SQL Advanced (2)

The INNER join keyword returns rows when the SQL Advanced (2) SQL INNER join keyword has at least one match in the table.
INNER JOIN keyword Syntax

SELECT column_name (s) from Table_name1inner JOIN table_name2 on Table_name1.column_name=table_name2.column_name

Note: INNER join is the same as join.
The original table (used in the example):
"Persons" table:
City

id_p	LastName	FirstName	Address
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

"Orders" table:

Id_o	OrderNo	id_p
1	77895	3
2	44678	3
3	22456	1
4	24562	1
5	34764	65

INNER JOIN (INNER join) instance now we want to list everyone's orders.
You can use the following SELECT statement:

SELECT Persons.lastname, Persons.firstname, Orders.ordernofrom personsinner JOIN Orderson persons.id_p=orders.id_ Porder by Persons.lastname

Result set:

LastName	FirstName	OrderNo
Adams	John	22456
Adams	John	24562
Carter	Thomas	77895
Carter	Thomas	44678

The INNER JOIN keyword returns a row when there is at least one match in the table. If the rows in "Persons" do not match in "Orders," the rows are not listed.
The SQL LEFT JOIN keyword, the table_name1, is returned for all rows, even if there are no matching rows in the right table (table_name2).
Left JOIN keyword syntax

SELECT column_name (s) from Table_name1left JOIN table_name2 on Table_name1.column_name=table_name2.column_name

Note: In some databases, the left join is called the left OUTER join.
The original table (used in the example):
"Persons" table:
City

id_p	LastName	FirstName	Address
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

"Orders" table:

Id_o	OrderNo	id_p
1	77895	3
2	44678	3
3	22456	1
4	24562	1
5	34764	65

Left join (left JOIN) instance now, we want to list all the people and their orders-if any.
You can use the following SELECT statement:

SELECT Persons.lastname, Persons.firstname, Orders.ordernofrom personsleft JOIN Orderson persons.id_p=orders.id_ Porder by Persons.lastname

Result set:

LastName	FirstName	OrderNo
Adams	John	22456
Adams	John	24562
Carter	Thomas	77895
Carter	Thomas	44678
Bush	George

The left JOIN keyword returns all rows from the table (Persons), even if there are no matching rows in the right table (Orders).
SQL Right JOIN keyword
The right join keyword in the "r" keyword will return all rows in the table (table_name2), even if there are no matching rows in the left table (table_name1).
Right JOIN keyword syntax

SELECT column_name (s) from Table_name1right JOIN table_name2 on Table_name1.column_name=table_name2.column_name

Note: In some databases, the right join is called a OUTER join.
The original table (used in the example):
"Persons" table:
City

id_p	LastName	FirstName	Address
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

"Orders" table:

Id_o	OrderNo	id_p
1	77895	3
2	44678	3
3	22456	1
4	24562	1
5	34764	65

Right Join instance now we want to list all the orders and the people who ordered them-if any.
You can use the following SELECT statement:

SELECT Persons.lastname, Persons.firstname, Orders.ordernofrom personsright JOIN Orderson persons.id_p=orders.id_ Porder by Persons.lastname

Result set:

LastName	FirstName	OrderNo
Adams	John	22456
Adams	John	24562
Carter	Thomas	77895
Carter	Thomas	44678
		34764

The right JOIN keyword returns all of the rows from the table (Orders), even if there are no matching rows in the left table (Persons).
SQL full join keyword SQL full join keyword The full join keyword returns a row as long as there is a match in one of the tables.
Full JOIN keyword syntax

SELECT column_name (s) from Table_name1full JOIN table_name2 on Table_name1.column_name=table_name2.column_name

Note: In some databases, full join is called full OUTER join.
The original table (used in the example):
"Persons" table:
City

id_p	LastName	FirstName	Address
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

"Orders" table:

Id_o	OrderNo	id_p
1	77895	3
2	44678	3
3	22456	1
4	24562	1
5	34764	65

Full join instances now we want to list all the people, their orders, all the orders, and the people who ordered them.
You can use the following SELECT statement:

SELECT Persons.lastname, Persons.firstname, Orders.ordernofrom personsfull JOIN Orderson persons.id_p=orders.id_ Porder by Persons.lastname

Result set:

LastName	FirstName	OrderNo
Adams	John	22456
Adams	John	24562
Carter	Thomas	77895
Carter	Thomas	44678
Bush	George
		34764

The full JOIN keyword returns all rows from the left table (Persons) and the right table (Orders). If the rows in "Persons" do not match in the table "orders", or if the rows in "orders" do not have a match in the table "Persons", the rows are also listed.
The SQL union and UNION ALL operator SQL UNION operator UNION operator is used to combine the result set of two or more SELECT statements.
Note that the SELECT statement inside the UNION must have the same number of columns. The column must also have a similar data type. Also, the order of the columns in each SELECT statement must be the same.
SQL UNION Syntax

SELECT column_name (s) from Table_name1unionselect column_name (s) from table_name2

Note: By default, the UNION operator chooses a different value. If duplicate values are allowed, use UNION all.
SQL UNION All syntax

SELECT column_name (s) from Table_name1union Allselect column_name (s) from table_name2

In addition, the column name in the union result set is always equal to the column name in the first SELECT statement in the Union.
The original table is used in the following example:
Employees_china:

e_id	E_name
01	Zhang, Hua
02	Wang, Wei
03	Carter, Thomas.
04	Yang, Ming

Employees_usa:

e_id	E_name
01	Adams, John.
02	Bush, George.
03	Carter, Thomas.
04	Gates, Bill.

Use the UNION command instance to list all the different employee names in China and the United States:

SELECT E_name from Employees_chinaunionselect e_name from Employees_usa

Results

E_name
Zhang, Hua
Wang, Wei
Carter, Thomas.
Yang, Ming
Adams, John.
Bush, George.
Gates, Bill.

Note: This command cannot list all employees in China and the United States. In the above example, we have two employees of the same name, and only one of them is listed. The UNION command will only pick a different value.
The UNION ALL UNION ALL command is almost equivalent to the Union command, but the union ALL command lists all values.

SQL Statement 1UNION allsql Statement 2

Use the UNION all command
Example: List of all employees in China and the United States:

SELECT e_name from Employees_chinaunion allselect e_name from Employees_usa

Results

E_name
Zhang, Hua
Wang, Wei
Carter, Thomas.
Yang, Ming
Adams, John.
Bush, George.
Carter, Thomas.
Gates, Bill.

SQL Advanced (2)