MySQL Tutorial/Table Join/Left Join

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Версия от 09:53, 26 мая 2010; Admin (обсуждение | вклад) (1 версия)
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Add a WHERE clause to restrict the output

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>
mysql> create table duty (
    ->   id         int,
    ->   task       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 (0.01 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> insert into duty (id, task) values (1,"Test");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (2,"Calculate");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (3,"Program");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (4,"Test");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (5,"Manage");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (6,"Talk");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values  (7,"Speak");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (8,"Shout");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values  (9,"Walk");
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> select * from duty;
+------+-----------+
| id   | task      |
+------+-----------+
|    1 | Test      |
|    2 | Calculate |
|    3 | Program   |
|    4 | Test      |
|    5 | Manage    |
|    6 | Talk      |
|    7 | Speak     |
|    8 | Shout     |
|    9 | Walk      |
+------+-----------+
9 rows in set (0.02 sec)
mysql>
mysql>
mysql>
mysql>
mysql>
mysql> SELECT employee.first_name, job.title, duty.task
    -> FROM employee
    -> LEFT JOIN job
    -> ON employee.ID = job.ID
    -> LEFT JOIN duty
    -> ON employee.ID = duty.ID
    -> WHERE (job.title = "Coder");
+------------+-------+------+
| first_name | title | task |
+------------+-------+------+
| Celia      | Coder | Test |
+------------+-------+------+
1 row in set (0.00 sec)
mysql>
mysql>
mysql>
mysql> drop table duty;
Query OK, 0 rows affected (0.00 sec)
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>


Adding a WHERE Clause to the left Join

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> SELECT employee.first_name, employee.city, job.title
    -> FROM employee
    -> LEFT JOIN job
    -> ON employee.ID = job.ID
    -> WHERE job.title = "Coder";
+------------+-----------+-------+
| first_name | city      | title |
+------------+-----------+-------+
| Celia      | Vancouver | Coder |
+------------+-----------+-------+
1 row in set (0.00 sec)
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>


Left Join more than two tables

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 (0.01 sec)
mysql>
mysql> create table job (
    ->   id         int,
    ->   title      VARCHAR(20)
    -> );
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql>
mysql> create table duty (
    ->   id         int,
    ->   task       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 (0.01 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 (0.01 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> insert into duty (id, task) values (1,"Test");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (2,"Calculate");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (3,"Program");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (4,"Test");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (5,"Manage");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (6,"Talk");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values  (7,"Speak");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values (8,"Shout");
Query OK, 1 row affected (0.00 sec)
mysql> insert into duty (id, task) values  (9,"Walk");
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> select * from duty;
+------+-----------+
| id   | task      |
+------+-----------+
|    1 | Test      |
|    2 | Calculate |
|    3 | Program   |
|    4 | Test      |
|    5 | Manage    |
|    6 | Talk      |
|    7 | Speak     |
|    8 | Shout     |
|    9 | Walk      |
+------+-----------+
9 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql> SELECT  employee.first_name, job.title, duty.task
    -> FROM employee
    -> LEFT JOIN job
    -> ON employee.ID = job.ID
    -> LEFT JOIN duty
    -> ON employee.ID = duty.ID;
+------------+------------+-----------+
| first_name | title      | task      |
+------------+------------+-----------+
| Jason      | Tester     | Test      |
| Alison     | Accountant | Calculate |
| James      | Developer  | Program   |
| Celia      | Coder      | Test      |
| Robert     | Director   | Manage    |
| Linda      | Mediator   | Talk      |
| David      | Proffessor | Speak     |
| James      | Programmer | Shout     |
+------------+------------+-----------+
8 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql> drop table duty;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table job;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table Employee;
Query OK, 0 rows affected (0.01 sec)
mysql>
mysql>


LEFT Joins one table with itself

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 (0.05 sec)
mysql>
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 (0.01 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> 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>
mysql> SELECT s1.id, s1.first_name, s1.salary
    -> FROM employee s1
    -> LEFT JOIN employee s2 ON s1.city = s2.city AND s1.salary < s2.salary;
+------+------------+---------+
| id   | first_name | salary  |
+------+------------+---------+
|    1 | Jason      | 1234.56 |
|    2 | Alison     | 6661.78 |
|    3 | James      | 6544.78 |
|    4 | Celia      | 2344.78 |
|    4 | Celia      | 2344.78 |
|    5 | Robert     | 2334.78 |
|    5 | Robert     | 2334.78 |
|    5 | Robert     | 2334.78 |
|    6 | Linda      | 4322.78 |
|    7 | David      | 7897.78 |
|    8 | James      | 1232.78 |
|    8 | James      | 1232.78 |
|    8 | James      | 1232.78 |
|    8 | James      | 1232.78 |
+------+------------+---------+
14 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.02 sec)
mysql>


LEFT JOIN with order by

mysql>
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 (0.05 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 (0.06 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 (0.03 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 (0.11 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 (0.03 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 (0.00 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, AuthID
    -> FROM Books AS b LEFT JOIN AuthorBook AS ab
    ->    ON b.BookID=ab.BookID
    -> ORDER BY BookTitle;
+----------------+-----------+--------+
| BookTitle      | Copyright | AuthID |
+----------------+-----------+--------+
| Java           |      1934 |   1009 |
| JavaScript     |      1992 |   1012 |
| MySQL          |      1919 |   NULL |
| Oracle         |      1996 |   1014 |
| PERL           |      1932 |   1008 |
| PERL           |      1932 |   1011 |
| PHP            |      1966 |   1006 |
| Pl/SQL         |      1980 |   1010 |
| www.sqle.ru |      1993 |   1012 |
+----------------+-----------+--------+
9 rows in set (0.00 sec)
mysql>
mysql> drop table AuthorBook;
Query OK, 0 rows affected (0.03 sec)
mysql> drop table Books;
Query OK, 0 rows affected (0.05 sec)
mysql> drop table Authors;
Query OK, 0 rows affected (0.05 sec)


LEFT JOIN with Using

mysql>
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 (0.05 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 (0.25 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 (0.02 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 (0.27 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 (0.06 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 (0.02 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, AuthID
    -> FROM Books LEFT JOIN AuthorBook
    ->    USING (BookID)
    -> ORDER BY BookTitle;
+----------------+-----------+--------+
| BookTitle      | Copyright | AuthID |
+----------------+-----------+--------+
| Java           |      1934 |   1009 |
| JavaScript     |      1992 |   1012 |
| MySQL          |      1919 |   NULL |
| Oracle         |      1996 |   1014 |
| PERL           |      1932 |   1008 |
| PERL           |      1932 |   1011 |
| PHP            |      1966 |   1006 |
| Pl/SQL         |      1980 |   1010 |
| www.sqle.ru |      1993 |   1012 |
+----------------+-----------+--------+
9 rows in set (0.00 sec)
mysql>
mysql> drop table AuthorBook;
Query OK, 0 rows affected (0.03 sec)
mysql> drop table Books;
Query OK, 0 rows affected (0.03 sec)
mysql> drop table Authors;
Query OK, 0 rows affected (0.03 sec)


The Left Join

In left join, data from the LEFT of the join will be displayed and is where the term LEFT JOIN comes from.

Syntax:



SELECT <column_name>
FROM <Table1>
LEFT JOIN <Table2>
ON Table1.column = Table2.column


Three-Table LEFT JOIN

mysql>
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 (0.05 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 (0.05 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 (0.08 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 (0.03 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 (0.00 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 (0.01 sec)
mysql>
mysql> SELECT BookTitle, Copyright, CONCAT_WS(" ", AuthFN, AuthMN, AuthLN) AS Author
    -> FROM Books AS b LEFT JOIN AuthorBook AS ab ON b.BookID=ab.BookID
    ->    LEFT JOIN Authors AS a ON ab.AuthID=a.AuthID
    -> ORDER BY BookTitle;
+----------------+-----------+--------+
| BookTitle      | Copyright | Author |
+----------------+-----------+--------+
| Java           |      1934 | R M R  |
| JavaScript     |      1992 | A P    |
| MySQL          |      1919 |        |
| Oracle         |      1996 | N A    |
| PERL           |      1932 | B E    |
| PERL           |      1932 | J G. N |
| PHP            |      1966 | H S. T |
| Pl/SQL         |      1980 | J K T  |
| www.sqle.ru |      1993 | A P    |
+----------------+-----------+--------+
9 rows in set (0.00 sec)
mysql>
mysql> drop table AuthorBook;
Query OK, 0 rows affected (0.01 sec)
mysql> drop table Books;
Query OK, 0 rows affected (0.05 sec)
mysql> drop table Authors;
Query OK, 0 rows affected (0.05 sec)
mysql>
Источник — «http://sqle.ru/index.php?title=MySQL_Tutorial/Table_Join/Left_Join&oldid=809»