiency level is

recorded. Refers to

skill master (lookup)

table

Date when

employee got

the skill

Proficiency level

of given employee

or given skill.Takes values E0

thru E4

No. of years of

experience the

employee hason the given

skill

3251 C 12-12-2006 E1 3

3251 JAV 12-12-2004 E2 4

4562 DES 12-12-2008 E0 0

CREATE


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Code:SQL> create table employee_skill (emp_id varchar2(20),skill_idvarchar2(30),date_effective date,prof_level varchar2(20),exp_years varchar2(20),foreign key(emp_id) referencesemployee_portfolio(emp_id));

Table created.INSERTCode:SQL> insert into employee_skill values('&emp_id','&skill_id',to_date('&date_effective','dd-mm-yyyy'),'&prof_level','&exp_years');Enter value for emp_id: 3251Enter value for skill_id: CEnter value for date_effective: 12-12-2006Enter value for prof_level: E1Enter value for exp_years: 3old 1: insert into employee_skill values('&emp_id','&skill_id',to_date('&date_effective','dd-mm-y

new 1: insert into employee_skill values ('3251','C',to_date('12-12-2006','dd-mm-yyyy'),'E1','3')

1 row created.

SQL> /Enter value for emp_id: 3251Enter value for skill_id: JAVEnter value for date_effective: 12-12-2004Enter value for prof_level: E2Enter value for exp_years: 4old 1: insert into employee_skill values('&emp_id','&skill_id',to_date('&date_effective','dd-mm-ynew 1: insert into employee_skill values ('3251','JAV',to_date('12-12-

2004','dd-mm-yyyy'),'E2','4'

1 row created.

SQL> /Enter value for emp_id: 4562Enter value for skill_id: DESEnter value for date_effective: 12-12-2008Enter value for prof_level: E0Enter value for exp_years: 0old 1: insert into employee_skill values('&emp_id','&skill_id',to_date('&date_effective','dd-mm-ynew 1: insert into employee_skill values ('4562','DES',to_date('12-12-

2008','dd-mm-yyyy'),'E0','0'

1 row created.

SELECTCode:SQL> select * from employee_skill;

EMP_ID SKILL_ID DATE_EFFE PROF_LEVELEXP_YEARS


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-------------------- ------------------------------ --------- -------------------- -----------------3251 C 12-DEC-06 E133251 JAV 12-DEC-04 E244562 DES 12-DEC-08 E00

Employee_Project

project_id date_start date_end Name

Unique identifier of project whose

team is enlisted in the table

Date when project

started

Date when project

ended / ends

Name of project

2056 1-1-2008 Google Testing

2078 1-1-2007 12-12-2007 YahooDevelopment

CREATECode:SQL> create table employee_project(project_id varchar2(20),date_startdate,date_end date,Name varchar2(30));

Table created.

INSERTCode:SQL> insert into employee_projectvalues('&project_id',to_date('&date_start','dd-mm-yyyy'),to_date('&date_end','dd-mm-yyyy'),'&Name');Enter value for project_id: 2056Enter value for date_start: 1-1-2008

Enter value for date_end:Enter value for name: Google Testingold 1: insert into employee_projectvalues('&project_id',to_date('&date_start','dd-mm-yyyy'),to_danew 1: insert into employee_project values('2056',to_date('1-1-2008','dd-mm-yyyy'),to_date('','dd-

1 row created.

SQL> /Enter value for project_id: 2078Enter value for date_start: 1-1-2007Enter value for date_end: 12-12-2007

Enter value for name: Yahoo Developmentold 1: insert into employee_projectvalues('&project_id',to_date('&date_start','dd-mm-yyyy'),to_danew 1: insert into employee_project values('2078',to_date('1-1-2007','dd-mm-yyyy'),to_date('12-12-

1 row created.

