How can I SELECT multiple values from 2 tables? SQL Developer - sql

Question

I want to SELECT STAFF_ID, STAFF_NAME and PROJECT_ID. STAFF_ID and PROJECT_ID are linked in a table ASSIGNMENTS, but I want to show that link while also showing the STAFF_NAME for each STAFF_ID from the STAFF table. Here is my code:
CREATE TABLE PROJECT
(PROJECT_ID CHAR(5) NOT NULL,
PROJECT_NAME CHAR(20),
PROJECT_TYPE CHAR(20),
START_DATE DATE,
END_DATE DATE,
PRIMARY KEY (PROJECT_ID));
CREATE TABLE STAFF
(STAFF_ID CHAR(5) NOT NULL,
STAFF_NAME CHAR(20),
JOB_TYPE CHAR(20),
JOB_GRADE CHAR(20),
PRIMARY KEY (STAFF_ID));
CREATE TABLE ASSIGNMENTS
(ASSIGNMENT_ID CHAR(5) NOT NULL,
PROJECT_ID CHAR(5),
STAFF_ID CHAR(5),
PRIMARY KEY (ASSIGNMENT_ID),
FOREIGN KEY (PROJECT_ID) REFERENCES PROJECT(PROJECT_ID),
FOREIGN KEY (STAFF_ID) REFERENCES STAFF(STAFF_ID));
All the tables have been populated with data, and this is the query I've used so far which shows which employees work on a given project (but only with STAFF_ID, not with STAFF_NAME included):
SELECT STAFF_ID, PROJECT_ID
FROM ASSIGNMENTS
WHERE PROJECT_ID = 'B0005';
How can I show the links like this while also including the STAFF_NAME linked to the STAFF_ID from the STAFF table?
Here is some data for a row of each table:
INSERT INTO PROJECT (PROJECT_ID, PROJECT_NAME, PROJECT_TYPE, START_DATE, END_DATE)
VALUES ('B0001','BIKESHOP.COM','WEB DEVELOPMENT',TO_DATE('15/01/17','DD/MM/YY'),TO_DATE('15/02/17','DD/MM/YY'));
INSERT INTO STAFF (STAFF_ID, STAFF_NAME, JOB_TYPE, JOB_GRADE)
VALUES ('ST001','JOHN MASON','WEB DEVELOPER','1');
INSERT INTO ASSIGNMENTS (ASSIGNMENT_ID, PROJECT_ID, STAFF_ID, HARDWARE_ID, SOFTWARE_ID)
VALUES ('A0001','B0001','ST001','H0001','S0001');
What I want to show is PROJECT_ID, STAFF_ID, STAFF_NAME. Just three columns showing those 3 values.

Answer 1

You just need to add join to STAFF table. Something like this
SELECT STAFF.STAFF_ID, STAFF.STAFF_NAME, ASSIGNMENTS.PROJECT_ID
FROM ASSIGNMENTS
INNER JOIN STAFF ON ASSIGNMENTS.STAFF_ID = STAFF.STAFF_ID
WHERE ASSIGNMENTS.PROJECT_ID = 'B0005';

Answer 2

i think this select can solve your problem
select PROJECT_ID, STAFF_ID, STAFF_NAME from ASSIGNMENTS
inner join STAFF on STAFF.STAFF_ID=ASSIGNMENTS.STAFF_ID

Answer 3

For achieving this need, Join the three tables as next approach:
Generic Syntax:
select *
from
tableA a
inner join
tableB b
on a.common = b.common
inner join
TableC c
on b.common = c.common
so follow the next query:
select a.PROJECT_ID, b.STAFF_ID, c.STAFF_NAME
from PROJECT a inner join ASSIGNMENTS b
on a.PROJECT_ID = b.PROJECT_ID
inner join STAFF c
on c.STAFF_ID = b.STAFF_ID
Result: