How Does Full Join Work in SQL?

Question

I am tring to create a new table into the database if the table name given is not present in database using Php .
This is the code that I am using .

  $conn = mysql_connect($dbhost, $dbuser, $dbpass);
    if(!$conn)
    {
            die('Failed to connect to server: ' . mysql_error());
            exit;
    }
    $db_selected = mysql_select_db($dbname);
    if(!$db_selected)
    {
           $db_selected = " CREATE DATABASE $dbname ";
    }
    $usertb1 = mysql_query("select 1 from $usertb LIMIT 1");
    if( $usertb1 !== FALSE )
    {
           $sql = "CREATE TABLE IF NOT EXISTS $usertb ( uid INT(20) AUTO_INCREMENT UNIQUE KEY NOT NULL,name VARCHAR(40),email varchar(40) PRIMARY KEY NOT NULL)";
    }
    $typetb1 = mysql_query("select 1 from $typetb LIMIT 1");
    if( $typetb1 !== FALSE)
    {
           $sql1 = "CREATE TABLE IF NOT EXISTS $typetb( uid INT(20) NOT NULL, type ENUM('WEB','APP','CART') NOT NULL ,unsubscribe TINYINT(1) NOT NULL,bounce TINYINT(1) NOT NULL,complaint TINYINT(1) NOT NULL, PRIMARY KEY (uid,type), FOREIGN KEY(uid) WHERE promo_user(uid))";
    }

Answer 1

The FULL OUTER JOIN keyword combines the result of both LEFT and RIGHT joins.

Its syntax is as follows:
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;

The FULL OUTER JOIN keyword will return all the rows from the left table and all the rows from the right table . If there are rows in table1 that do not have matches in table2 , or if there are rows in table2 that do not have matches in table1 , those rows will be listed as well(as Null).

Answer 2

SELECT * FROM Employee AS E FULL OUTER JOIN Category AS C ON E.EmployeeID=C.CategoryID

Comments

need some explanation it should be use....