FOREIGN KEY
FOREIGN is column in a table that is the primary key
column in another table. a table can
have multiple foreign column in a table .
It can hold multiple null values.
Example: Below are the EMPLOYEE
and EMPSALARY table.
EMPLOYEE table:
CREATE TABLE EMPLOYEE(
ID
INT NOT
NULL,
NAME VARCHAR (20) NOT NULL,
AGE
INT NOT
NULL,
ADDRESS CHAR (25) ,
SALARY
DECIMAL (18, 2),
CONSTRAINT
pk_EmployeeID PRIMARY KEY
(ID)
);
EMPSALARY table:
CREATE TABLE EMPSALARY (
ID INT NOT NULL,
DATE DATETIME,
EMPLOYEE_ID INT
references EMPLOYEE(ID),
AMOUNT double,
CONSTRAINT
pk_ EMPSALARYID PRIMARY KEY (ID)
);
in above EMPSALARY table EMPLOYEE_ID is the foreign
key that refrenece to the primary key in the EMPLOYEE table.
More SQL Constraints
More SQL Constraints
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