More
)
The primary key constraint uniquely identifies each record in a table.
The primary key must contain a unique value, and cannot contain a null value.
Syntax -
Mon -
Sun 8.00 AM - 8.00 PM
create table table_name (
column1_name data_type (range) not null,
column2_name data_type (range) not null,
column3_name data_type (range) not null,
………..,
primary key(column name)
);
A foreign key is a key used to link two table together.
A foreign key is a field ( or collection of field ) in one table that refer to the primary key in another table.
Example
Table 1
|
Customer_id |
Customer_name |
|
|
1 |
Nitu |
deynitu1998@gmail.com |
|
2 |
Sumit |
10sumitsarkar@gmail.com |
|
3 |
Hariom |
hariomprajapati9097@gmail.com |
Table 2
|
ORDER_ID |
ORDER_DATE |
AMOUNT |
CUSTOMER_ID |
|
1 |
'2020/5/6' |
55 |
1 |
|
2 |
'2020/06/06' |
100 |
1 |
|
3 |
'2020/03/12' |
203 |
2 |
|
4 |
'2019/05/13' |
76 |
3 |
Syntax for table 1 -
create table table_name (
column1_name not null auto increment primary key,
……………,
);
Syntax for table 2 -
create table table_name (
column1_name data_type not null auto increment primary key,
column2_name datatype (range),
…………………,
foreign key ( column_name // column name must same as table 1 primary key)
references table1_name (column name // table 1 column name which is primary key)
);Note:- Create a column with the same name as table1 primary key column name in table 2 and then put it in foreign key(column name).
Table 1
Table 2
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