UNION does not return duplicate results (similar to the DISTINCT keyword). : Union « Select Clause « SQL / MySQL






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  2. Select Clause
  3. Union

UNION does not return duplicate results (similar to the DISTINCT keyword).

   
mysql>
You can override this by specifying that all results must be returned with the ALL keyword:
mysql>
mysql> CREATE TABLE customer (
    ->   id int(11) default NULL,
    ->   first_name varchar(30) default NULL,
    ->   surname varchar(40) default NULL
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO customer VALUES (1, 'Tom', 'Clegg');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO customer VALUES (2, 'Jack', 'Smith');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO customer VALUES (3, 'Will', 'Powers');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO customer VALUES (4, 'Peter', 'Miller');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> CREATE TABLE sales (
    ->   code int(11) default NULL,
    ->   sales_rep int(11) default NULL,
    ->   customer int(11) default NULL,
    ->   value int(11) default NULL
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO sales VALUES (1, 1, 1, 2000);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales VALUES (2, 4, 3, 250);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales VALUES (3, 2, 3, 500);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales VALUES (4, 1, 4, 450);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales VALUES (5, 3, 1, 3800);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales VALUES (6, 1, 2, 500);
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> CREATE TABLE sales_rep (
    ->   employee_number int(11) default NULL,
    ->   surname varchar(40) default NULL,
    ->   first_name varchar(30) default NULL,
    ->   commission tinyint(4) default NULL,
    ->   date_joined date default NULL,
    ->   birthday date default NULL
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO sales_rep VALUES (1, 'Ray', 'Sol', 10,  '2000-02-15', '1976-03-18');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales_rep VALUES (2, 'Goal', 'Charlene', 15, '1998-07-09', '1958-11-30');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales_rep VALUES (3, 'Soy', 'Mike', 10, '2001-05-14', '1971-06-18');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO sales_rep VALUES (4, 'Ray', 'Mongane', 10, '2002-11-23', '1982-01-04');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> CREATE TABLE old_customer(id int, first_name varchar(30), surname varchar(40));
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO old_customer VALUES (5432, 'Thulani', 'Salie'), (2342, 'Shahiem', 'Papo');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql>
mysql> SELECT id, first_name, surname FROM old_customer UNION SELECT
    ->  id, first_name,surname FROM customer;
+------+------------+---------+
| id   | first_name | surname |
+------+------------+---------+
| 5432 | Thulani    | Salie   |
| 2342 | Shahiem    | Papo    |
|    1 | Tom        | Clegg   |
|    2 | Jack       | Smith   |
|    3 | Will       | Powers  |
|    4 | Peter      | Miller  |
+------+------------+---------+
6 rows in set (0.00 sec)

mysql>
mysql>
mysql>
mysql> drop table sales;
Query OK, 0 rows affected (0.00 sec)

mysql> drop table customer;
Query OK, 0 rows affected (0.00 sec)

mysql> drop table sales_rep;
Query OK, 0 rows affected (0.00 sec)

mysql> drop table old_customer;
Query OK, 0 rows affected (0.00 sec)

mysql>








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