Use of Variables : Variable « Select Clause « SQL / MySQL

1. SQL / MySQL
2. Select Clause
3. Variable

Use of Variables

       
mysql>
mysql> CREATE TABLE mytable (
    ->   id int(11) NOT NULL default '0',
    ->   choice tinyint(4) NOT NULL default '0',
    ->   ts timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
    ->   PRIMARY KEY  (id)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO mytable VALUES (1,4,'2003-01-14 15:46:18'),
    ->                                 (2,1,'2003-01-14 15:49:44'),
    ->                                 (3,4,'2003-01-14 15:49:50'),
    ->                                 (4,4,'2003-01-14 15:49:53'),
    ->                                 (5,4,'2003-01-14 15:49:54'),
    ->                                 (6,2,'2003-01-14 15:49:58');
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql>
mysql>
mysql>
mysql>
mysql> SELECT @total := COUNT(*) FROM mytable;
+--------------------+
| @total := COUNT(*) |
+--------------------+
|                  6 |
+--------------------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT choice, COUNT(*) / @total * 100 AS percentage FROM mytable GROUP BY choice ORDER BY percentage DESC;
+--------+------------+
| choice | percentage |
+--------+------------+
|      4 |    66.6667 |
|      1 |    16.6667 |
|      2 |    16.6667 |
+--------+------------+
3 rows in set (0.00 sec)

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

mysql>

   
    
    
    
    
    
    
  

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