SQL FOREIGN KEYin one table points to the primary key of another table .<\/p>\n
Table – users<\/p>\n
+—-+——+
\n| uid | name |
\n+—-+——+
\n| \u00a01 | AAAA |
\n| \u00a02 | BBBB |
\n| \u00a03 | CCCC |
\n| \u00a04 | DDDD |
\n| \u00a05 | EEEE |
\n+—-+——+<\/p>\n
Table \u00a0– orders<\/p>\n
+—–+—–+——–+
\n| oid | uid | items \u00a0|
\n+—–+—–+——–+
\n| \u00a0\u00a01 | \u00a0\u00a01 | Pen \u00a0\u00a0\u00a0|
\n| \u00a0\u00a02 | \u00a0\u00a02 | Watch \u00a0|
\n| \u00a0\u00a03 | \u00a0\u00a03 | shoe \u00a0\u00a0|
\n| \u00a0\u00a04 | \u00a0\u00a04 | mobile |
\n+—–+—–+——–+<\/p>\n
Here the field uid in the table orders points to the column uid in users .<\/p>\n
That is \u00a0uid in the orders is the foreign key and that in users is primary key<\/p>\n
FOREIGN KEY constraint prevent any action that may destroy the relation between the tables.<\/p>\n
It also prevent invalid data and make sure that the data to be inserted should be one of the primary key value in another<\/p>\n
Example<\/strong><\/p>\n CREATE TABLE IF NOT EXISTS `orders` ( SQL FOREIGN KEYin one table points to the primary key of another table . Table – users +—-+——+ | uid | name | +—-+——+ | \u00a01 | AAAA | | \u00a02 | BBBB | | \u00a03 | CCCC | | \u00a04 | DDDD | | \u00a05 | EEEE | +—-+——+ Table \u00a0– orders +—–+—–+——–+ | … Continue reading SQL FOREIGN KEY<\/span>
\n`oid` int(11) NOT NULL AUTO_INCREMENT,
\n`uid` int(11) NOT NULL,
\n`items` varchar(255) NOT NULL,
\nPRIMARY KEY (`oid`),
\nFOREIGN KEY (uid) REFERENCES users(uid)
\n)<\/p>\n","protected":false},"excerpt":{"rendered":"