CSED421 Database Systems Lab Join. Human Resources (HR) schema.

CSED421Database Systems Lab

Join

Human Resources (HR) schema

Cross Join (Cartesian Prod-uct)

107×27=2889 rows selected.

employees departments

27 rows selected.107 rows selected.

SELECT e.last_name, d.department_nameFROM employees e, departments d;

…

Inner JoinEMPLOYEES DEPARTMENTS

106 rows selected.

27 rows selected.107 rows selected.

SELECT e.last_name, d.department_nameFROM employees e, departments dWHERE e.department_id = d.department_id;

…

Use a join to query data from more than one table.

The join condition in the WHERE clause. mysql> SELECT table1.column1, table2.column2

–> FROM table1, table2 –> WHERE table1.column3 = table2.column3 -> AND table1.column4 = table2.column4;

JOIN ~ ON ~ mysql> SELECT table1.column1, table2.column2

–> FROM table1 JOIN table2 –> ON table1.column3 = table2.column3 -> AND table1.column4 = table2.column4;

JOIN ~ USING ~ mysql> SELECT table1.column1, table2.column2

–> FROM table1 JOIN table2 –> USING (column3, column4);

Inner Join

Equijoin

107 rows selected.

EMPLOYEES DEPARTMENTS

27 rows selected.

(Foreign key)

(Primary key)

SELECT e.employee_id, d.department_id, d.department_nameFROM employees e, departments dWHERE e.department_id = d.department_id;

Non-Equijoin

107 rows selected.

EMPLOYEES JOB_GRADES

6 rows selected.

107 rows selected.

SELECT last_name, salary, grade_levelFROM employees, job_gradesWHERE salary BETWEEN lowest_sal AND highest_sal;

(WHERE salary >= lowest_sal AND salary <= highest_sal)

…

Joining More than Two Ta-bles

107 rows selected.

EMPLOYEES DEPARTMENTS

27 rows selected.

23 rows selected.

LOCATIONS

SELECT e.employee_id, d.department_id, l.cityFROM employees e, departments d, locations lWHERE e.department_id = d.department_id AND d.location_id = l.location_id;

Outer Join

107 rows selected.

EMPLOYEES DEPARTMENTS

27 rows selected.

Left join All rows from the left table, even if there are no

matches in the right table. mysql> SELECT table1.column1, table2.column2 –> FROM table1 LEFT JOIN table2 –> ON table1.column3 = table2.column3;

Right join All rows from the right table, even if there are no

matches in the left table. mysql> SELECT table1.column1, table2.column2 –> FROM table1 RIGHT JOIN table2 –> ON table1.column3 = table2.column3;

Outer Join

Outer Join

SELECT employee_id, department_nameFROM employees e LEFT JOIN departments dON e.department_id = d.department_id;

EMPLOYEESDEPARTMENTS

107 rows selected. 107 rows selected.

EMP ⋈ DEPT

27 rows selected.

Outer Join

SELECT employee_id, department_nameFROM employees e JOIN departments dON e.department_id = d.department_id;

EMPLOYEESDEPARTMENTS

107 rows selected. 106 rows selected.

EMP ⋈ DEPT

27 rows selected.

Self Join

8 rows selected.

107 rows selected.

EMPLOYEES (WORKER) EMPLOYEES (MANAGER)

SELECT e1.last_name, e2.last_nameFROM employees e1, employees e2WHERE e1.employee_id = e2.manager_id;

106 rows selected.

SELECT table1.column, table2.columnFROMtable1[ CROSS JOIN table2 ] |[ NATURAL JOIN table2 ] |[ JOIN table2 USING (column_name)] |[ JOIN table2

ON (table1.column1 = table2.column2) ] |[ LEFT | RIGHT | FULL OUTER JOIN table2

ON (table1.column1 = table2.column2) ];

Joining Tables Using SQL: 1999 Syntax

Source hr.sql

http://ids.postech.ac.kr/dblab/2014/hr.sql

Human Resources (HR) schema

lab3 DB schema

1. 특정 부서에 소속되어 있는 직원들의 이름 (last_name) 과 각 직원의 소속부서의 이름 (department_name) 을 출력하기 .

Practice

106 rows selected.

…

2. 부서 이름 (department_name) 과 해당 부서가 위치한 국가 이름(country_name), 지역 이름 (region_name) 을 출력하기 .

Practice

27 rows selected.

3. ‘Seattle’ 도시 (city) 에서 근무하는 직원들의 부서명(department_name) 과 이름 (last_name) 을 출력하기 .

Practice

4. 모든 부서이름 (department_name) 과 각 부서에 소속된 직원의 수 출력하기 .

Practice

27 rows selected.

5. 자신의 상사 (manager) 보다 오래 일한 직원들의 이름(last_name) 을 출력하기 .

Practice