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+# SQL - UNIONS CLAUSE
+
+The SQL UNION clause/operator is used to combine the results of two or more SELECT statements without returning any duplicate rows.
+
+- While using this UNION clause, each SELECT statement must have:
+
+  - The same number of columns selected
+  - The same number of column expressions
+  - The same data type and
+  - Have them in the same order
+
+But they need not have to be in the same length.    
+
+_Example_
+
+Consider the following two tables.
+
+Table 1 − customers table is as follows:
+    
+    +----+----------+-----+-----------+----------+
+    | id | name     | age | address   | salary   |
+    +----+----------+-----+-----------+----------+
+    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
+    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
+    |  3 | kaushik  |  23 | Kota      |  2000.00 |
+    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
+    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
+    |  6 | Komal    |  22 | MP        |  4500.00 |
+    |  7 | Muffy    |  24 | Indore    | 10000.00 |
+    +----+----------+-----+-----------+----------+
+
+Table 2 − orders table is as follows:
+
+    +-----+---------------------+-------------+--------+
+    | oid | date                | customer_id | amount |
+    +-----+---------------------+-------------+--------+
+    | 102 | 2009-10-08 00:00:00 |           3 |   3000 |
+    | 100 | 2009-10-08 00:00:00 |           3 |   1500 |
+    | 101 | 2009-11-20 00:00:00 |           2 |   1560 |
+    | 103 | 2008-05-20 00:00:00 |           4 |   2060 |
+    +-----+---------------------+-------------+--------+
+
+Now, let us join these two tables in our SELECT statement as follows:
+
+```sql
+SELECT id, name, amount, date
+   FROM customer
+   LEFT JOIN orders
+   ON customers.id = orders.customer_id
+UNION
+   SELECT id, name, amount, date
+   FROM customer
+   RIGHT JOIN orders
+   ON customers.id = orders.customer_id
+```
+
+This would produce the following result:
+
+### The UNION ALL Clause
+The UNION ALL operator is used to combine the results of two SELECT statements including duplicate rows.
+
+The same rules that apply to the UNION clause will apply to the UNION ALL operator.
+
+_Example_ - 
+Consider the following two tables:
+
+* Table 1 − customers table is as follows:
+ 
+      +----+----------+-----+-----------+----------+
+      | id | name     | age | address   | salary   |
+      +----+----------+-----+-----------+----------+
+      |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
+      |  2 | Khilan   |  25 | Delhi     |  1500.00 |
+      |  3 | kaushik  |  23 | Kota      |  2000.00 |
+      |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
+      |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
+      |  6 | Komal    |  22 | MP        |  4500.00 |
+      |  7 | Muffy    |  24 | Indore    | 10000.00 |
+      +----+----------+-----+-----------+----------+
+
+* Table 2 − orders table is as follows:
+
+      +-----+---------------------+-------------+--------+
+      | oid | date                | customer_id | amount |
+      +-----+---------------------+-------------+--------+
+      | 102 | 2009-10-08 00:00:00 |           3 |   3000 |
+      | 100 | 2009-10-08 00:00:00 |           3 |   1500 |
+      | 101 | 2009-11-20 00:00:00 |           2 |   1560 |
+      | 103 | 2008-05-20 00:00:00 |           4 |   2060 |
+      +-----+---------------------+-------------+--------+
+
+Now, let us join these two tables in our SELECT statement as follows :
+```sql
+SELECT id, name, amount, date
+   FROM customers
+   LEFT JOIN orders
+   ON customers.id = order.customer_id
+UNION ALL
+   SELECT id, name, amount, date
+   FROM customers
+   RIGHT JOIN orders
+   ON customers.id = orders.customer_id;
+```
+
+This would produce the following result:
+    
+    +------+----------+--------+---------------------+
+    | id   | name     | amount | date                |
+    +------+----------+--------+---------------------+
+    |    1 | Ramesh   |   NULL | NULL                |
+    |    2 | Khilan   |   1560 | 2009-11-20 00:00:00 |
+    |    3 | kaushik  |   3000 | 2009-10-08 00:00:00 |
+    |    3 | kaushik  |   1500 | 2009-10-08 00:00:00 |
+    |    4 | Chaitali |   2060 | 2008-05-20 00:00:00 |
+    |    5 | Hardik   |   NULL | NULL                |
+    |    6 | Komal    |   NULL | NULL                |
+    |    7 | Muffy    |   NULL | NULL                |
+    |    3 | kaushik  |   3000 | 2009-10-08 00:00:00 |
+    |    3 | kaushik  |   1500 | 2009-10-08 00:00:00 |
+    |    2 | Khilan   |   1560 | 2009-11-20 00:00:00 |
+    |    4 | Chaitali |   2060 | 2008-05-20 00:00:00 |
+    +------+----------+--------+---------------------+
+
+Note : **There are two other clauses (i.e., operators), which are like the UNION clause.**