SELECTCode:


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SQL> select * from employee_project;

PROJECT_ID DATE_STAR DATE_END NAME-------------------- --------- --------- ------------------------------2056 01-JAN-08 Google Testing2078 01-JAN-07 12-DEC-07 Yahoo Development

Employee_Project_Team

emp_id project_id date_start date_end role_id


employee worked

/works in the project.

Refers to employeetable


roject whose team is

enlisted in the table.

Refers to Projects table

Date when

employee got into

roject in the

given role

Date when

employee was

released from

roject if any

Role played

by employee

in project

3251 2056 1-1-2008 11-12-2008 DES

3251 2056 12-12-2008 MGR

4562 2056 12-12-2008 DEV

3251 2078 1-1-2007 12-12-2007 DES

CREATECode:SQL> create table Employee_project_team(emp_id varchar2(20),project_idvarchar2(30),date_start date,date_end date,role_id varchar2(20),foreign key(emp_id) referencesEmployee_portfolio(emp_id),foreignkey (project_id) references employee_project(project_id));

Table created.

INSERTCode:SQL> insert into employee_project_teamvalues('&emp_id','&project_id',to_date('&date_start','dd-mm-yyyy'),to_date('&date_end','dd-mm-yyyy'),'&role_id');Enter value for emp_id: 3251Enter value for project_id: 2056Enter value for date_start: 1-1-2008Enter value for date_end: 11-12-2008Enter value for role_id: DESold 1: insert into employee_project_teamvalues('&emp_id','&project_id',to_date('&date_start','dd-new 1: insert into employee_project_team values('3251','2056',to_date('1-1-2008','dd-mm-yyyy'),to_

1 row created.

SQL> /Enter value for emp_id: 3251Enter value for project_id: 2056Enter value for date_start: 12-12-2008Enter value for date_end:Enter value for role_id: MGRold 1: insert into employee_project_teamvalues('&emp_id','&project_id',to_date('&date_start','dd-


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new 1: insert into employee_project_team values('3251','2056',to_date('12-12-2008','dd-mm-yyyy'),t

1 row created.

SQL> /Enter value for emp_id: 4562Enter value for project_id: 2056Enter value for date_start: 12-12-2008Enter value for date_end:Enter value for role_id: DEVold 1: insert into employee_project_teamvalues('&emp_id','&project_id',to_date('&date_start','dd-new 1: insert into employee_project_team values('4562','2056',to_date('12-12-2008','dd-mm-yyyy'),t

1 row created.

SQL> /Enter value for emp_id: 3251

Enter value for project_id: 2078Enter value for date_start: 1-1-2007Enter value for date_end: 12-12-2007Enter value for role_id: DESold 1: insert into employee_project_teamvalues('&emp_id','&project_id',to_date('&date_start','dd-new 1: insert into employee_project_team values('3251','2078',to_date('1-1-2007','dd-mm-yyyy'),to_

1 row created.

SELECTCode:SQL> select * from employee_project_team;

EMP_ID PROJECT_ID DATE_STAR DATE_ENDROLE_ID-------------------- ------------------------------ --------- --------- --------------------3251 2056 01-JAN-08 11-DEC-08 DES3251 2056 12-DEC-08 MGR4562 2056 12-DEC-08 DEV3251 2078 01-JAN-07 12-DEC-07 DES

Master Tables

Master_Skill

skill_idName

C C Programming

JAV Java Programming

DES Software Design

TEST Software Testing

OOP Object Oriented Programming

CREATE


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Code:SQL> create table master_skill(skill_id varchar2(20),skill_namevarchar2(30),primary key(skill_id));Table created.

INSERTCode:

SQL> insert into master_skill values('&skill_id','&skill_name');Enter value for skill_id: CEnter value for skill_name: C Programmingold 1: insert into master_skill values('&skill_id','&skill_name')new 1: insert into master_skill values('C','C Programming')

1 row created.

SQL> /Enter value for skill_id: JAVEnter value for skill_name: Java Programmingold 1: insert into master_skill values('&skill_id','&skill_name')new 1: insert into master_skill values('JAV','Java Programming')

1 row created.

