A LEFT JOIN returns all rows from the left table in a join.
All the rows from the table on the left side of the equation will be returned, regardless of whether they have a match with the table on the right side.
If there is no match, a NULL value will be returned.
mysql>
mysql> CREATE TABLE Employee(
-> id int,
-> first_name VARCHAR(15),
-> last_name VARCHAR(15),
-> start_date DATE,
-> end_date DATE,
-> salary FLOAT(8,2),
-> city VARCHAR(10),
-> description VARCHAR(15)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql> create table job (
-> id int,
-> title VARCHAR(20)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values (1,'Jason', 'Martin', '19960725', '20060725', 1234.56, 'Toronto', 'Programmer');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(2,'Alison', 'Mathews', '19760321', '19860221', 6661.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.02 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(3,'James', 'Smith', '19781212', '19900315', 6544.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(4,'Celia', 'Rice', '19821024', '19990421', 2344.78, 'Vancouver','Manager');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(5,'Robert', 'Black', '19840115', '19980808', 2334.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(6,'Linda', 'Green', '19870730', '19960104', 4322.78,'New York', 'Tester');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(7,'David', 'Larry', '19901231', '19980212', 7897.78,'New York', 'Manager');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(8,'James', 'Cat', '19960917', '20020415', 1232.78,'Vancouver', 'Tester');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into job (id, title) values (1,'Tester');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (2,'Accountant');
Query OK, 1 row affected (0.02 sec)
mysql> insert into job (id, title) values (3,'Developer');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (4,'Coder');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (5,'Director');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (6,'Mediator');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (7,'Proffessor');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (8,'Programmer');
Query OK, 1 row affected (0.00 sec)
mysql> insert into job (id, title) values (9,'Developer');
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> select * from job;
+------+------------+
| id | title |
+------+------------+
| 1 | Tester |
| 2 | Accountant |
| 3 | Developer |
| 4 | Coder |
| 5 | Director |
| 6 | Mediator |
| 7 | Proffessor |
| 8 | Programmer |
| 9 | Developer |
+------+------------+
9 rows in set (0.00 sec)
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| id | first_name | last_name | start_date | end_date | salary | city | description |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer |
| 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester |
| 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester |
| 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager |
| 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester |
| 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester |
| 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager |
| 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
8 rows in set (0.00 sec)
mysql>
mysql>
mysql> SELECT C.First_Name, C.Last_Name, O.title
-> FROM Employee as C
-> LEFT JOIN job as O ON C.ID = O.ID;
+------------+-----------+------------+
| First_Name | Last_Name | title |
+------------+-----------+------------+
| Jason | Martin | Tester |
| Alison | Mathews | Accountant |
| James | Smith | Developer |
| Celia | Rice | Coder |
| Robert | Black | Director |
| Linda | Green | Mediator |
| David | Larry | Proffessor |
| James | Cat | Programmer |
+------------+-----------+------------+
8 rows in set (0.00 sec)
mysql>
The old way:
mysql>
mysql> SELECT C.First_Name, C.Last_Name, O.title
-> FROM Employee AS C, job as O
-> WHERE C.ID = O.ID;
+------------+-----------+------------+
| First_Name | Last_Name | title |
+------------+-----------+------------+
| Jason | Martin | Tester |
| Alison | Mathews | Accountant |
| James | Smith | Developer |
| Celia | Rice | Coder |
| Robert | Black | Director |
| Linda | Green | Mediator |
| David | Larry | Proffessor |
| James | Cat | Programmer |
+------------+-----------+------------+
8 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql>
mysql>
mysql> drop table job;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql>