Guruh talabasi Abdig’opporov javoxir Mysql 1-2-amaliy ishlar

FROM t1, t2 WHERE t1.id = t2.id; -- Use "commas" operator to join
6.2 OUTER JOIN - LEFT JOIN and RIGHT JOIN
INNER JOIN with constrain (ON or USING) produces rows that are found in both tables. On the other hand, OUTER JOIN can produce rows that are in one table, but not in another table. There are two kinds of OUTER JOINs: LEFT JOIN produces rows that are in the left table, but may not in the right table; whereas RIGHT JOIN produces rows that are in the right table but may not in the left table.
In a LEFT JOIN, when a row in the left table does not match with the right table, it is still selected but by combining with a "fake" record of all NULLs for the right table.
mysql> SELECT *
FROM t1 LEFT JOIN t2 ON t1.id = t2.id;
+----+------------+------+------------+
| id | desc | id | desc |
+----+------------+------+------------+
| 1 | ID 1 in t1 | NULL | NULL |
| 2 | ID 2 in t1 | 2 | ID 2 in t2 |
| 3 | ID 3 in t1 | 3 | ID 3 in t2 |
+----+------------+------+------------+
mysql> SELECT *
FROM t1 LEFT JOIN t2 USING (id);
+----+------------+------------+
| id | desc | desc |
+----+------------+------------+
| 1 | ID 1 in t1 | NULL |
| 2 | ID 2 in t1 | ID 2 in t2 |
| 3 | ID 3 in t1 | ID 3 in t2 |
+----+------------+------------+
mysql> SELECT *
FROM t1 RIGHT JOIN t2 ON t1.id = t2.id;
+------+------------+----+------------+
| id | desc | id | desc |
+------+------------+----+------------+
| 2 | ID 2 in t1 | 2 | ID 2 in t2 |
| 3 | ID 3 in t1 | 3 | ID 3 in t2 |
| NULL | NULL | 4 | ID 4 in t2 |
+------+------------+----+------------+
mysql> SELECT *
FROM t1 RIGHT JOIN t2 USING (id);
+----+------------+------------+
| id | desc | desc |
+----+------------+------------+
| 2 | ID 2 in t2 | ID 2 in t1 |
| 3 | ID 3 in t2 | ID 3 in t1 |
| 4 | ID 4 in t2 | NULL |
+----+------------+------------+
As the result, LEFT JOIN ensures that the result set contains every row on the left table. This is important, as in some queries, you are interested to have result on every row on the left table, with no match in the right table, e.g., searching for items without supplier. For example,
mysql> SELECT t1.id, t1.desc