SQL> /Enter value for skill_id: DESEnter value for skill_name: Software Designold 1: insert into master_skill values('&skill_id','&skill_name')new 1: insert into master_skill values('DES','Software Design')

1 row created.

SQL> /Enter value for skill_id: TestEnter value for skill_name: Software Testing

old 1: insert into master_skill values('&skill_id','&skill_name')new 1: insert into master_skill values('Test','Software Testing')

1 row created.

SQL> /Enter value for skill_id: OOPEnter value for skill_name: Object Oriented Programmingold 1: insert into master_skill values('&skill_id','&skill_name')new 1: insert into master_skill values('OOP','Object Oriented Programming')

1 row created.

SELECT

Code:SQL> select * from master_skill;

SKILL_ID SKILL_NAME-------------------- ------------------------------C C ProgrammingJAV Java ProgrammingDES Software DesignTest Software TestingOOP Object Oriented Programming


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Master_Designation_details

DesignationName

C1 Engineer

C2 Analyst

C3 Consultant

C4 Director

VP Vice President

CREATECode:SQL> create table master_designation_details(designationvarchar2(20),designation_name varchar2(30),primary key(designation));

Table created.

INSERTCode:SQL> insert into master_designation_detailsvalues('&designation','&designation_name');Enter value for designation: C1Enter value for designation_name: Engineerold 1: insert into master_designation_detailsvalues('&designation','&designation_name')new 1: insert into master_designation_details values('C1','Engineer')

1 row created.

SQL> /

Enter value for designation: C2Enter value for designation_name: Analystold 1: insert into master_designation_detailsvalues('&designation','&designation_name')new 1: insert into master_designation_details values('C2','Analyst')

1 row created.

SQL> /Enter value for designation: C3Enter value for designation_name: Consultantold 1: insert into master_designation_detailsvalues('&designation','&designation_name')new 1: insert into master_designation_details values('C3','Consultant')

1 row created.

SQL> /Enter value for designation: C4Enter value for designation_name: Directorold 1: insert into master_designation_detailsvalues('&designation','&designation_name')new 1: insert into master_designation_details values('C4','Director')


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1 row created.

SQL> /Enter value for designation: VPEnter value for designation_name: Vice Presidentold 1: insert into master_designation_detailsvalues('&designation','&designation_name')new 1: insert into master_designation_details values('VP','Vice President')

1 row created.

SELECTCode:SQL> select * from master_designation_details;

DESIGNATION DESIGNATION_NAME-------------------- ------------------------------C1 Engineer

C2 AnalystC3 ConsultantC4 DirectorVP Vice President

Master_Role

role_idName

DES Designer

MGR Manager

DEV Developer

SC Site Coordinator

TST Tester

CREATECode:SQL> create table master_role(role_id varchar2(20),role_namevarchar2(30),primary key(role_id));

Table created.

INSERTCode:SQL> insert into master_role values('&role_id','&role_name');Enter value for role_id: DESEnter value for role_name: Designer

old 1: insert into master_role values('&role_id','&role_name')new 1: insert into master_role values('DES','Designer')

1 row created.

SQL> /Enter value for role_id: MGREnter value for role_name: Managerold 1: insert into master_role values('&role_id','&role_name')new 1: insert into master_role values('MGR','Manager')


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1 row created.

SQL> /Enter value for role_id: DEVEnter value for role_name: Developerold 1: insert into master_role values('&role_id','&role_name')new 1: insert into master_role values('DEV','Developer')

1 row created.

SQL> /Enter value for role_id: SCEnter value for role_name: Site Coordinatorold 1: insert into master_role values('&role_id','&role_name')new 1: insert into master_role values('SC','Site Coordinator')

1 row created.

SQL> /

Enter value for role_id: TSTEnter value for role_name: Testerold 1: insert into master_role values('&role_id','&role_name')new 1: insert into master_role values('TST','Tester')

1 row created.

