MySQL Tutorial/Table Join/NATURAL LEFT JOIN
NATURAL LEFT JOIN
The NATURAL LEFT JOIN is the same as a regular LEFT JOIN.
The NATURAL LEFT JOIN automatically uses all the matching columns as part of the join.
The NATURAL LEFT JOIN is syntactically equivalent to a LEFT JOIN with a USING clause that names all the identical columns of the two tables.
The syntax looks like the following:
mysql>
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 (0.03 sec)
mysql>
mysql> create table job (
-> id int,
-> title VARCHAR(20)
-> );
Query OK, 0 rows affected (0.05 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 (0.00 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 (0.00 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 (0.02 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>
mysql> SELECT C.First_Name, C.Last_Name, O.title
-> FROM Employee as C
-> NATURAL LEFT JOIN JOb as O;
+------------+-----------+------------+
| 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> 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>
This would return all the rows from the Employee table, regardless of whether they had a matching record in any of the same columns of the Job table.
The Job table would return a NULL if it did not have a match.
mysql>
NATURAL LEFT JOIN across three tables
mysql>
mysql> CREATE TABLE Books(
-> BookID SMALLINT NOT NULL PRIMARY KEY,
-> BookTitle VARCHAR(60) NOT NULL,
-> Copyright YEAR NOT NULL
-> )
-> ENGINE=INNODB;
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql>
mysql> INSERT INTO Books VALUES (12786, "Java", 1934),
-> (13331, "MySQL", 1919),
-> (14356, "PHP", 1966),
-> (15729, "PERL", 1932),
-> (16284, "Oracle", 1996),
-> (17695, "Pl/SQL", 1980),
-> (19264, "JavaScript", 1992),
-> (19354, "www.sqle.ru", 1993);
Query OK, 8 rows affected (0.03 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> CREATE TABLE Authors(
-> AuthID SMALLINT NOT NULL PRIMARY KEY,
-> AuthFN VARCHAR(20),
-> AuthMN VARCHAR(20),
-> AuthLN VARCHAR(20)
-> )
-> ENGINE=INNODB;
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql>
mysql> INSERT INTO Authors VALUES (1006, "H", "S.", "T"),
-> (1007, "J", "C", "O"),
-> (1008, "B", NULL, "E"),
-> (1009, "R", "M", "R"),
-> (1010, "J", "K", "T"),
-> (1011, "J", "G.", "N"),
-> (1012, "A", NULL, "P"),
-> (1013, "A", NULL, "W"),
-> (1014, "N", NULL, "A");
Query OK, 9 rows affected (0.05 sec)
Records: 9 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> CREATE TABLE AuthorBook(
-> AuthID SMALLINT NOT NULL,
-> BookID SMALLINT NOT NULL,
-> PRIMARY KEY (AuthID, BookID),
-> FOREIGN KEY (AuthID) REFERENCES Authors (AuthID),
-> FOREIGN KEY (BookID) REFERENCES Books (BookID)
-> )
-> ENGINE=INNODB;
Query OK, 0 rows affected (0.05 sec)
mysql>
mysql>
mysql> INSERT INTO AuthorBook VALUES (1006, 14356),
-> (1008, 15729),
-> (1009, 12786),
-> (1010, 17695),
-> (1011, 15729),
-> (1012, 19264),
-> (1012, 19354),
-> (1014, 16284);
Query OK, 8 rows affected (0.05 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> select * from Authors;
+--------+--------+--------+--------+
| AuthID | AuthFN | AuthMN | AuthLN |
+--------+--------+--------+--------+
| 1006 | H | S. | T |
| 1007 | J | C | O |
| 1008 | B | NULL | E |
| 1009 | R | M | R |
| 1010 | J | K | T |
| 1011 | J | G. | N |
| 1012 | A | NULL | P |
| 1013 | A | NULL | W |
| 1014 | N | NULL | A |
+--------+--------+--------+--------+
9 rows in set (0.01 sec)
mysql> select * from Books;
+--------+----------------+-----------+
| BookID | BookTitle | Copyright |
+--------+----------------+-----------+
| 12786 | Java | 1934 |
| 13331 | MySQL | 1919 |
| 14356 | PHP | 1966 |
| 15729 | PERL | 1932 |
| 16284 | Oracle | 1996 |
| 17695 | Pl/SQL | 1980 |
| 19264 | JavaScript | 1992 |
| 19354 | www.sqle.ru | 1993 |
+--------+----------------+-----------+
8 rows in set (0.00 sec)
mysql> select * from AuthorBook;
+--------+--------+
| AuthID | BookID |
+--------+--------+
| 1009 | 12786 |
| 1006 | 14356 |
| 1008 | 15729 |
| 1011 | 15729 |
| 1014 | 16284 |
| 1010 | 17695 |
| 1012 | 19264 |
| 1012 | 19354 |
+--------+--------+
8 rows in set (0.00 sec)
mysql>
mysql> SELECT BookTitle, Copyright,
-> CONCAT_WS(" ", AuthFN, AuthMN, AuthLN) AS Author
-> FROM Books AS b NATURAL LEFT JOIN AuthorBook AS ab
-> NATURAL LEFT JOIN Authors AS a
-> WHERE Copyright<1980
-> ORDER BY BookTitle;
+-----------+-----------+--------+
| BookTitle | Copyright | Author |
+-----------+-----------+--------+
| Java | 1934 | R M R |
| MySQL | 1919 | |
| PERL | 1932 | B E |
| PERL | 1932 | J G. N |
| PHP | 1966 | H S. T |
+-----------+-----------+--------+
5 rows in set (0.00 sec)
mysql>
mysql> drop table AuthorBook;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table Books;
Query OK, 0 rows affected (0.03 sec)
mysql> drop table Authors;
Query OK, 0 rows affected (0.05 sec)