SELECTCode:SQL> select * from master_role;

ROLE_ID ROLE_NAME-------------------- ------------------------------DES Designer

MGR ManagerDEV DeveloperSC Site CoordinatorTST Tester

Answer the following

For all questionsfollowing standard procedure starting from defining the problemto showing sample output / dry run.

Do not forget to explicitly articulate any assumptions you make Add sufficient sample data to the above data (do not remove any existing data)so

that you can demonstrate good output for all the following SQL and DML that you

will design. Inputs are specifically left as generic with examples so that youmay demonstrate

results for multiple inputs where needed

1. Find the names of all employees who are currently in projects and are whose designation


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is as given (say C1).

STEP 1: Problem Definiton:o Context

a. Employee_portfolio table has employee detailsname and designation

b. Employee_Project_Team has details of all employees who were / are working on agiven project

c. If date_end is null, then the project is the currently active project for the givenemployee

o InputA designation code

o OutputList of names of employees

a. With the given designation

b. Who are currently active in at least one project

o Special considerations

a. Same employee is active on multiple projects? b. Multiple employees match the requirement c. No employees match the requirement

o Sample scenario - Input C1 => Output Ryan

STEP 2: Solution Approach:

Find employees who are currently active:

o Criteriaend_date is null in employee_project_team table o Output required for further matchingemp_id o Intermediate solution: SELECT emp_id from employee_ project_team

where date_end is null

Get employee name based on previously got ids

o Criteriadesignation is as given in input on the employee table o Addl. Criteriaemp_id in output of previous query


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o Output required: emp_name o Intermediate solution: select emp_name from employee_portfolio where designation = ? and emp_id in ?previous_output?

NOTE: Approach can be reversed to filter first by designation as wellSTEP 3: Sample Test Cases

1. Input C2 => Output Mark

2. Input C1 => Output Ryan3. Input VP => Output None

NOTEMissing test case: multiple output scenario

Need to add data to demonstrate multiple records

This step can also be interchanged with step 2STEP 4: Dry Run

1. Intermediate result of query irrespective of input is 3251, 45622. Mapped names are: Mark, Ryan

3. If input is

a. C1further filter on employee returns Ryan b. C2further filter on employee returns Mark c. VP - further filter on employee returns no result

NOTE: Dry run will vary if approach is reversed

STEP 5: Translation Approach

The translation approach is depicted as sub-bullets (Intermediate Solution) in STEP 2: Solution

approach.

NOTE:

Though intermediate solution is inserted aboveit is expected that the part is filled only at thispoint of time. Insertion is done above just to show mapping between these steps

Also note that intermediate solution testing is skipped as this is a solution for a paper test.

STEP 6: Final Query

Code:SQL> select emp_name from employee_portfolio where designation = 'C1'andemp_id in (SELECT emp_id from employee_project_team where date_end is null);


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EMP_NAME------------------------------Ryan

OR

Code:SQL> select distinct emp_name from employee_portfolio e inner joinemployee_project_team pe on pe.emp_id = e.emp_id where designation = 'C1' and date_end is null;

EMP_NAME------------------------------Ryan

OR

Code:SQL> select emp_name from employee_portfolio e inner join (SELECT emp_id,date_end from employee_pr

oject_team where date_end is null) pe on pe.emp_id = e.emp_id wheredesignation = 'C1' and date_endis null;

EMP_NAME------------------------------Ryan

2. For each project, find the number of employees who have a particular skill (say JAV).

STEP 1: Problem Definiton:o Context

a. Employee_Skills table has details about skills of a given employee b. Project_Team table has details of all employees who were / are working on a given

project c. Project table has name of project

o InputA skill id

o OutputList of names of projects and corresponding number of employees

a. with the given skill

o Special considerations


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a. The project may have no team at all b. None of the team may have the skill c. Multiple employees have skills in the same project d. The same employee may have been on multiple roles in a given project - - in this case

he should not be double counted

e. The same employee may have worked on multiple projectsin this case doublecounting is fine.

o Sample scenario - Input JAV => Output

a. Google Testing 1 b. Yahoo Development 1

o Sample scenario - Input DES => Output

a. Google Testing 1 b. Yahoo Development 0

o

STEP 2: Final Query

Code:SQL> SELECT p.name, count(distinct pe.emp_id) No_of_Employee fromemployee_project p left outer joinemployee_project_team pe on p.project_id = pe.project_id left outer joinemployee_skill es on es.emp_id = pe.emp_id where skill_id = 'JAV' or skill_id is null group by p.name

2 /

NAME NO_OF_EMPLOYEE------------------------------ --------------Google Testing 1Yahoo Development 1

OR

Code:SQL> SELECT p.name, count(emp_id) No_of_Employee from employee_project p leftouter join (SELECT distinct project_id, emp_id from employee_project_team where emp_id in (selectemp_id from employee_skill where skill_id = 'JAV')) pe on p.project_id = pe.project_id group byp.name;


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ORCode:

SQL> SELECT p.name, count(pe.emp_id) No_of_Employee from employee_project pleft outer join (SELECTdistinct project_id, pt.emp_id from employee_project_team pt INNER JOINemployee_skill es ON es.emp_id = pt.emp_id where skill_id = 'JAV') pe on p.project_id = pe.project_idgroup by p.name;


Typical Mistakes

o If count(*) is done instead then all places where 0 is expected will return 1

o If outer join not done some records will be skippedo While doing outer join if OR skill_id is null check is not added some records will be skipped

o If group by not done correctly or if additional fields selected etc, query will not execute

o and many more

3. Find all people (name and total experience in given skill) who have a particular skill at a

particular proficiency (say JAV E2) who are not currently in any project.

Code:SQL> SELECT emp_name, exp_years from employee_portfolio e inner joinemployee_skill es on e.emp_id =es.emp_id where skill_id = 'JAV' and prof_level = 'E2' and NOT EXISTS(SELECT 1 FROM employee_project_team pt where pt.emp_id = e.emp_id and date_end is null);

no rows selected

OR

Code:SQL> SELECT emp_name, exp_years from employee_portfolio e inner joinemployee_skill es on e.emp_id =es.emp_id where skill_id = 'JAV' and prof_level = 'E2' and e.emp_id not in(SELECT emp_id from employee_project_team where date_end is null);


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no rows selected

4. Find all people (name of employee, designation name, project name and total experience

in given skill) who have a particular skill at a particular proficiency (say JAV E2);

Code:SQL> SELECT emp_name, exp_years, d.designation_name, p.name project_name fromemployee_portfolio e inner join employee_skill es on e.emp_id = es.emp_id left outer joinmaster_designation_details d ond.designation = e.designation left outer join employee_project_team pt onpt.emp_id = e.emp_id leftouter join employee_project p on pt.project_id = p.project_id where skill_id= 'JAV' and prof_level= 'E2' and pt.date_end is null;

EMP_NAME EXP_YEARS DESIGNATION_NAMEPROJECT_NAME

------------------------------ -------------------- ------------------------------ -----------------Mark 4 AnalystGoogle Testing

Typical Mistakes

o If date_end criteria is not used the same employee will appear multiple times for each of thepast projects (A valid assumption is that there is a max of one current project in which employee

works)

o If inner join done on project_team or project, then people not in any projects will not be listed

o While it may be okay to assume that there are matching designation rows and hence inner joinis also okayinner join on projects is not acceptable

5. Find all employees who report to an employee (say Ryan) who are not currently in any

project

Code:SQL> select e.emp_name from employee_portfolio e inner joinemployee_portfolio sup on e.supervisor_id = sup.emp_id where sup.emp_name = 'Ryan' and e.emp_id not in (SELECTemp_id from employee_project_team where date_end is null);

EMP_NAME------------------------------Brian

6. Find the employees (name, designation, current project name and role name if any) who

are second level reportees of a given employee (say Mark)

Code:


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SQL> select e.emp_name, d.designation_name, p.name project_name, r.role_namefrom employee_portfolio e inner join employee_portfolio sup on e.supervisor_id = sup.emp_id innerjoin employee_portfoliosup2 on sup.supervisor_id = sup2.emp_id left outer joinmaster_designation_details d on d.designation = e.designation left outer join employee_project_team pt on pt.emp_id =e.emp_id and pt.date_end is null left outer join employee_project p on pt.project_id = p.project_idleft outer join master_role r on pt.role_id = r.role_id where sup2.emp_name = 'Mark';

EMP_NAME DESIGNATION_NAME PROJECT_NAMEROLE_NAME------------------------------ ------------------------------ ------------------------------ -------Brian Engineer

7. Create report with the following details of all employees (employee id, name, designation,

supervisor id, supervisor name, supervisor designation) List them by designations (higher

levels first) and within that all names should be alphabetical.

Code:SQL> select e.emp_id, e.emp_name, e.designation, sup.emp_id supervisor_id,sup.emp_name supervisor_name, sup.designation supervisor_designation from employee_portfolio e leftouter join employee_portfolio sup on e.supervisor_id = sup.emp_id order by e.designation desc,e.emp_name;

EMP_ID EMP_NAME DESIGNATION SUPERVISORSUPERVISOR_NAME SUPERVISOR_DESIGNATI---------- ------------------------------ -------------------- ---------- --------------------------3251 Mark C29812 Brian C1 4562Ryan C14562 Ryan C1 3251Mark C2

8. Provide complete details of all current and previous projects of all employees reporting

to a given employee (say Mark)

Code:SQL> select e.*, p.*, pt.* from employee_portfolio e inner joinemployee_portfolio sup on e.superv

isor_id = sup.emp_id left outer join employee_project_team pt on pt.emp_id =e.emp_id left outer join employee_project p on pt.project_id = p.project_id where sup.emp_name ='Mark';

EMP_ID EMP_NAME DESIGNATION JOIN_DATESUPERVISOR_ID PROJECT_ID DATE_STAR DATE---------- ------------------------------ -------------------- --------- -------------------- ------


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4562 Ryan C1 12-DEC-00 32512056 01-JAN-08 Google Testing

9. An employee (say Mark) is handing over charge to a new employee (say Terry). Write

the necessary DML to add the new employee details and change the hierarchy of all

reportees of the original employee to the new employee.

INSERT:

Code:SQL> insert into employee_portfolio values('1234','Terry','C2','12-MAY-2004','');

1 row created.

UPDATE:

Code:SQL> UPDATE employee_portfolio set supervisor_id='1234' where

supervisor_id='3251';

1 row updated.

10. Check for all projects that have been ended in the past (end_date not null) and update

the project role end date of all employees who are active (end_date null) to the actual end

date of the project

Code:SQL> update employee_project_team set date_end = (select date_end fromemployee_project where date_end is not null) where project_id =(select project_id from employee_project

where date_end is not null) and date_end is null;

0 rows updated.

11. Find the employee who has the maximum number of direct reportees.

Code:SQL> select s.emp_id, s.emp_name from employee_portfolio s inner joinemployee_portfolio e on e.supervisor_id = s.emp_id group by s.emp_id, s.emp_name having count(*) = (select max(cnt) from (select count(*) cnt from employee_portfolio where supervisor_id is not null groupby supervisor_id) emp_cnt );

EMP_ID EMP_NAME---------- ------------------------------1234 Terry4562 Ryan


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12. Find the employees who have worked on the same project in the most number of roles.

Code:SQL> select distinct e.emp_id, emp_name from employee_project_team pt inner

join employee_portfolioe on e.emp_id = pt.emp_id group by e.emp_id, emp_name, project_id HAVINGcount(distinct role_id) =(SELECT max(num_roles) max_roles FROM (SELECT emp_id, project_id,count(distinct role_id) num_rolesfrom employee_project_team group by emp_id, project_id) emp_roles);

EMP_ID EMP_NAME---------- ------------------------------3251 Mark

Example table

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